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23:30
iCarto Blog: Sub-basin delimitation process using QGIS
sur Planet OSGeoThis article is part of our series on Delimitation of hydrographic sub-basins using QGIS and a DEM:
- Delimitation of hydrographic sub-basins using QGIS and a DEM
- Digital elevation models for hydrological studies
- Technical criteria for the delimitation of sub-basins
- Sub-basin delimitation process using QGIS (This post)
In this article we are going to explain the process to delimit the river sub-basins of a certain region using QGIS and a DEM. In this case the region is the entire Republic of Mozambique.
The starting data we need is a mosaic of Digital Elevation Models (DEMs) of the entire area and the watershed layer. As we commented in the previous articles of the series, we will use the NASADEM HGT mosaics (here we explain how to download them) and the basin layer elaborated by GEAMA.
Create single DEM (Mosaic)The first step is the union of the DEM mosaics to create a single DEM for all of Mozambique.
QGIS provides us with different options for joining raster files. In this case we are going to use the tool “Merge”. To do this, select “Raster” from the menu, display the “Miscellaneous” options and click “Merge”.
In the pop-up window we add all the input layers, that is, all the DEMs downloaded from the web of the area in which we are going to work. We give a path and a name for the output file, check the option “Open the output file after running the algorithm” and execute.
DEM reprojection
The merged DEM is in the WGS 84 Geographic Coordinate System (EPSG:4326). We reproject the DEM to a Projected Coordinate System. In our case to WGS 84 / UTM zone 37S (EPSG:32737). To reproject the DEM from the menu we select “Raster”, then “Projections” and “Warp (reproject)”.
In the input layer we select the combined DEM and indicate both the source CRS and the target CRS. We also indicate a path and a name for the output file and run the algorithm.
DEM clipping
To reduce the processing computation of the algorithms that we will use in the following steps, we will now clip the DEM per each river basin. Another reason for making these cuts is the difference in sizes and shapes of the basins that we are going to analyze. Better results will be obtained by analyzing each basin separately in order to adjust the parameters of the algorithms to each particular case instead of using the same parameters for all of Mozambique.
We create the masks for each basin from the basins layer. In the following image you can see the DEM in the background, in white the administrative limit of Mozambique and in blue the mask of the Lurio river basin.
Next, we clip the DEM with each created mask. To clip the DEM, in the main menu we select “Raster”, then “Extraction” and “Clip Raster by Mask Layer”.
In the pop-up window we select the reprojected DEM on the input layer and the basin mask on the mask layer. Also, so that the crop fits exactly to the edge of the basin and so that no black area is visible, we will specify a value for “no data”, for example -9999. Finally, we mark the following two options:
- Match the extent of the clipped raster to the extent of the mask layer.
- Keep resolution of input raster.
We specify the path and name for the output file and run the algorithm.
Perform this process for all basins. Batch processing can be used for this instead of doing it one by one.
Filling depressionsAlthough the latest versions of the DEMs are already processed with different corrections and gap filling, they may still contain artifacts such as depressions. Artifacts must be removed before using a DEM in hydrologic analysis. There are several algorithms for filling gaps (GDAL, GRASS, SAGA, …). The incorporation of the GRASS hydrological toolset in QGIS is very useful. We will therefore use the GRASS algorithm both for this step and for others that we will see later.
To fill depressions we wil use the processing toolboox, if it is not visible on the right side of the QGIS window, it can be enabled from the main menu, by select “Processing” and “Toolbox”.
In the toolbox find or type the following algorithm: r.fill.dir. In the dialog window select as input (Elevation) the clipped DEM and uncheck Flow direction and Problem areas. We are only interested in obtaining the DEM without depressions. Indicate the path and name for the output file and execute.
This geoprocess can take a long time to finish depending on the size of the raster and the power of the computer. Perform this geoprocess for all basins. Batch processing can be used for this instead of doing it one by one.
Drainage direction, accumulated flow, stream segments and sub-basinsNow that we have a corrected DEM, the next step is to calculate the drainage directions, accumulated flow, stream segments and sub-basins. To do this we look for the following algorithm in the toolbox: r.watershed
In the dialog window we select the corrected raster of the basin and establish the most appropriate “Minimum size of exterior watershed basin” for each case.
Because of the wide difference between the size of some basins and others, it is necessary to play with the “Minimum size of exterior watershed basin” to obtain the optimal results for each of them.
An average size can be obtained by reviewing the characteristics of the raster. The pixel size of the raster is 30x30m, so the “Minimum size of exterior watershed basin” must be at least 333,333.33 pixels, approximating 300,000 pixels.
But, in many cases, it is decided to establish 100,000 or less to solve some problems detected in some flat areas or mouths. Also check the following two options:
- Enable Single Flow Direction (D8) flow
- Allow only horizontal and vertical flow of water
Also check the boxes that can be seen in the following image, in addition to indicating the paths and names of the output files and execute the algorithm.
We thus obtain for each basin:
- Accumulated flow
- Drainage direction
- Sub-basins
- Stream segments
The only layer we are going to work on is the sub-basin layer, the rest are calculated to serve as support for small manual adjustments that we will make later.
Transform to vector layer
Once we have the sub-basins layer, the next step is to transform this raster layer into a vector layer. To do this we are going to look for the following geoprocess in the toolbox: r.to.vect. In the window, select the sub-basins layer as the input raster layer.
Also select these options and run:
- Feature type: area
- Smooth corners of area features
- v.out.ogr output type: area
Once we have the vector layer of sub-basins we have to review the result, join the necessary polygons to have only the sub-basins that meet the agreed criteria mentioned in the previous article and make small manual corrections where necessary.
The union of the polygons is also necessary because the algorithm creates sub-basins of tributaries that are not direct to the main river, that is, tributaries of a tributary of the main river. In this way we solve the problem.
These algorithms work well in sloping areas, but in flat areas they can give undesirable results, and it is necessary to review them. For example, in coastal areas with very flat basins, a more detailed review and adjustments to sub-basin boundaries were required based on other information such as drainage directions, rivers, etc.
Smoothing and simplification
When vectorizing a raster, the edges of the polygons are generated following the shape of the pixels, for this reason it is necessary to smooth them.
This leads to another problem, which is that smoothing creates many vertices that make the layer size increase quite a bit. To avoid this, after smoothing you can also do a simplification.
Choosing the appropriate parameters, smoothing and simplification are carried out without practically losing definition in the delimitation of the sub-basins. In the image below you can see the edges of the sub-basins before and after (red) smoothing and simplifying.
Sub-basins merge
Since we have created a sub-basin layer for each basin, we perform a vector layer union to create a single sub-basin layer for the entire country: mergevectorlayers.
In the dialog window we select all the sub-basin layers for input layers, we specify the Coordinate Reference System, the path and the name of the output file and we execute.
Geometric and topological checks and correctionsOnce we have the desired sub-basin layer, overlaps, duplicates, gaps, invalid geometries, etc. must be checked and corrected.
This can be done with plugins (Manage and install plugins)
Modify attribute table as needed
In addition to the geometry of the sub-basins, we must also add the desired attributes and order the attribute table as desired. Some examples of useful attributes in a sub-basin layer are the name of the river, the area, length of the main river or the basin to which it belongs.
Final ResultsFollowing these steps we obtain our layer of sub-basins.
With this article we close our series on the delimitation of sub-basins. Did you find them interesting? Do you use other techniques? Need help? Get in touch with us or write to us on Twitter.
La entrada Sub-basin delimitation process using QGIS se publicó primero en iCarto.
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10:01
The Energy Industry Map
sur Google Maps ManiaThe European Commission's interactive map The Energy and Industry Geography Lab provides an overview of Europe's energy infrastructure and the potential for developing cleaner energy.The inital map view of The Energy and Industry Geography Map shows the location of the various types of power plants and their individual capacity. This layer provides a wonderful overview of how individual -
19:00
The World's Crookedest Street
sur Google Maps ManiaDriving up Lombard Street Both Lombard Street, San Francisco and Snake Alley, Burlington, Iowa have at various times been announced as the bendiest, least straight roads in the world. It is debatable whether either road can truly claim to be the crookedest street in America, let alone the world. However we can perhaps settle the argument over whether Lombard Street is less straight than Snake
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15:26
GeoSolutions: Envitia is joining our partnership program
sur Planet OSGeoYou must be logged into the site to view this content.
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11:00
CARTO Blog: Using Spatial Analysis for 5G Rollout
sur Planet OSGeo5G has been the talk of the town (okay, world) for years. Afterall, from a bird’s eye view, who wouldn’t be excited to regularly experience faster downloads and less latenc...
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8:40
The Changing Face of Australia
sur Google Maps ManiaAustralian men don't do housework. The Australian 2021 census reveals that across Australia women are expected to do the washing, cooking, cleaning and laundry. The census found that in only one postcode area in the whole country (Oodnadatta) are men and women doing equal amounts of unpaid housework. Even in homes where women earn more than men women do more unpaid housework than the men. ABC -
10:03
Small Multiples of Global Heating
sur Google Maps ManiaGermany is heating up. Mean hot days per year in the districts In response to the recent extreme heat which has been experienced in much of the northern hemisphere a number of data visualization practitioners have turned to small multiple maps in order to show how climate change is leading to hotter temperatures over time. A small multiple is a series of maps (or graphs or charts) using the
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2:00
Ian Turton's Blog: Some interesting books I've read recently
sur Planet OSGeoInteresting BooksThis is a short post to let you know about some interesting books I’ve recently finished that you might find interesting.
The Atlas of Unusual BordersOr to give it its full title The Atlas of Unusual Borders: Discover intriguing boundaries, territories and geographical curiosities by Zoran Nikolic. I blame Barry Rowlingson who threw a link to it into a twitter discussion on borders, so I had to buy it. And, to be honest I’m very happy I did, it is an atlas of “interesting” border enclaves and other geographic oddities. So if like me you’ve ever wondered why Belgium has some many enclaves (and exclaves, and counter-enclaves) (or you just wondered what those are) this is the book that you need in your library. It also answers questions such as which capital city is a ghost town too? Plymouth, Montserrat to save you trying to look it up. This is a fascinating book with nearly every page leading to a “I didn’t know that”. My only minor quibble with it is the colour scheme of the maps, I really struggle with maps where the land is blue and the sea is grey, and with the highlights as yellow it is probably not a book for anyone with blue/yellow colour blindness.
git commit murder and git sync murderThis pair of books by Michael Warren Lucas, are murder mysteries set at technical conferences. If you have ever been to an open source conference (such as FOSS4G) then you will recognise many of the characters in these books. In the first book set at the (fictional) BSDNorth conference our hero Dale Whitehead sets out to give a technical talk but is sidetracked by the death of his room mate (and the weight of his laptop bag, which he seems to never get around to clearing out). I found this a very believable account of free software development, technical conferences and Unix hackers, though while I may have considered killing a user I’ve never actually done it!
git sync murder sees Dale forced to attend another conference despite his promise to himself to never leave his apartment ever again. Once again, things quickly spin out of his control and that laptop bag is no lighter than last time. I loved both these books and can thoroughly recommend them if you are at all into whodunits.
Finally, if you enjoy conferences/convention books then I’ll throw in Charlie Stross’ Dechlorinating the Moderator which I read in his collected Toast volume which reports from a futuristic 2018 Particulate 7: HiNRG & B-OND conference, for a fun short story.
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2:00
PostGIS Development: PostGIS 3.3.0beta1
sur Planet OSGeoThe PostGIS Team is pleased to release PostGIS 3.3.0beta1! Best Served with PostgreSQL 15 Beta2 and GEOS 3.11.0.
This release supports PostgreSQL 11-15.
3.3.0beta1
This release is a beta of a major release, it includes bug fixes since PostGIS 3.2.1 and new features.
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22:33
Sean Gillies: Korean-style sloppy joe
sur Planet OSGeoI had leftover ground beef and lamb from making burgers last night and turned that into no-recipe Korean-style sloppy joes for lunch on the deck with Ruth and Bea. I started by making a generous sofrito of onion, celery, yellow bell pepper, garlic, and ginger in a cast-iron skillet. When that had softened and started to color, I pushed it to one side and browned the meat (half a pound of beef, half a pound of lamb), stirring all of it together when the meat had cooked through and crisped a bit. For the sauce, I stirred in three tablespoons of vegetarian oyster sauce, a splash of black vinegar, a teaspoon of sesame oil, a quarter cup of gochujang, a teaspoon of salt, a tablespoon of sugar, half a teaspoon of black pepper, and half a cup of water. When it had reduced, I checked the salt, added a bit more, and then spooned it onto toasted buns. Sesame seeds, green onion (from my garden), and cucumbers dressed with rice wine vinegar provided the finishing touch.
Sloppy joe on a toasted brioche bun with quick pickles and watermelon
I like the traditional sloppy joe, too. But I like it even more with ginger and sesame oil. The mild, sweet funkiness of gochujang goes very well with lamb.
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8:24
Mapping Local Population Changes
sur Google Maps ManiaThe UK's Office of National Statistics has released a wonderful data visualization of the UK's latest population change statistics. Earlier this week the latest population and household estimates for England and Wales was released based on the 2021 census. You can discover how the population has changed near you on the ONS's How the Polpulation Changed Where Your Lived. One of the most -
12:46
The Climate Shift Index
sur Google Maps ManiaThe Climate Shift Index shows you how much global heating has influenced today's weather. Every day the Climate Shift Index map reveals where in the United States temperatures have been affected by climate change. The map reveals just how much global warming could be affecting the weather on any given day.The colors on the Climate Shift Index map where that day's temperatures are more or less
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11:34
GeoTools Team: GeoTools 26.5 released
sur Planet OSGeoThe GeoTools team is pleased to share the availability GeoTools 26.5 : geotools-26.5-bin.zip geotools-26.5-doc.zip geotools-26.5-userguide.zip geotools-26.5-project.zip This release is also available from the OSGeo Maven Repository and is made in conjunction with GeoServer 2.20.5Fixes and improvementsGrid aggregation in the ElasticSearch community module has been improvedFix aggregate queries -
11:00
CARTO Blog: Analyzing Sentiment & Footfall in Post-COVID Berlin
sur Planet OSGeoThe Data Appeal Company’s Hannah Babineau - International Partnerships and Marketing Manager - guest blogs for CARTO! -
2:00
GeoServer Team: GeoServer 2.20.5 Released
sur Planet OSGeoWe are happy to announce GeoServer 2.20.5 release is available with downloads (bin, war, windows), along with docs and extensions.
This is a maintenance release of the 2.20.x series recommended for production systems. This release was made in conjunction with GeoTools 26.5 and GeoWebCache 1.20.3.
Improvements and Fixes- The request logger is now configurable from the UI (form the “Global settings” panel),
- Importer improvements to support REPLACE mode on raster layers (in addition to the existing support for vector ones).
- The KML-PPIO module has graduated to extension (allows KML encoding of feature collections in WPS processes). It’s now included in the WPS plugin download.
- WPS fetching of remote inputs can be disabled.
- Allow controlling usage of headers in proxy base URL expansion at the workspace level.
For the full list of fixes and improvements, see 2.20.5 release notes.
About GeoServer 2.20Additional information on GeoServer 2.20 series:
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10:35
Mapping Vintage Newspapers
sur Google Maps ManiaThe Library of Congress' Chronicaling America project digitizes historic newspapers from across the United States. Using the site anyone can search and read historic newspaper stories published at any time from 1777-1963. A new interactive map now allows you to search these vintage newspapers by location. The new Exploring Chronicaling America Newspapers interactive map allows you to browse the
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12:41
Stefano Costa: An updated IOSA website
sur Planet OSGeoToday marks the 18th anniversary of IOSA, Internet and Open Source in Archaeology, the project/working group that I got started with Giovanni Luca Pesce in 2004. Luca Bianconi would join a few years later and give a substantial contribution to the development of the oldest active software project under the IOSA umbrella, Total Open Station.
It seems an appropriate time to announce that the iosa.it website is now available with a revamped look, and has become the single container for all content previously available in separate websites, such as the Quantitative Archaeology Wiki.
There will be no substantial improvements to the website, but I consider it a “living archive” so I’m going to add more content as I find it and have the time to organize it properly.
Please find it at [https:]] as usual, and browse like it’s 2004 again.
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11:00
CARTO Blog: Cost of Living Crisis: Location Intelligence for Energy Efficiency
sur Planet OSGeoRead any news website in 2022 and there’s one phrase you can’t escape; the “cost of living crisis.” In the UK, living costs have been rising at their fastest rate in 30 yea... -
10:17
iCarto Blog: Technical criteria for the delimitation of sub-basins
sur Planet OSGeoThis article is part of our series on Delimitation of hydrographic sub-basins using QGIS and a DEM:
- Delimitation of hydrographic sub-basins using QGIS and a DEM
- Digital elevation models for hydrological studies
- Technical criteria for the delimitation of sub-basins (This post)
- Sub-basin delimitation process using QGIS
To delimit the hydrographic sub-basins of a country, it is necessary to establish a series of criteria that allow uniform results to be obtained throughout the study area.
Basic criteriaIn this case, the following basic criteria were agreed with the Regional Water Administrations (ARAs):
- Sub-basins are not delimited in basins with an area of less than 3500 km2.
- Only the areas of the direct tributaries of the main river, which have a length equal to or greater than 55 km, are delimited as sub-basins.
- Only the areas of the direct tributaries of the main river that have an area equal to or greater than 300 km2are delimited as sub-basins.
In addition to the sub-basins resulting from the application of the basic criteria, the following areas were delimited for each river basin:
- Source area of the main river. In the case of transboundary rivers, that is, rivers that cross two or more states, the source may be outside the study area. In the case of Mozambique, there are several examples in which the source of the main river of the river basin is in another country (Zambezi, Limpopo, Incomati…). In these cases this area was not delimited.
- Area of the mouth of the main river.
- Area that includes the rest of the sub-basins, which do not meet the basic criteria, normally attached to the bed of the main river.
Exceptions
It was decided to delimit some sub-basins that did not meet the previous basic criteria and that we will call exceptions because they are sub-basins considered of great hydrological importance by the ARAs. An example of this is the delimitation of the sub-basins of the Umbelúzi River. Although the area of this basin is less than 3500 km2, it is of great hydrological importance because it contains a high percentage of large farms, with a very high demand for water.
In the next article, the last of the series, we will see how to do the whole process using QGIS.
La entrada Technical criteria for the delimitation of sub-basins se publicó primero en iCarto.
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9:42
Introducing Mapbox Globe View
sur Google Maps ManiaMapbox's 3D globe view is now available to all developers. The new globe map projection option in Mapbox GL and Mapbox mobile SDKs allows you to turn your 2D maps into fully interactive 3D globes. The new globe view includes a number of styling options which allow developers to "adjust the color of space, (the) visibility of stars, and the color of the atmosphere around a globe".If you want an -
19:00
Game of Populations
sur Google Maps ManiaThe UK's Office for National Statistics (ONS) has today released the latest population and household estimates for England and Wales based on the 2021 census. The population of England & Wales is now 59,597,300. In the previous census (2011) the population of England & Wales was 56,075,912 The UK population as a whole is now almost 67 million. In celebration of the new population data for
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18:10
GeoSolutions: OGC Disaster Pilot and GeoSolutions – Powering decision makers with the right information
sur Planet OSGeoYou must be logged into the site to view this content.
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9:51
They Paved Paradise
sur Google Maps ManiaUSA Parking Lots is an interactive map of the United States which blacks out every single parking lot in the country. Of course because this is America it means that if you zoom in on a major city the map displays a lot of black polygons.Because the map doesn't have a FAQ page I don't know how the data for the parking lots was obtained. If I was going to make a similar map for the UK I would -
18:30
Explore the Pyramids of Meroë
sur Google Maps ManiaFresh from climbing Mount Everest in 3D today I'm undertaking a tour of the Pyramids of Meroë. If you travel south down the River Nile through Egypt to Sudan, just before you get to Khartoum you will come to Meroë, the ancient capital of the Kushite Kingdom. Here you will discover an ancient city which is home to more than 200 pyramids. Google Arts and Culture's Pyramids of Meroë is a
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11:00
CARTO Blog: How Yale Climate Connections Uses Spatial Visualization for Community Engagement
sur Planet OSGeoWhat is the first thing that you do when you open a web map? For most of us, we scroll and scroll until we’re zoomed right in to exactly where we live to find out what’s ha...
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9:51
GoeGuessr for Art
sur Google Maps ManiaGeo Artwork is a fun game in which you have to guess where individual works of art were created. The game is very similar to the popular Geoguessr game, except instead of trying to work out the location of Google Maps Street View images you have to work out the origins of individual works of art.In Geo Artwork you are shown a painting (or another type of artwork) and using your knowledge of art
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5:56
Sean Gillies: Superior training week thirteen recap
sur Planet OSGeoWeek thirteen was my biggest week yet. I did a non-hilly speed workout on the dirt trails of Pineridge Natural Area, an uphill workout on Towers Trail, a tempo run at Maxwell, and two long runs on the weekend. I didn't feel great Friday, Saturday, or Sunday, but exceptionally nice running weather helped me survive the weekend miles.
12 hours, 15 minutes
57.0 miles
7,664 ft D+
I didn't take any photos during my runs this week. I'll try to do better this week.
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9:58
Where is Abortion Illegal?
sur Google Maps ManiaFollowing Friday's decision by the Supreme Court to overturn Roe vs Wade the legality of abortion has now been handed over to individual states. This means that a woman's right to choose in the United States depends on a patchwork of laws which range from states with outright bans on abortion to states where the right to choose is enshrined in law.To help inform women of their local laws
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15:40
QGIS Blog: QGIS 3.26 Buenos Aires is released!
sur Planet OSGeoWe are pleased to announce the release of QGIS 3.26 ‘Buenos Aires’!
Installers for all supported operating systems are already out. QGIS 3.26 comes with tons of new features, as you can see in our visual changelog. QGIS 3.26 Buenos Aires is named after last year’s FOSS4G host city.
We would like to thank the developers, documenters, testers and all the many folks out there who volunteer their time and effort (or fund people to do so). From the QGIS community we hope you enjoy this release! If you wish to donate time, money or otherwise get involved in making QGIS more awesome, please wander along to qgis.org and lend a hand!
QGIS is supported by donors and sustaining members. A current list of donors who have made financial contributions large and small to the project can be seen on our donors list. If you would like to become a sustaining member, please visit our page for sustaining members for details. Your support helps us fund our six monthly developer meetings, maintain project infrastructure and fund bug fixing efforts.
QGIS is Free software and you are under no obligation to pay anything to use it – in fact we want to encourage people far and wide to use it regardless of what your financial or social status is – we believe empowering people with spatial decision making tools will result in a better society for all of humanity.
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9:48
Climb Mount Everest in 3D
sur Google Maps ManiaMount Everest 3D is an impressive 3D map of the world's tallest mountain and the peaks which surround it in the Himalyayas. The map uses high resolution aerial imagery draped over a 3D digital elevation model to provide a unique view of one of the world's most beautiful and inspiring landscapes.As wall as being able to pan around and zoom in on the wonders of the Mahalangur Himal sub-range of
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22:56
longwayaround.org.uk: Web Mercator OS Vector Tile API in OpenLayers
sur Planet OSGeoAdding a Vector Tile layer of Ordnance Survey data from the OS Data Hub to an OpenLayers map in Web Mercator is a little more work than expected as the JSON style document and associated JSON source document include paths for the default British National Grid tiles. The following is …
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18:18
A Brief History of Time & Space
sur Google Maps Maniathe shifting borders of the Holy Roman Empire from 1000-1750 Point in History is an interactive map which allows you to explore country and regional borders over time. The map uses historical boundaries data from the Historical Boundaries Project in order to show how the boundaries of countries around the world have developed and changed through history.If you click anywhere on the map a
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11:00
CARTO Blog: CARTO and Google Cloud Announce Climate Insights for Infrastructure
sur Planet OSGeoThe ever-growing threat of climate change on the built environment cannot be ignored. Intensifying wildfires, storms, floods and sea level rise not only impact the health a...
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10:28
The Drunken Spider Crawl
sur Google Maps ManiaToday I finally got around to creating my own 'data spider' map, inspired by William Davis's viral Hub and Spoke interactive map. My Drunken Spider Map can help you find the ten nearest bars to any location in London or New York. If you pan around the map then the 'spider' will walk around the map, so that it is always pointing to the ten nearest bars to the center of the map.Cloning William's
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10:00
Paul Ramsey: Technology, Magic & PostgreSQL
sur Planet OSGeoI have a blog post up today at Crunchy Data on some of the mechanisms that underlie the PostgreSQL query planner, it’s pretty good if I do say so myself.
I was motivated to write it by a conversation over coffee with my colleague Martin Davis. We were talking about a customer with an odd query plan case and I was explaining how the spatial statistics system worked and he said “you should do that up as a blog post”. And, yeah, I should.
One of the things that is striking as you follow the PostgreSQL development community is the extent to which a fairly mature piece of technology like PostgreSQL is stacks of optimizations on top of optimizations on top of optimizations. Building and executing query plans involves so many different paths of execution, that there’s always a new, niche use case to address and improve.
I worked a political campaign a few years ago as a “data science” staffer, and our main problem was stitching together data from multiple systems to get a holistic view of our data.
That meant doing cross-system joins.
The first cut is always easy: pull a few records out of System A with a filter condition and then go to System B and pull the associated records. But then inevitably a new filter condition shows up and applied to A it generates so many records that the association step on B gets overloaded. But it turns out if I start from B and then associate in A it’s fast again.
And thus suddenly I found myself writing a query planner and executor.
It’s only when dumped into the soup of having to solve these problems yourself that you really appreciate the magic that is a mature relational database system. The idea that PostgreSQL can take a query that involves multiple tables of different sizes, with different join cardinalities, and different indexes and figure out an optimal plan in a few milliseconds, and then execute that plan in a streaming, memory efficient way…?
Magic is really the best word I’ve found.
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22:56
longwayaround.org.uk: Writing small text filters for the shell and Vim
sur Planet OSGeoText filters are command-line programs that take text as input, transform it then output the results. An example of a common built in text filter is sort which when passed newline separated text will sort each line:
printf 'b\nc\na' | sort
You can write your own text filter scripts …
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10:47
Brooklyn Bridge is Falling Down
sur Google Maps ManiaBrooklyn Bridge may not be about to fall down any time soon, however according to the U.S. National Bridge Inventory Map it is in 'poor condition'. Esri's U.S. National Bridge Inventory Map uses government data to map the age and condition of bridges over 100 years old in the United States. The map can be used to discover the condition of bridges across the country and view data on how much
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10:16
iCarto Blog: Digital elevation models for hydrological studies
sur Planet OSGeoThis article is part of our series on Delimitation of hydrographic sub-basins using QGIS and a DEM:
- Delimitation of hydrographic sub-basins using QGIS and a DEM
- Digital elevation models for hydrological studies (This post)
- Technical criteria for the delimitation of sub-basins
- Sub-basin delimitation process using QGIS
A digital elevation model (DEM) is a visual and mathematical representation that describes the altimetry of an area through a set of terrain elevations. The vegetation and infrastructures created by man (buildings, bridges, power lines, etc.) are not included, it only represents the relief of the ground.
DEMs are particularly useful in hydrological modeling (delimitation of basins, calculations of flow accumulations, flow directions), soil mapping and territorial planning.
There are currently quite a few sources that allow you to download DEMs with worldwide coverage for specific areas for free and without restrictions on use. The availability, updating and improvement of quality and precision of the DEMs represent a great contribution to the studies.
We do not analyze in this article other options subject to the payment of a license for their download and/or use.
Global DEMSome of the most widely used global DEMs for hydrological analysis worldwide and freely available are the following:
- SRTMGL1 v003 (1 arc-second, 30 meters) and SRTMGL3 v003 (3 arc-secondar, 90 meters): The Shuttle Radar Topography Mission (SRTM) data sets are the result of collaboration between NASA and the National Geospatial-Intelligence Agency (NGA), with the participation of the German and Italian space agencies. The purpose of SRTM was to generate a digital elevation model. These MDEs are the best known and used globally. Version 3 is derived from the SRTM v2 data, but removes the gaps that were present in previous versions of the SRTM data. The gaps are filled by ASTER Global Digital Elevation Model (GDEM) Version 2.0, Global Multi-solution Terrain Elevation Data 2010 (GMTED2010), and National Elevation Dataset (NED). It offers resolutions of 1 and 3 seconds of arc, or what is the same resolutions between 30 and 90 meters.
- NASADEM HGT v001: (1 arc-second, 30 meters): The resolution of NASADEM is found in 1 degree of arc (just over 110 pixel kilometers) along the earth’s surface between 60º North and 56º South latitude, or what is the same as 30 meters of spatial resolution. This DEM is derived from SRTM data, fine-tuned with ASTER GDEM v2 data, incorporating GLAS ground control points, and developing additional backscatter and radiometric correction layers. Other enhancements include the use of GDEM and PRISM AW3D30 DEM, and gap fill interpolation.
- ASTER GDEM V3: ASTER GDEM Version 3 data products (1 arc-second, 30 meters) offer substantial improvements in coverage and reduction in the appearance of artifacts. It also provides improved spatial resolution and higher horizontal and vertical accuracy. Version 3 shows significant improvements over the previous version. However, it is cautioned that the data still contains anomalies and artifacts that will reduce its effectiveness for use in certain applications.
- ALOS PALSAR: This DEM is one of the resources available within the Japan Aerospace Exploration Agency (JAXA) ALOS satellite products. ALOS (Advanced Land Observation Satellite) also known as DAICHI, carries three sensors on board: the PRISM for panchromatic images, the PALSAR synthetic aperture radar and the AVNIR radiometer. It has higher spatial resolution than the SRTM and ASTER models, native resolution of 30 and 12.5 meters resampled.
It does not exist a perfect model in order to delimitate all kind of river basins, but we need to select the onee that best suits our use case.
To carry out the delimitation of the sub-basins of Mozambique, the iCarto team decided to use NASADEM. The decision to select this model over others was based on several criteria:
- The starting layer of basins was made at the time from STRM data. The sub-basin layer had to be adjusted to this layer, so it was more appropriate to use a DEM also obtained from the Shuttle Radar Topographic Mission data.
- NASADEM is the most updated and corrected DEM of the models that come from STRM data.
- After reviewing different studies, it was concluded that for the delimitation of these sub-basins there would be no significant differences in the results obtained with any of the products with a resolution of 30 meters. Several studies have been published evaluating the vertical accuracy of these products. One of them is that of González-Morada and Viveen, who compared the ASTER GDEM, SRTM, AW3D30 and TanDEM-X DEMs with a set of 139 measurements collected by a dual-frequency Trimble 5800 GNSS receiver. The root mean square error (RMSE) was below 7 meters for all models.
- Some tests were carried out using various models and it was concluded that a resolution of 30 m was sufficient for this study. A higher resolution would imply excessively high processing times in exchange for an insignificant increase in precision for this analysis.
NASADEM products can be downloaded from different platforms, two of the best known are:
- EARTHDATASEARCH (NASA’s browser)
- EARTHEXPLORER (USGS’s browser)
In both cases, the download is free, only prior registration is required.
To download the NASADEM, for example, from the EarthExplorer search engine, it is only necessary to indicate the study area in the “Search Criteria” tab, search for and select “NASADEM_HGT” in the “Data Sets” tab, go to results and download all the files.
In the following articles of this series we will work on the DEM with QGIS and we will define the criteria for the delimitation of the sub-basins.
La entrada Digital elevation models for hydrological studies se publicó primero en iCarto.
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0:34
Martin Davis: JTS 1.19 Released
sur Planet OSGeoJTS 1.19 has just been released! There is a great deal of new, improved and fixed functionality in this release - see the GitHub release page or the Version History for full details.
This blog has several posts describing new functionality in JTS 1.19:
New Functionality- Concave Hull of Polygons
- Algorithm for Concave Hull of Polygons
- Outer and Inner Concave Polygon Hulls
- Using Outer Hulls for Smoothing Vectorized Polygons
- Concave Hulls
- Polygon Triangulation
- Cubic Bezier Curves
- Offset Curves
Many of these improvements have been ported to GEOS, and will appear in the soon-to-appear version 3.11. In turn this has provided the basis for new and enhanced functions in the next PostGIS release, and will likely be available in other platforms via the many GEOS bindings and applications. -
11:00
CARTO Blog: Spatial Data Monetization: A Quick Guide
sur Planet OSGeoData monetization is a concept that we hear about more every day thanks to the increasing availability and variety of new business intelligence and data science platforms, ... -
10:00
Paul Ramsey: Some More PostGIS Users
sur Planet OSGeoThe question of why organizations are shy about their use of open source is an interesting one, and not completely obvious.
Open source luminary Even Roualt asks:
is there some explanation why most institutions can’t communicate about their PostGIS use ? just because it is a major hurdle for technical people to get their public relationship department approve a communication ? people afraid about being billed about unpaid license fees ? ?
There’s really very little upside to publicizing open source use. There’s no open source marketing department to trumpet the brilliance of your decision, or invite you to a conference to give you an award. On the other hand, if you have made the mistake of choosing an open source solution over a well-known proprietary alternative, there is surely a local sales rep who will call your boss to tell them that you have made a big mistake. (You do have a good relationship with your boss, I hope.)
These reverse incentives can get pretty strong. Evendiagram reports:
Our small group inside a large agency uses postgis. We don’t talk about it, even internally, to avoid the C-suite forcing everyone back to oracle. RHEL repos allow us a lot of software that would otherwise be denied.
This reminds me of my years consulting for the British Columbia government, when technical staff would run data processing or even full-on public web sites from PostgreSQL/PostGIS machines under their desktops.
They would tell their management it was “just a test system” or “a caching layer”, really anything other than “it’s a database”, because if they uttered the magic word “database”, the system would be slated for migration into the blessed realm of enterprise Oracle systems, never to be heard from again.
LogosMeanwhile, Daryl Herzmann reminds us that the Iowa Mesonet has been on Team PostGIS since 2003.
Iowa Environmental Mesonet, Iowa State University
- Data being managed in the database
Meteorological Data, “Common” GIS datasets (roads, counties), Current and Archived NWS Tornado/Flash Flood/Thunderstorm Warnings, Historical Storm Reports, Current and Archived precipitation reports. Climate data - How the data is being accessed / manipulated
From mapserver! Manipulated via Python and PHP. - Why you chose to use PostGIS for the application
Open-Source. Uses my favorite DB, Postgres. Easy integration with mapserver. The support community is fantastic!
Further afield, the GIS portals of governments throughout Ukraine are running on software built on PostGIS.
Jørgen Larsen de Martino notes that:
The Danish Agency for Data Supply and Infrastructure uses PostGIS extensively - and have been using it for the last 10 years - we would not have had the success we have was it not for @PostGIS.
CounterpointThe Utah Geospatial Resource Center uses PostGIS to provide access to multiple spatial layers for direct access in a cloud-hosted PostGIS database called the “Open SGID”. (I can hear DBA heads exploding around the world.)
While self-reporting is nice, sometimes just a little bit of dedicated searching will do. Interested in PostGIS use in the military? Run a search for “postgis site:mil” and see what pops up!
The 108th wing of the Air Force! Staff Sgt. Steve De Leon is hard at it!
“I’m taking all the data sources that AMC and A2 compile and indexing them into the PostgreSQL/PostGIS data and then from there trying to script Python code so the website can recognize all the indexed data in the PostgreSQL/PostGIS database,” said the De Leon.
The Canadian Department of National Defense is building Maritime Situational Awareness Research Infrastructure with a PostgreSQL/PostGIS standard database component.
PostgreSQL with its PostGIS extension is the selected DBMS for MSARI. To ease mainte- nance and access, if more than one database are used, PostgreSQL will be selected for all databases.
The Coast Guards “Environmental Response Management Application (ERMA)” is also running PostGIS.
The application is based on open source software (PostgreSQL/PostGIS, MapServer, and OpenLayers), that meet Open Geospatial Consortium (OGC) specifications and standards used across federal and international geospatial standards communities. This ensures ERMA is compatible with other commercial and open-source GIS applications that can readily incorporate data from online data projects and avoids licensing costs. Open-source compatibility supports data sharing, leverages existing data projects, reduces ERMA’s maintenance costs, and ensures system flexibility as the technology advances. Because ERMA is open source, it can easily be customized to meet specific user requirements.
Want to appear in this space? Email me!
- Data being managed in the database
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9:56
100 Years of Climate Data
sur Google Maps ManiaThe European Climate Assessment & Dataset project records data for more than 15,000 weather stations across Europe. This data includes historical temperature and precipitation records dating back as far as the 19th Century. The data provides comprehensive evidence of how climate change has contributed to extreme rises in temperature across the whole of Europe. The Climate ECAD Map uses this
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1:16
Sean Gillies: Superior training week twelve recap
sur Planet OSGeoIn my training program the last week of every four week block is dedicated to rest and recovery. I did much less running in week twelve, more bike riding, and some yoga. I did more household stuff, re-watched Stranger Things season three and started season four with my family, and got some excellent nights of sleep. Here are the running numbers.
3 hours, 12 minutes
15.0 miles
2,231 ft D+
My Saturday run at Lory State Park unexpectedly coincided with the XTERRA Lory Triathlon but I did manage to find a parking spot at Arthur's Rock trailhead and do a loop that only barely intersected the mountain bike portion of the event. A lot of local runners were in Wyoming for the Bighorn Trail Run, so I had the remote parts of the park all to myself.
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10:00
Paul Ramsey: Some PostGIS Users
sur Planet OSGeoLast week, I wrote that getting large organizations to cop to using PostGIS was a hard lift, despite that fact that, anecdotally, I know that there is massive use of PostGIS in every sector, at every scale of institution.
Simple CluesHere’s a huge tell that PostGIS is highly in demand: despite the fact that PostGIS is a relatively complex extension to build (it has numerous dependencies) and deploy (the upgrade path between versions can be complex) every single cloud offering of PostgreSQL includes PostGIS.
AWS, Google Cloud, Azure, Crunchy Bridge, Heroku, etc, etc. Also forked not-quite-Postgres things like Aurora and AlloyDB. Also not-Postgres-but-trying things like Cockroach and Yugabyte.
If PostGIS was a niche hobbyist project…? Complete the sentence any way you like.
LogosTrue to form, I received a number of private messages from people working in or with major institutions you have heard of, confirming their PostGIS use, and the fact that the institution would not publicly validate it.
However, I also heard from a couple medium sized companies, which seem to be the only institutions willing to talk about how useful they find open source in growing their businesses.
Hailey Eckstrand of Foundry Spatial writes to say:
Foundry Spatial uses PostGIS in development and production. In development we use it as our GIS processing engine and warehouse. We integrate spatial data (often including rasters that have been loaded into PostGIS) into a watershed fabric and process summaries for millions of watersheds across North America. We often use it in production with open source web tooling to return results through an API based on user input. One of our more complex usages is to return raster results within polygons and along networks within a user supplied distance from a click location. We find the ease and power of summarizing and analyzing many spatial datasets with a single SQL query to be flexible, performant, efficient, and… FUN!
Dian Fay of Understory writes in:
We use PostGIS at Understory to track and record storms, manage fleets of weather stations, and optimize geographic risk concentration for insurance. PostGIS lets us do all this with the database tools we already know & love, and without severing the connections between geographic and other categories of information.
Want to appear in this space? Email me!
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9:53
Mapping the French Election
sur Google Maps ManiaMacron's En Marche! party has failed to win a majority in France's new National Assembly following strong performances by the left-wing alliance and the far right. The president's En Marche! won the most seats of any party in the national election. However the 245 seats won by Macron fall well short of the 289 seats needed for an overall majority in the National Assembly and far short of the
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14:04
Free and Open Source GIS Ramblings: MovingPandas v0.10 released!
sur Planet OSGeoThe latest v0.10 release is now available from conda-forge.
This release contains some really cool new algorithms:
- First initial MovingFeatures JSON (MF-JSON) support
- Improved handling of local non-geographic coordinates, incl a new tutorial on this topic
- Speed and direction column names can now be customized
If you have questions about using MovingPandas or just want to discuss new ideas, you’re welcome to join our recently opened discussion forum.
As always, all tutorials are available from the movingpandas-examples repository and on MyBinder:
Besides others examples, the movingpandas-examples repo contains the following tech demo: an interactive app built with Panel that demonstrates different MovingPandas stop detection parameters
To start the app, open the stopdetection-app.ipynb notebook and press the green Panel button in the Jupyter Lab toolbar:
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15:23
Stefano Costa: San Terenziano
sur Planet OSGeoA Marzano si festeggia San Terenziano (San Ransiàn) il 1° settembre o la prima domenica di settembre, anche se la chiesa di Marzano è dedicata a San Bartolomeo (che si festeggia una settimana prima, il 24 agosto).
Premesso che è comunque una generica “festa di fine estate”, è interessante notare che entrambi i santi sono protomartiri.
C’è una ricorrenza di associazioni tra San Terenziano e San Bartolomeo, anche se in località vicine: Rezzoaglio (GE) dove San Bartolomeo è festeggiato a Magnasco, Leivi (GE), Cavriago (RE). Tuttavia il culto di San Bartolomeo è molto diffuso in tutta Italia, mentre quello di San Terenziano è più raro.
Il sito www.encyclocapranica.it non è più online ma anni fa vi ho trovato questa interessante lista tratta da una pubblicazione a stampa (purtroppo non sembra archiviata nemmeno sulla Wayback Machine). La tematica è ripresa sul sito Capranica Storica sempre a cura di Massimo Brizzolara. Unica correzione apportata riguarda la località Rosso, che si trova in comune di Davagna e non di Lavagna.
- Recco (Comune di Recco, Arcidiocesi di Genova): si ricorda una cappella intitolata al Santo, mutata in San Rocco tra il sec. XV e il sec. XVI dopo una grave pestilenza (concomitante culto di San Rocco);
- Premanico (già appartenente al Comune di Apparizione, ora Comune di Genova, Arcidiocesi di Genova): esistono ruderi di chiesetta intitolata al Santo (concomitante culto di San Rocco);
- Pino (Comune di Genova, Arcidiocesi di Genova): chiesa parrocchiale intitolata a San Michele e Terenziano, patrono del luogo. Si ricorda il cosiddetto olio di San Terenziano, benedetto e distribuito alla popolazione in occasione della festa, che possiede virtù taumaturgiche per la cura dei reumatismi e delle artriti. Vi esiste anche una confraternita dal titolo dei Santi Michele e Terenziano;
- Rosso (Comune di Davagna, Arcidiocesi di Genova): località intitolata al Santo;
- Teriasca (Comune di Sori, Arcidiocesi di Genova): la locale chiesa di San Lorenza, fu originariamente edificata sotto il titolo dei Santi Lorenzo e Terenziano (concomitante culto di San Rocco);
- Fumeri (Comune di Mignanego, Arcidiocesi di Genova);
- Rezzoaglio (Diocesi di Bobbio-Piacenza): patrono del luogo (concomitante culto di San Rocco);
- Leivi (Diocesi di Chiavari): con cappella intitolata ai santi Terenziano e Desiderio;
- San Terenziano (Comune di Leivi): patrono del luogo;
- Nicorvo (Diocesi di Vigevano): patrono del luogo, con chiesa parrocchiale propria e chiesa rurale;
- Rompeggio (Comune di Ferriera Diocesi di Piacenza-Bobbio): patrono del luogo;
- Ebbio (Comune di Bettola Diocesi di Piacenza-Bobbio): patrono del luogo, con chiesa parrocchiale propria;
- Groppo Ducale (Comune di Bettola Diocesi di Piacenza-Bobbio);
- Isola di Compiano (Comune di Compiano Diocesi di Parma): patrono del luogo, vi si svolge una “Fiera Millenaria di San Terenziano” in occasione della festa;
- Gorro (Comune di Borgotaro Diocesi di Parma): patrono del luogo;
- Fraore (Comune di Parma Diocesi di Parma): patrono del luogo, con chiesa parrocchiale propria;
- Soragna (Diocesi di Parma): si ricorda una fiera in onore del Santo all’interno della Rocca;
- San Terenziano (Comune di Cavriago Diocesi di Reggio Emilia): con chiesa parrocchiale propria;
- Raiano di Cornio (Diocesi di Sulmona-Valva): con eremo dell’XI sec. intitolato al Santo;
- Capua (Arcidiocesi di Capua): si ricorda una chiesa intitolata al Santo, già nel XIII sec., fatta demolire da Federico II di Svevia per far posto all’edificazione della porta della Città;
- Tortona (Diocesi di Tortona): vi si ricorda un vescovo Terenziano, martirizzato nel 186 d.C., ma non è certo che sia lo stesso Terenziano di Todi;
- San Terenziano (Comune di Gualdo Cattaneo Diocesi di Todi): con chiesa parrocchiale e tomba del Santo;
- Teano (Diocesi di Teano): con reliquie (un braccio) ed officiatura approvata;
- Capranica (Diocesi di Civitacastellana): patrono del luogo, con reliquie (il cranio e un braccio), officiatura approvata e chiesa propria. Vi esiste una confraternita intitolata ai Santi Terenziano e Rocco;
- Todi (Diocesi di Todi): officiatura con lezioni proprie e rito doppio di II classe, festa celebrata nella Città e in tutto il territorio diocesano il 1° settembre di ogni anno.
Ho letto per la prima volta una sintesi con ipotesi storiche su questa diffusione riguardo a Rezzoaglio, un documento di qualche anno fa ma sempre molto interessante.
C’è una concentrazione del culto nell’Italia centrale e soprattutto nell’Appennino Ligure-Emiliano e Genovesato. Dall’elenco dei 25 luoghi, a cui si aggiunge Marzano, ho creato una mappa digitale. Certamente chi ha prodotto questo filmato ha usato lo stesso elenco. Altri riferimenti ma privi di elenchi sono sul sito santiebeati.it. Un elenco abbastanza completo è su CathoPedia. Tutti questi elenchi sono comunque incompleti, ma hanno il pregio di registrare notizie altrimenti difficili da reperire, un po’ come quella che associa San Terenziano a Marzano.
Mappa della diffusione del culto di San Terenziano in Italia
Dal punto di vista geografico, Marzano ricade pienamente nella zona di attestazione, anzi è quasi un punto di collegamento tra le presenze del versante ligure e quelle del versante padano.
Mappa della diffusione del culto di San Terenziano in Liguria e nell’Appennino settentrionale
Come abbiamo già avuto modo di vedere le notizie storiche su Marzano sono piuttosto scarne, ma a San Terenziano doveva essere già essere dedicata la prima cappella precedente alla chiesa.
Pillole di storia marzanina
La chiesa di San Bartolomeo · San Terenziano
Marzano 200 anni fa · La peste a Marzano nel 1656-1657
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10:23
Backup Ukraine
sur Google Maps ManiaAccording to Ukraine's Ministry of Culture Russia has already destroyed over 300 buildings and sites of cultural importance in Ukraine. This includes the total destruction of 9 cultural heritage sites in the Donetsk, Kyiv, Sumy and Chernihiv regions. In response to this destruction of Ukraine's cultural and historical heritage the Backup Ukraine project is helping volunteers to capture and -
10:54
Cool Off with a Climate Stripe Fan!
sur Google Maps ManiaHas Global Warming got you sweating this summer? Don't worry. And don't get all hot under the collar about climate change. Instead just sit back & relax and cool yourself off with a strikingly beautiful Climate Stripe Fan.The Berliner Morgenpost's Climate Stripe Fan is the perfect answer to this summer's record breaking heat waves. Let's face it world leaders and global corporations will do
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0:22
Sean Gillies: Superior training weeks ten and eleven recap
sur Planet OSGeoOnce again I've fallen behind on blogging about running, but will catch up. Week ten started out pretty well, but hay fever and lethargy were dragging me down at the end. I struggled on steep trails at Greyrock Saturday and then opted for more mellow long miles on Sunday. I've blogged about the route to Greyrock before, it's amazing.
9 hours, 33 minutes
44.0 miles
6,932 ft D+
View south over the Greyrock meadows on a hot Saturday.
I felt much better in week eleven. I did some hard hill intervals on Wednesday and back-to-back long runs with plenty of climbing on the weekend.
11 hours, 45 minutes
50.0 miles
9,633 ft D+
Saturday I ran in toasty warm conditions at Lory and Horsetooth. Even though I cut it short, this run had the most elevation gain of my season. After I got home and saw that more hot weather was in store for Sunday, I decided to head to the high country on Sunday. I succeeded in getting a timed entry reservation for Rocky Mountain National Park (RMNP), an hour away by car, and did a long loop from the Cub Lake trailhead.
Cub Lake trailhead in RMNP.
Sunday's run didn't have as much D+ as Saturday's, but it did start above 8,000 ft and went for more than 3 miles above 10,000 ft. I was traveling exclusively on snow for about two hours. Very comfortable, but very slow, and in one spot a bit sketchy. On the descent to Odessa Lake, the well-engineered trail crosses a steep gully, no problem in summer, but in spring the gully and trail are completely covered with snow and a slip on this traverse could result in a long downhill ride. It was exciting! The party ahead of me on the trail almost turned back.
Approaching the pass between Bear Lake and Odessa Lake.
In the last mile of the run I saw a big ole male moose just a few yards off the trail. This is normal for an outing in Moraine Park. On the drive home I saw a chonky black bear on the right bank of the Big Thompson River. I would have pulled over to get a photo to share here except the shoulder was completely filled with cars and my phone was dead.
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18:19
Free and Open Source GIS Ramblings: Building an interactive app with geocoding in Jupyter Lab
sur Planet OSGeoThis post aims to show you how to create quick interactive apps for prototyping and data exploration using Panel.
Specifically, the following example demos how to add geocoding functionality based on Geopy and Nominatim. As such, this example brings together tools we’ve previously touched on in Super-quick interactive data & parameter exploration and Geocoding with Geopy.
Here’s a quick preview of the resulting app in action:
To create this app, I defined a single function called
my_plot
which takes the address and desired buffer size as input parameters. Using Panel’sinteract
andservable
methods, I’m then turning this function into the interactive app you’ve seen above:import panel as pn from geopy.geocoders import Nominatim from utils.converting import location_to_gdf from utils.plotting import hvplot_with_buffer locator = Nominatim(user_agent="OGD.AT-Lab") def my_plot(user_input="Giefinggasse 2, 1210 Wien", buffer_meters=1000): location = locator.geocode(user_input) geocoded_gdf = location_to_gdf(location, user_input) map_plot = hvplot_with_buffer(geocoded_gdf, buffer_meters, title=f'Geocoded address with {buffer_meters}m buffer') return map_plot.opts(active_tools=['wheel_zoom']) kw = dict(user_input="Giefinggasse 2, 1210 Wien", buffer_meters=(0,10000)) pn.template.FastListTemplate( site="Panel", title="Geocoding Demo", main=[pn.interact(my_plot, **kw)] ).servable();
You can find the full notebook in the OGD.AT Lab repository or run this notebook directly on MyBinder:
To open the Panel preview, press the green Panel button in the Jupyter Lab toolbar:
I really enjoy building spatial data exploration apps this way, because I can start off with a Jupyter notebook and – once I’m happy with the functionality – turn it into a pretty app that provides a user-friendly exterior and hides the underlying complexity that might scare away stakeholders.
Give it a try and share your own adventures. I’d love to see what you come up with.
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16:15
QGIS Blog: QGIS Userbase Analytics
sur Planet OSGeoBackgroundUnderstanding which regions QGIS is being used in, which versions are in active use, which platforms it is being used on, and how many users we have is hugely beneficial to our ability as a project to serve our users. Back in 2017 at the bi-annual QGIS hackfest in Nødebo, Denmark, we had a long discussion about key project goals and the need to better understand our user base in order to plan the future direction of the project, and allocate funding and resources to where they are needed most
Typically proprietary software vendors have ready access to detailed user data through telemetry code which they embed in their software. This telemetry code ‘phones home’ key metrics, which together with other techniques such as license sales analysis gives them a very detailed insight into their user base. The data these vendors collect is typically not shared, so their users do not benefit from being able to understand how their data is used.
For QGIS.org, having to resort to what are generally considered to be nefarious and privacy-invading techniques of siphoning user data from our users goes against the ethos we try to promote as an open project. Further, since QGIS is freely available and doesn’t require any self-registration, we do not have a user database we can consult for such analytics. Additional factors make understanding usage levels hard. For example, a single user can download a copy of a QGIS installer and distribute it to many other users, and conversely web crawlers and bots can download many copies of QGIS installers and never install them. Because of this, simply counting the number of downloads from our website does not give a useful picture of our user base.
So we needed to come up with an approach that:
- Does not invade our user’s privacy
- Does not require including telemetry code in QGIS which exfiltrates user information from their system
- Does not store any user-identifiable data on our servers
- Is open and transparent in the data collection methodology
- Openly shares the insights we gain from our analytics to the broader community
The most obvious privacy-respecting way we could find to understand more about our users was to collect metrics of access to the QGIS News Feed. In order to display the latest news on startup, QGIS Desktop makes a request to [https:]] when it is opened. On the server that hosts the feed, we can then use the web server logs to understand which operating system and version of QGIS made the news feed request. Additionally, using the GeoIP library we can resolve each request to the country from which it originated. These pieces of information are included in the User-Agent headers sent by QGIS when it makes a request to the QGIS News Feed.
This process is anonymous, transparent, and simple to disable. It does not identify unique machines. Only one event is logged per unique network per hour. Only one event is logged per QGIS installation per day, and the event is only triggered when the user opens the QGIS Desktop application.
Operating system statistics are derived from QGIS version information, and no system fingerprinting or telemetry is implemented.
Location information is derived from the request source IP address, which is immediately discarded on the server after resolving it to the country of origin.
No logging on the QGIS News Feed server occurs with legacy installations that do not have the news feed feature, offline usage of QGIS, and installations for which feed collection is disabled (see below for info on how to disable it). It will also have statistics skewed in scenarios where atypical networking infrastructure is in effect, such as using a virtual private network.
Despite these caveats, the statistics should provide a good high-level overview of how QGIS is being used, such as the breakdown of QGIS across operating systems and versions – information that is incredibly useful to the QGIS developer team. Only the following four pieces of information are collected:
- The date (aggregated by day)
- The QGIS version
- The Operating System
- Country (based on IP which is immediately discarded)
If you wish to opt-out of this data collection, simply disabling the feed retrieval, using QGIS offline, or blocking access to the QGIS RSS feed address (feed.qgis.org) on your network will exclude you from this process. QGIS Desktop provides options for disabling version checking and feed access under
Settings ? Options ? General ? Application
. Note that by default this setting is specific to each individual user profile.Viewing the analytics
We have made a public dashboard publicly available at [https:]] . The dashboard was made using the fantastic open-source Metabase analytics package.
Credits: This post was written by Charles Dixon-Paver and Tim Sutton
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11:00
3liz: Lizmap sur le Socle interministériel de logiciels libres
sur Planet OSGeoLizmap sur le Socle Interministériel de Logiciels LibresLizmap est maintenant référencé sur le Socle interministériel de logiciels libres (SILL). Vous pouvez consulter la fiche du logiciel Lizmap. Elle a été créée par un référent SILL : un agent public utilisant Lizmap.
Pour qu'elle puisse être créée, une autre fiche Lizmap sur le Comptoir du libre et également une fiche Lizmap sur Wikidata ont été créées.
Le Socle interministériel de Logiciels LibresLe Socle interministériel de logiciels libres (SILL) est le catalogue de référence des logiciels libres recommandés par l'État pour toute l'administration.
Il est publié par le pôle logiciels libres d'Etalab (DINUM) sur le site code.gouv.fr. Son interface de gestion est accessible sur le site sill.etalab.gouv.fr.
Il est construit de façon collaborative par une communauté d'agents publics, les référents SILL. En tant qu'agents publics utilisateur de Lizmap, vous pouvez devenir référents Lizmap.
Pour en savoir plus sur le SILL, vous pouvez vous rendre sur cette définition par SourceHut.
Vous trouverez aussi les fiches de :
Le comptoir du libreLe Comptoir du Libre recense les logiciels libres métiers utiles aux services publics ainsi que leurs utilisateurs et prestataires.
Il s'agit d'une place de marché du logiciel libre métier. Elle a vocation à partager les informations relatives à ces logiciels, et à mettre en contact les parties intéressées. Les collectivités naviguant sur cette plate-forme trouveront :
- leurs homologues utilisant ces logiciels libres, avec leurs témoignages,
- les entreprises fournissant des services (maintenance, formation, support...),
- des indicateurs chiffrés permettant de comparer les solutions.
C'est un service de l'Adullact. En tant qu'utilisateur de Lizmap, vous pouvez :
- vous déclarer utilisateur
- y laisser un témoignage
- ajouter des copies d'écran
- lister les logiciels fonctionnant avec Lizmap
Vous trouverez aussi les fiches de :
WikidataWikidata [w] est une base de connaissances, libre, collaborative et multilingue, qui collecte des données structurées afin de fournir un support à Wikipédia, à Wikimedia Commons, aux autres wikis du mouvement Wikimedia, et à toute personne dans le monde.
Wikidata est un dépôt de stockage centralisé auquel tout le monde peut y accéder, comme les wikis gérés par la Wikimedia Foundation. Le contenu chargé dynamiquement à partir de Wikidata n'a pas besoin d'être maintenu dans chaque projet wiki individuel. Par exemple, les statistiques, les dates, les lieux et d'autres données courantes peuvent être centralisées dans Wikidata.
La fiche Lizmap de Wikidata contient les données principales, une description en anglais et français. Cette fiche peut-être complétée et la description traduite dans d'autres langues.
Vous trouverez aussi les fiches de :
René-Luc D'Hont
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11:00
3liz: Lizmap on the French interministerial open source software database
sur Planet OSGeoLizmap on the French interministerial open source software databaseLizmap is now referenced on the French interministerial open source software base (Socle interministériel de logiciels libres, SILL). You can consult the Lizmap software sheet. This file was created by a SILL referent: a public agent using Lizmap.
As an initial step to have this link, two articles must have been created beforehand : Lizmap on the Comptoir du libre and Lizmap on Wikidata.
French interministerial open source software databaseThe French interministerial open source software database (Socle interministériel de logiciels libres, SILL) is the reference catalog of free software recommended by the French State for the whole administration.
It is published by Etalab's open source software division (DINUM) on the code.gouv.fr website. Its management interface is accessible on the website sill.etalab.gouv.fr.
It is built in a collaborative way by a community of public agents, the SILL referents. As a public agent using Lizmap, you can become a Lizmap referent.
You will also find the sheets:
The comptoir du libreThe Comptoir du Libre lists the free softwares useful to the public services as well as their users and providers.
It's a free software marketplace. Its purpose is to share information about these softwares, and to put in contact the interested parties. The authorities browsing this platform will find :
- their counterparts using these free software, with their testimonies,
- companies providing services (maintenance, training, support...),
- numerical indicators allowing to compare the solutions.
The Comptoir du Libre is a service of Adullact. As a Lizmap user, you can:
- declare yourself a user
- leave a testimony
- add screenshots
- list software working with lizmap
You will also find the sheets:
WikidataWikidata [w] is a free, collaborative, multilingual, secondary database, collecting structured data to provide support for Wikipedia, Wikimedia Commons, the other wikis of the Wikimedia movement, and to anyone in the world.
Wikidata is a central storage repository that can be accessed by others, such as the wikis maintained by the Wikimedia Foundation. Content loaded dynamically from Wikidata does not need to be maintained in each individual wiki project. For example, statistics, dates, locations, and other common data can be centralized in Wikidata.
The Wikidata">[https:] Lizmap sheet contains the main data, a description in English and French. This sheet can be completed and the description translated into other languages.
You will also find the sheets:
René-Luc D'Hont
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11:00
CARTO Blog: A Recap of #SDSC22 London
sur Planet OSGeoHundreds of data scientists, developers, business leaders and academics from around the world attended the 2022 Spatial Data Science Conference in London this past May! Wit... -
9:11
gvSIG Team: Proyecto con gvSIG Online accésit en los premios Pedro R. Muro-Medrano
sur Planet OSGeoHoy queremos felicitar a Carles Martí Montolío que ha sido premiado con el accésit de la sexta edición de los premios Pedro R. Muro-Medrano, un galardón que reconoce los mejores trabajos de fin de estudios en el ámbito de las Infraestructuras de Información Geográfica y los estándares abiertos que las soportan.
El proyecto desarrollado por Carles, “Implementación del plugin ETL para la plataforma gvSIG online”, consiste en una serie de desarrollos orientados a automatizar tareas de transformaciones de datos, ya sean repetitivas o no, de manera que no sea necesario la manipulación de los datos a través de código. De esta manera, cualquier usuario será capaz de hacer una manipulación de los datos (geométricamente o no) o una homogeneización de datos que provengan de diferentes orígenes y formatos. Esto será posible gracias a un canvas que representará gráficamente el proceso de transformación de los datos de una manera fácil e intuitiva.
Más información sobre el premio aquí.
¡Felicidades Carles!
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8:00
Lutra consulting: Point cloud and QGIS 3D improvements - progress report 3
sur Planet OSGeoThis is a part of series of blog posts to update QGIS community with the outcome of the funding we had raised during late 2021 to improve elevation and point clouds in collaboration with North Road and Hobu. For other updates see part 1 and part 2.
Profile toolWith the new integrated profile tool, you can generate cross sections of point clouds, raster, vector and mesh data. For more information on this tool, you can see the excellent video introduction by North Road who implemented this part of the project.
To be able to view profiles from different data types, there is now a dedicated Elevation settings under layer properties. Users can set the elevation source, style and some other configurations. You can then enable elevation profile widget window by going to the main menu in QGIS, View > Elevation Profile.
Support for COPCCloud Optimized Point Cloud (COPC) is a new format for point cloud data and QGIS 3.26 comes with support for it (for both local files and data hosted on remote servers).
COPC is a very exciting addition to the ecosystem, because it is “just” a LAZ file (a format well established in the industry) that brings some interesting extra features. This means all software supporting LAZ file format will also be able to read COPC files without any extra development. If you are familiar with Cloud Optimized GeoTIFF (COG) for rasters, COPC is an extension of the same concept for point cloud data. Read more at [https:]
Ordinary LAS/LAZ files have an issue that it is not possible to efficiently read a subset of data without reading the entire file. This is less of an issue when processing point cloud data, but much more important for point cloud viewers, which typically show only a small portion of the data (e.g. zoomed in to a particular object or zoomed out to show the entire dataset). For that reason, viewers need to index (pre-process) the data before being able to show it - QGIS also needs to do the indexing when a point cloud file is first loaded. The new feature that COPC brings is that data is re-organized in a way that reading just some parts of data is efficient and easy. Therefore when loading COPC files, QGIS can immediately show them without any indexing (that takes time and extra storage).
In addition to that, COPC files can be efficiently used also directly from remote servers - clients such as QGIS can only request small portions of data needed, without the need to download the entire file (that can have size of many gigabytes). This makes dissemination of point cloud data easier than before - just make COPC files available through a static server and clients are ready to stream the data.
A small note: until now, QGIS indexed point cloud files to EPT format upon first load. From QGIS 3.26 we have switched to indexing to COPC - it has the advantage of being just a single file rather than lots of small files in a directory. If you have point cloud data indexed in EPT format already, QGIS will keep using EPT index (rather than indexing also to COPC).
Classified renderer improvementsClassified renderer for point clouds has been improved to:
- Show only classes that are in the dataset (instead of hard-coded list) & show also non-standard classes
- Show percentage of points for each class
- Work also for other attributes (return number, number of returns, point source and few other classes)
Vector transparency in 3D sceneThis improvement is not part of the crowdfunding campaign and was exclusively funded by the Swedish QGIS user group, but it is somehow relevant to the audience of this blog post!
With this feature, you can set polygon transparency in 3D scenes.
Want to see more features?We are trying to improve QGIS to handle point clouds for visualisation and analysis. If you would like certain features to be added to QGIS, do not hesitate to contact us on info@lutraconsulting.co.uk with your idea(s).
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10:17
gvSIG Team: Curso-concurso gvSIG Batoví amplía países participantes
sur Planet OSGeoEste año el curso-taller “Tecnologías de la Información Geográfica y gvSIG Batoví” da un paso más… Con el propósito de ampliar la experiencia uruguaya, en esta oportunidad la convocatoria se extiende a los docentes de Colombia y México. El curso va dirigido a docentes de enseñanza pre-universitaria de Geografía y áreas relacionadas con el conocimiento geográfico, ambiental y social.
gvSIG Batoví es un Sistema de Información Geográfica destinado a entornos educativos que surge como una adaptación del software libre desarrollado por la Asociación gvSIG.
La capacitación se llevará a cabo del 30 de junio al 29 de julio y tendrá modalidad b-learning (plataforma + taller por videoconferencia).
Con respecto al concurso, se llevará a cabo del 12 setiembre al 30 de noviembre (aproximadamente). Los equipos de trabajo estarán integrados por estudiantes y al menos un docente de referencia, el cual debió participar en alguna de las ediciones del curso. Cada equipo deberá presentar un proyecto de trabajo que identifique y aborde una problemática de interés local, posea una dimensión territorial y se enmarque en alguno de los Objetivos de Desarrollo Sostenible 2030 de la ONU.
Organizan, colaboran y participan:
Colombia: Instituto Geográfico Agustín Codazzi y Gobernación de Cundinamarca. México: Instituto Politécnico Nacional y Comisión Mexicana de Cooperación con la UNESCO (CONALMEX). Uruguay: Plan Ceibal, Dirección Nacional de Topografía (MTOP) e Inspección Nacional de Geografía y Geología (ANEP-DGES).
Enlaces de interés:
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9:58
How Big is Occupied Ukraine?
sur Google Maps ManiaThe New Statesman has released an interactive tool which allows you to view a map showing the area of Ukraine currently occupied by Russia. The map also allows you to drag this territory around the map so that you can easily compare this occupied area to any other location on Earth. If you drag the red polygon (representing the territory of Ukraine currently occupied by invading Russian forces)
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2:00
EOX' blog: mapchete Hub & dask
sur Planet OSGeoIn our previous post we briefly explained how we improved our processing pipeline for the new Sentinel-2 cloudless 2021 release. In this post we will go deeper into the details of what changed and where we are technologically. Parts of these developments are results from the LOOSE project funded by ...
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20:00
URL Map
sur Google Maps ManiaMap URL is an impressive interactive map which you can control by using a number of query string parameters within the map's URL address. Using the available query string parameters you can center your map at any location in the world, set the zoom level of the map and even add a marker at a specified location. For example the map in the screenshot above was created using the URL address: [https]
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12:14
iCarto Blog: Delimitation of hydrographic sub-basins using QGIS and a DEM
sur Planet OSGeoFreshwater is essential for life and development. For this reason, it is of vital importance to carry out a correct planning, management and analysis of this natural resource. The national and regional administrations of water of each country carry out this work (hydrological plans, characterization studies, monitoring of the water balance…). And to achieve this, the study, delimitation and preservation of river basins is essential.
The EU Water Framework Directive defines a hydrographic basin as “the area of land from which all surface run-off flows through a sequence of streams, rivers and, possibly, lakes into the sea at a single river mouth, estuary or delta”. The river basin as a resource management unit is considered indivisible. Each basin in turn is divided into sub-basins, these being defined as the area of land from which all surface run-off flows through a series of streams, rivers and,possibly, lakes to a particular point in a water course (normally a lake or a river confluence).
Work contextAt iCarto we have been working since 2012, first with the SIXHIARA project and later through the Blue Deal program, with the National Administration of Water Resources Management (DNGRH) and with the Regional Water Administrations (ARAs IP) of Mozambique. Among the actions, the creation of SIRH: Water Users and Licenses, the Water Resources Information System that is currently used by all the ARAs for the management of their licenses and water users, stands out.
This system used information from river and basin layers, created by the UDC’s Water and Environmental Engineering Group (GEAMA), but did not have a sub-basin layer. This type of information also did not exist in any of the national or regional administrations, being essential for proper planning and territorial management of water, especially in the country’s large basins. For all these reasons, the need to delimit the sub-basins of Mozambique was evident and the Dutch water authorities, through the Blue Deal program, decided to finance iCarto to carry out this activity.
The delimitation of sub-basins can be carried out through a hydrological analysis with a GIS application on a DEM (Digital Elevation Model). In our case we have used QGIS, a free open source GIS software, and the NASADEM global coverage model, since Mozambique does not have its own high-resolution model.
If you want to know more about the Digital Elevation Models and the process for the delimitation of sub-basins with QGIS in the following articles of this series you will find more information:
- Delimitation of hydrographic sub-basins using QGIS and a DEM (this post)
- Digital elevation models for hydrological studies
- Technical criteria for the delimitation of sub-basins
- Sub-basin delimitation process using QGIS
La entrada Delimitation of hydrographic sub-basins using QGIS and a DEM se publicó primero en iCarto.
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8:00
Lutra consulting: Point cloud and QGIS 3D improvements - progress report 3
sur Planet OSGeoThis is a part of series of blog posts to update QGIS community with the outcome of the funding we had raised during late 2021 to improve elevation and point clouds in collaboration with North Road and Hobu. For other updates see part 1 and part 2.
Profile toolWith the new integrated profile tool, you can generate cross sections of point clouds, raster, vector and mesh data. For more information on this tool, you can see the excellent video introduction by North Road who implemented this part of the project.
To be able to view profiles from different data types, there is now a dedicated Elevation settings under layer properties. Users can set the elevation source, style and some other configurations. You can then enable elevation profile widget window by going to the main menu in QGIS, View > Elevation Profile.
Support for COPCCloud Optimized Point Cloud (COPC) is a new format for point cloud data and QGIS 3.26 comes with support for it (for both local files and data hosted on remote servers).
COPC is a very exciting addition to the ecosystem, because it is “just” a LAZ file (a format well established in the industry) that brings some interesting extra features. This means all software supporting LAZ file format will also be able to read COPC files without any extra development. If you are familiar with Cloud Optimized GeoTIFF (COG) for rasters, COPC is an extension of the same concept for point cloud data. Read more at [https:]
Ordinary LAS/LAZ files have an issue that it is not possible to efficiently read a subset of data without reading the entire file. This is less of an issue when processing point cloud data, but much more important for point cloud viewers, which typically show only a small portion of the data (e.g. zoomed in to a particular object or zoomed out to show the entire dataset). For that reason, viewers need to index (pre-process) the data before being able to show it - QGIS also needs to do the indexing when a point cloud file is first loaded. The new feature that COPC brings is that data is re-organized in a way that reading just some parts of data is efficient and easy. Therefore when loading COPC files, QGIS can immediately show them without any indexing (that takes time and extra storage).
In addition to that, COPC files can be efficiently used also directly from remote servers - clients such as QGIS can only request small portions of data needed, without the need to download the entire file (that can have size of many gigabytes). This makes dissemination of point cloud data easier than before - just make COPC files available through a static server and clients are ready to stream the data.
A small note: until now, QGIS indexed point cloud files to EPT format upon first load. From QGIS 3.26 we have switched to indexing to COPC - it has the advantage of being just a single file rather than lots of small files in a directory. If you have point cloud data indexed in EPT format already, QGIS will keep using EPT index (rather than indexing also to COPC).
Classified renderer improvementsClassified renderer for point clouds has been improved to:
- Show only classes that are in the dataset (instead of hard-coded list) & show also non-standard classes
- Show percentage of points for each class
- Work also for other attributes (return number, number of returns, point source and few other classes)
Vector transparency in 3D sceneThis improvement is not part of the crowdfunding campaign and was exclusively funded by the Swedish QGIS user group, but it is somehow relevant to the audience of this blog post!
With this feature, you can set polygon transparency in 3D scenes.
Want to see more features?We are trying to improve QGIS to handle point clouds for visualisation and analysis. If you would like certain features to be added to QGIS, do not hesitate to contact us on info@lutraconsulting.co.uk with your idea(s).
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19:00
Data Spiders
sur Google Maps ManiaHub and Spoke is an interactive map which shows you the eight closest airports from any location on Earth. Click anywhere on this map and turf.js is used to draw lines from that location to the eight nearest airports. Obviously this map will be invaluable to anybody who is desperate to know where their nearest airports are located. However, to be honest, I think most people are going to use
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16:55
iCarto Blog: Delimitación de subcuencas hidrográficas usando QGIS y un MDE
sur Planet OSGeoEl agua dulce es fundamental para la vida y el desarrollo. Por ello es de vital importancia realizar una correcta planificación, gestión y análisis de este recurso natural. Las administraciones hidrológicas nacionales y regionales de cada país realizan este trabajo (planes hidrológicos, estudios de caracterización, seguimiento del balance hídrico…). Y para conseguirlo es imprescindible el estudio, delimitación y preservación de las Cuencas Hidrográficas.
La Directiva Marco del Agua de la UE define cuenca hidrográfica como la superficie de terreno cuya escorrentía superficial fluye en su totalidad a través de una serie de corrientes, ríos y eventualmente lagos hacia el mar por una única desembocadura, estuario o delta. La cuenca hidrográfica como unidad de gestión del recurso se considera indivisible. Cada cuenca a su vez se divide en subcuencas, definiéndose éstas como la superficie de terreno cuya escorrentía superficial fluye en su totalidad a través de una serie de corrientes, ríos y, eventualmente, lagos hacia un determinado punto de un curso de agua (generalmente un lago o una confluencia de ríos).
Contexto del trabajoEn iCarto llevamos trabajando desde 2012, primero con el proyecto SIXHIARA y después mediante el programa Blue Deal, con la Administración Nacional de Gestión del Recurso Hídrico (DNGRH) y con las Administraciones Regionales de Agua (ARAs IP) de Mozambique. Destaca entre las actuaciones la creación de SIRH: Usuarios de agua, el Sistema de Información del Recurso Hídrico que actualmente usan todas las ARAs para la gestión de sus licencias y usuarios de agua.
Este sistema usaba la información de las capas de ríos y cuencas, creadas por el grupo de investigación de Ingeniería del Agua y del Medio Ambiente (GEAMA) de la UDC, pero no contaba con una capa de subcuencas. Este tipo de información tampoco existía en ninguna de las administraciones nacionales ni regionales, siendo fundamental para realizar una correcta planificación y gestión territorial del agua, especialmente en las grandes cuencas del país. Por todo ello resultaba evidente la necesidad de delimitar las subcuencas de Mozambique y las autoridades holandesas del agua, a través del programa Blue Deal, decidieron financiar a iCarto para realizar esta actividad.
La delimitación de subcuencas se puede realizar mediante un análisis hidrológico con una aplicación SIG sobre un MDE (Modelo Digital de Elevaciones). En nuestro caso hemos utilizado QGIS y el modelo de cobertura mundial NASADEM, dado que Mozambique no dispone de un modelo de alta resolución propio.
Si quieres saber más sobre los Modelos Digitales de Elevaciones y el proceso para la delimitación de subcuencas con QGIS en los siguientes artículos de esta serie encontrarás más información:
- Delimitación de subcuencas hidrográficas con QGIS y MDE (este artículo)
- Modelos digitales de elevaciones para estudios hidrológicos
- Criterios técnicos para la delimitación de subcuencas
- Proceso de delimitación de subcuencas con QGIS
La entrada Delimitación de subcuencas hidrográficas usando QGIS y un MDE se publicó primero en iCarto.
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10:48
The Poor & Poor Health in Brussels
sur Google Maps ManiaThe investigative journalism magazine Médor has undertaken an extremely detailed examination of the health of Brussels. In Bruxelles Malade they explore the extreme inequality of health and health care provision in the capital of Belgium. Through a detailed analysis and mapping of health, economic and housing data Médor shows how the poorest neighborhoods in Brussels suffer from low incomes,
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10:00
Paul Ramsey: Who are the Biggest PostGIS Users?
sur Planet OSGeoThe question of “who uses PostGIS” or “how big is PostGIS” or “how real is PostGIS” is one that we have been wrestling with literally since the first public release back in 2001.
There is no doubt that institutional acceptance is the currency of … more institutional acceptance.
So naturally, we would love to have a page of logos of our major users, but unfortunately those users do not self-identify.
As an open source project PostGIS has a very tenuous grasp at best on who the institutional users are, and things have actually gotten worse over time.
Originally, we were a source-only project and the source was hosted on one web server we controlled, so we could literally read the logs and see institutional users. At the time mailing lists were the only source of project communication, so we could look at the list participants, and get a feel from that.
All that’s gone now. Most users get their PostGIS pre-installed by their cloud provider, or pre-built from a package repository.
So what do we know?
IGNIn the early days, I collected use cases from users I identified on the mailing list. My favourite was our first major institutional adopter, the Institut Géographique National, the national mapping agency of France.
In 2005, they decided to move from a desktop GIS paradigm for their nation-wide basemap (of 150M features), to a database-centric architecture. They ran a bake-off of Oracle, DB2 and PostgreSQL (I wonder who got PostgreSQL into the list) and determined that all the options were similar in performance and functionality for their uses. So they chose the open source one. To my knowledge IGN is to this day a major user of PostgreSQL / PostGIS.
GlobeXplorerThough long-gone as a brand, it’s possible the image management system that was built by GlobeXplorer in the early 2000’s is still spinning away in the bowels of Maxar.
GlobeXplorer was both one of the first major throughput use cases we learned about, and also the first one where we knew we’d displaced a proprietary incumbant. GlobeXplorer was one of the earliest companies explicitly serving satellite imagery to the web and via web APIs. They used a spatial database to manage their catalogue of images and prepared product. Initially it was built around DB2, but DB2 was a poor scaling choice. PostGIS was both physically faster and (more importantly) massively cheaper as scale went up.
RedFinRedFin was a rarity, a use case found in the wild that we didn’t have to track down ourselves.
They described in some detail their path from MySQL to PostgreSQL, including the advantages of having PostGIS.
Using PostGIS, we could create an index on centroid_col, price, and num_bedrooms. These indexes turned many of our “killer” queries into pussycats.
Google is not that big on promoting any technology they haven’t built in house, but we have heard individual Google developers confirm that they use core open source geospatial libraries in their work, and that PostGIS is included in the mix.
The biggest validation Google ever gave PostGIS was in a press release that recognized that the set of “users of spatial SQL” was basically the same as the set of “PostGIS users”.
Our new functions and data types follow the SQL/MM Spatial standard and will be familiar to PostGIS users and anyone already doing geospatial analysis in SQL. This makes workload migrations to BigQuery easier. We also support WKT and GeoJSON, so getting data in and out to your other GIS tools will be easy.
They didn’t address their new release to “Esri users” or “Oracle users” or “MySQL users”, they addressed it to the relevant population: PostGIS users.
More!Getting permission to post logos is hard. Really hard. I’ve watched marketing staff slave over it. I’ve slaved over it myself.
Major automaker? Check. Major agricultural company? Check. Major defence contractor? Check, check, check. National government? Check. State, local, regional? Check, check, check. Financial services? Check. Management consulting? Check.
Yes, PostGIS is real.
At some point, for a project with a $0 price point, you just stop. If a user can’t be bothered to do the due diligence on the software themselves, to reap all the advantages we offer, for free, I’m not going to buy them a steak dinner, or spoon feed them references.
That said! If you work for a major government or corporate institution and you are allowed to publicize your use of PostGIS, I would love to write up a short description of your use, for the web site and our presentation materials.
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12:00
Space Junk
sur Google Maps ManiaIn November Russia fired a missile at one of its own satellites, exploding it into over 1,500 pieces of large orbital debris and hundreds of thousands of pieces of smaller orbital debris. This debris caused pandemonium aboard the International Space Station, where the seven crew members were forced to shelter in capsules. Luckily (and purely by chance) the debris passed by the ISS without
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11:40
gvSIG Team: Curso taller: Análisis espacial y generación de mapas para identificar injusticias
sur Planet OSGeoEn breve estaremos dando un curso de la UNAM (gratuito) sobre geomática e injusticias.
CONTENIDOS:
Módulo Conceptual
a) Inequidades espaciales: conceptos básicos desde la geografía.
b) Justicia territorial: conceptos básicos desde las ciencias legales.
c) El marco conceptual y metodológico JUST-SIDE.
d) Soberanía tecnológica y software libre.Módulo Práctico: Herramientas de código abierto para el análisis espacial y la generación de mapas:
a) Plataforma gvSIG.
b) El uso de R para el análisis espacial.
c) Edición de mapas y en líneaRegistro abierto (hasta 16 de junio): [https:]]
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10:11
Wheat, War & Famine
sur Google Maps ManiaThe Guardian has published an informative story map which illustrates how the Russian invasion of Ukraine is disrupting the world's food supply and contributing to rising food prices across the world. In the Black Sea Blockade the newspaper uses a story map to illustrate and explain how the war in Ukraine is affecting the global supply of wheat and sunflower oil.Russia and Ukraine provide -
18:30
The Map of Your Twitter Friends
sur Google Maps ManiaSmall World is a new application which acts like a Marauder's Map for your Twitter Friends. Sign in to Small World using your Twitter account and you can view all the people you follow on Twitter on an interactive map. Small World can even automatically notify you when you're in the same city as one of your Twitter friends.According to Small World 14 of my Twitter friends are currently close-by
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15:40
The Latest on Cloud-Native Geospatial Standards in OGC
sur Open Geospatial Consortium (OGC)Tags: cloud-native geospatial, Member Meeting, OGC API, ogcapiI thought that it would be valuable to share an update of cloud-native geospatial activities in OGC, especially in light of our recent very successful Cloud-Native Outreach Event. This blog follows-up on the vision shared by OGC’s CEO, Dr. Nadine Alameh in April 2022 and two posts by OGC’s Visiting Fellow, Chris Holmes: Towards a Cloud-Native OGC and Towards a Cloud-Native Geospatial Standards Baseline.
For many years, OGC has been working on numerous aspects of the entire ecosystem of location data in cloud environments. Starting with Testbed 10 in 2013, OGC has been publishing engineering guidance on cloud topics, such as the Testbed 10 Performance of OGC® Services in the Cloud: The WMS, WMTS, and WPS cases. From those earliest efforts, OGC members have recognized that our approach to enabling cloud-native geospatial capabilities must be inclusive of this whole ecosystem: formats, services, architectures, and operations. I summarized this perspective at the Outreach Event discussing Advances in OGC Cloud-Native Geospatial Activities and will further elaborate in this blog post.
The cloud ecosystem is more than just the platform in which the data lives and is operated upon, but also includes: the algorithms to process information; interfaces between both humans and machines; formats to store and retrieve information; the security regime for content and access; business operations and revenue models to sustain the environments; regulatory oversight which may impact what enters or leaves the cloud; and much, much more. “Ecosystem” is truly the correct term as you can imagine an almost 1-for-1 analoge from the cloud to a natural ecosystem.
Building an EcosystemThe remainder of this blog digs into the elements of the ecosystem that OGC is addressing: interfaces, applications, encodings, and operations.
To start, we really cannot talk about geospatial in the cloud without also talking about the web: it is through web resources that so many users interact with cloud-hosted data and functions. OGC and the World Wide Web Consortium (W3C) collaborated in 2017 to publish the Spatial Data on the Web Best Practices as a means to illustrate how to make geospatial information more web-native. Web-native makes cloud-native more approachable. It is not enough to store data in the cloud in formats that improve access and analysis performance: we also need to develop APIs to discover, process, and extract information from the cloud and guide users to be able to work across cloud instances hosted by multiple providers. The impact of web-centric Standards modernization in OGC on enabling the cloud ecosystem cannot be overstated.
These APIs include OGC API - Features, foundational to accessing feature (vector) data as well as underpinning the STAC API specification, used for rapid discovery of remote sensing and other data. Extending the catalog paradigm, OGC API - Records allows discovery and access to all types of geospatial data as detailed as the record level. The architecture of these APIs allows developers to implement “just enough geo” to get to the data they need without becoming geospatial experts.
Many people identify the key use case for cloud-native capabilities to be the handling of massive data cubes, be those stacks of imagery or multidimensional scientific data sets. But just because you can store all of your data on the cloud does not mean that you want to use all of the data all of the time. OGC API - Environmental Data Retrieval (EDR) allows for complex subsetting of data cubes to return (or point to) just what is needed.
Do you need to fuse Internet of Things sensors with your massive content holdings? Leverage the OGC SensorThings API Standards. Consider that the combination of disparate data sources and dynamic sensors typically need some degree of processing to extract useful information, so implement OGC API - Processes to work between and within multiple data sets and feeds.
Processing comes in many models, but highly important these days is the use of Artificial Intelligence to distill vast quantities of data into useful information. OGC’s Artificial Intelligence in Geoinformatics (GeoAI) Domain Working Group is tackling some of the use cases and identifying targets for interoperability and even Standardization for information flow and quality. For example, the characterization of training and validation data used in GeoAI is now being standardized in the Training Data Markup Language for AI Standards Working Group. As part of this ecosystem, highly-automated data processing and analysis brings extraordinary benefits from cloud-native geospatial data.
The formats are also critically-important. I referenced a couple of blogs from Chris Holmes at the top of this post where there are excellent descriptions of several cloud-native encodings in wide (or soon to be wide) use. Understand that it is not just the structure of these encodings that make them “cloud-native,” but also the means by which the data are accessed (usually web-native, i.e., [HTTP).] Thus, many OGC-Standard encodings, such as GeoPackage, can be cloud-native. Below, I highlight several formats that are currently maturing in OGC.
OGC standardized GeoTIFF in 2019 and since that time, has been working to standardize Cloud Optimized GeoTIFF (COG) for management of raster data. Starting with the COG library, OGC has been working to document the format as a formal Standard and is nearing completion of this work. A draft specification is available as the OGC Testbed-17: Cloud Optimized GeoTIFF specification Engineering Report; the Standard won’t be too far behind.
More complex multidimensional data has proven to be efficiently encoded in the cloud using Zarr. Zarr is also in the final voting for endorsement as an OGC Community Standard. OGC’s most recently completed Testbed evaluated the suitability of Zarr for handling geospatial data cubes in the OGC Testbed 17: COG/Zarr Evaluation Engineering Report and Zarr did just fine… as did COG.
Feature (vector) data is already handled on the cloud in all types of databases that rely upon OGC Simple Features, OGC’s most widely-implemented Standard, to encode the geometry. But is this management really cloud-native, particularly with respect to streaming the data to users? Other encodings are being considered. GeoParquet is currently being incubated in OGC as a prospective cloud-native vector format. Other formats, such as FlatGeobuf are also being considered as potential Community Standards, to join existing Standards such as Indexed 3D Scene Layers and 3D Tiles, both of which offer cloud-natve capabilities, particularly with delivery of data.
Putting it together in the real worldYou have read this far and see a whole bunch of references to individual Standards and specifications that address specific parts of the cloud-native geospatial ecosystem. Putting it all together requires practical application of these technologies, Standards, and specs in concert. Operation of the cloud ecosystem requires coordination of many disciplines and sometimes new architecture designs relative to our past use of monolithic systems (such as microservices and highly-composable systems). This is where the other half of the OGC is so critical. The OGC Innovation Program operates numerous initiatives each year to experiment with or pilot the capabilities listed above against real-world scenarios and deliver documentation and examples that can be re-used for many use cases.
A search of “cloud” in the Engineering Report repository returns reference to 20 documents, each highlighting practical application of the capabilities highlighted above and more. These documents can be put in the context of the cloud-native ecosystem as illustrated below.
As you can see, the Innovation Program initiatives have touched upon many aspects of the cloud ecosystem, even if only peripherally related to location technology. These Engineering Reports reference even more work of relevance and identify specific practices that are portable across many use cases. I also recommend the recent OGC Best Practice for Earth Observation Application Package, which details packaging and deployment of Earth Observation Exploitation Platforms, generally to a cloud environment.
Development and MaturationIn summary, I’ve touched upon a lot of Standards and resources and there are many more in the OGC and through our partner organizations. Each, literally EACH, of these efforts requires considerable investment in time and resources. The dedication of OGC Members to advance this work is becoming increasingly represented in the cloud ecosystem. The fact that so many major cloud service providers (e.g., AWS, Google, Microsoft, Oracle) are OGC Members highlights the relevance of OGC’s efforts in this domain.
The Standards are being matured and we have expert guidance on deployment and management of the capabilities. Expect to see dedicated developer and implementer resources from the OGC to foster consistent use of geospatial content in cloud ecosystems. We will continue to research best practices, publish guidance, and identify capabilities offered by our members to sustain the entire location industry.
To see this work evolve in real time, be sure to attend the upcoming 123rd OGC Member Meeting in Madrid, Spain. More specifically, join our Developer Workshop on Friday, 17 June, 2022 hosted by Carto in downtown Madrid to code against the encodings, APIs, and more with experts from OGC and our member organizations.
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11:53
GeoSolutions: Free Webinar – First Steps with GeoNode 4.0
sur Planet OSGeoYou must be logged into the site to view this content.
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9:06
Scratch & Sniff New York
sur Google Maps ManiaUnder the grey, decrepit streets of New York there is a shiny, modern 21st Century city just waiting to emerge. At least there is on Chris Whong's Urban Scatchoff interactive map. Urban Scratchoff uses aerial imagery of early 20th Century New York, captured by a plane in a 1924 flyover of the city. Underneath this 20th Century aerial imagery is another layer which contains more recent aerial -
9:58
The Sound of 6,000 Years of Deforestation
sur Google Maps ManiaSix Thousand Years of Forests tells the story of how the UK's forests have been transformed over the last 6,000 years into croplands, pastures and cities. What was once a country covered by primeval forest is now an intensely farmed and populated landscape, with only 13% of the country covered by woodland. However Six Thousand Years of Forests doesn't confine itself just to the UK. In fact it
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4:02
Sean Gillies: Long run peanut butter and honey sandwich
sur Planet OSGeoIn a 12-hour race I will expend much more energy than I store in my body in the form of glycogen. I continue to work on training my body to digest solid food that has a good mix of carbs, fat, and protein while on the go. In a race I'll eat pieces of a ham and cheese wrap, a quesadilla, or even bacon when it's available. On my long weekend runs, which are now up to three hours or more, each, I'm taking a big peanut butter and honey sandwich. The ingredients:
2 slices whole wheat bread (Dave's Good Seed (TM))
A generous spread of peanut butter, same weight as a slice of bread
More honey, 50% more than the weight of a slice of bread. Slightly crystalized honey is good because it doesn't immediately run off the slice.
This makes a sandwich containing about 700 calories. I cut it into four pieces and stuff all into a small rectangular ziploc container the night before. Each piece has ~20 more calories than a Honey Stinger waffle and zero waste per serving.
I've been eating peanut butter and honey sandwiches for over 50 years, as long as I can remember. It was always honey in my family, not jam or jelly, though I love that as well. And when I was a kid it was always Miller's Honey.
With the help of his pioneer father, Nephi exchanged five bags of oats for seven colonies of bees. This was the beginning of Miller's Honey Company.
A little extra salt sprinkled on the peanut butter is good
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20:45
Markus Neteler: GRASS GIS 8.2.0 released
sur Planet OSGeoThe 8.2.0 release of GRASS GIS is now available with results from the GSoC 2021 and many other additions. A new grass.jupyter package is now included for interacting with Jupyter notebooks. Single window graphical user interface is available in GUI settings. r.series and three other modules are newly parallelized. Additionally, the release includes a series of scripting, packaging, and reproducibility improvements.
For all 220+ changes, see our detailed announcement with the full contributors and list of features and bugs fixed at GitHub / Releases / 8.2.0. Special thanks to GSoC students, their mentors, and first-time contributors!
Packages and installers are now available for Windows, macOS, Debian, Fedora, and Gentoo with more coming soon.
See more at grass.osgeo.org / News.
The post GRASS GIS 8.2.0 released appeared first on GFOSS Blog | GRASS GIS and OSGeo News.
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17:25
GRASS GIS: GRASS GIS 8.2.0 released
sur Planet OSGeoWhat’s new in a nutshell The 8.2.0 release of GRASS GIS is now available with results from the GSoC 2021 and many other additions. A new grass.jupyter package is now included for interacting with Jupyter notebooks. Single window graphical user interface is available in GUI settings. r.series and three other modules are newly parallelized. Additionally, the release includes a series of scripting, packaging, and reproducibility improvements. Full list of changes and contributors For all 220+ changes, see our detailed announcement with the full list of features and bugs fixed at GitHub / Releases / 8.
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9:49
The Noise of the City
sur Google Maps ManiaNoisy Cities is an interactive map which visualizes noise pollution in New York, Paris and London.Noisy Cities isn't just a mapped visualization of noise pollution. It is also a mapped sonification of noise pollution. These interactive maps of New York, Paris and London don't just use a heat map layer to visualize the average levels of road traffic and aircraft noise. If you turn on your
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22:43
Fernando Quadro: Preciso usar o GeoServer?
sur Planet OSGeoA resposta simples é que você não precisa dele, mas ele torna a sua vida muito mais fácil.
Isso porque você precisa ter algum tipo de elemento entre seu banco de dados e a sua aplicação, seja ela desktop, web ou mobile.
Então você pode escrever seu próprio servidor de mapas em PHP (Java, Python, NodeJS ou qualquer outra linguagem) e com isso lidar com todos os “caprichos” do banco de dados que você estiver usando e resolver o “problema” dos diversos formatos de entrada e saída, fazer depuração, testes, e etc.
E isso sem falar dos padrões adotados pelo GeoServer que permite que qualquer pessoa que possa implementar o padrão consuma seus mapas em seu cliente sem qualquer codificação extra de sua parte.
Ou você pode usar o GeoServer e começar a servir mapas em poucas horas.
Quer aprender a disponibilizar seus mapas com o GeoServer? O Curso de GeoServer está com inscrições abertas.
Conheça agora mesmo a Geocursos e garanta a sua matrícula no curso de Geoserver!
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23:12
GRASS GIS: Results of the GRASS GIS student grants - Part 2
sur Planet OSGeoCaitlin’s path in her own words Enhancing GRASS GIS integration with Jupyter Notebooks I began contributing to GRASS GIS last year during Google Summer of Code (GSoC) 2021. As a second-year doctoral student at North Carolina State University (NCSU) in the GeoForAll Lab, I was taking a lot of courses that used GRASS GIS and other OSGeo software. I’m interested in geo-visualization, open-source software development and making powerful geospatial tools accessible to everyone.
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10:57
Where Cars Kill
sur Google Maps ManiaEvery year tens of thousands of people are hit by cars in New York. The New Yorker has released an interactive map which allows you to see where cars have injured pedestrians or cyclists between 2013 and 2021. Enter a New York zip-code into the When Cars Kill map and you can view the locations of all the car crashes in that neighborhood that resulted in injuries.The map uses data from the New
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11:12
geomati.co: FlatGeobuf: eficiencia serverless
sur Planet OSGeoFlatBuffers es un formato de datos creado por Google que permite serializar sin parsear ni desempaquetar. Esto lo convierte en un formato idóneo para streaming, por su eficiencia de memoria y velocidad.
FlatGeobuf es la versión geoespacial de FlatBuffers, que permite almacenar una colección de Simple Features. En la versión 3.1 GDAL ha sacado un driver FlatGeobuf — GDAL documentation que permite acceder a los datos en este formato.
El acceso a los datos mediante el uso del índice espacial optimizado para la lectura remota hace que podamos desplegar estos archivos en un CDN y consumirlos directamente sin necesidad de servidor de mapas: una arquitectura totalmente serverless.
Transformando .gpkg en FlatGeobuf (.fgb) vía GDALRecientemente hemos publicado una prueba de concepto que demuestra las ventajas de FlatGeobuf: a partir de los edificios del Catastro hemos descargado los edificios de Oviedo utilizando nuestro Catastro Inspire Downloader y posteriormente los hemos transformado en .fgb vía ogr2ogr.
Conversión del dato de .gpkg a .fgb (GDAL > 3.1)
ogr2ogr -f FlatGeoBuf buildings_Territorial_office_33_Oviedo.fgb buildings_Territorial_office_33_Oviedo.gpkg -sql "SELECT * FROM Building"
Para un rendimiento óptimo se recomienda la publicación en un CDN pero usamos nuestros servidores para esta prueba de concepto.
Publicando con MapboxGLA partir de ahí hemos desarrollado un visor ligero basado en MapboxGL que se alimenta de este FlatGeobuf y lo muestra, además de permitir disolver geometrías pinchando en edificios contiguos (como prueba de la versatilidad del formato):
- demo: Flatgeobuf POC
- código fuente visor: [https:]]
La potencia de este formato de archivo es que a partir del índice espacial podemos recuperar datos bajo demanda. Si inspeccionáis las llamadas desde la pestaña de red de vuestros navegadores en modo desarrollo veréis las diferentes llamadas que hace para la descarga del dato.
La diferencia con los vector tiles (teselas vectoriales) es que se está accediendo al dato original manteniendo las relaciones y sin simplificaciones. Si probáis a pinchar sobre una geometría podréis ir disolviéndolas con las contiguas.
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9:39
Prevailing Winds & Runway Alignment
sur Google Maps ManiaWind History is a new interactive map which shows the prevailing wind directions around weather stations in the United States. Most of these weather stations are located at airports. On the map 2,500 wind rose diagrams show the normal wind direction at airports across the United States. A larger date control allows you to view the prevailing wind directions at all airports on the map for any
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11:00
CARTO Blog: How ASDA Uses Location Intelligence for Site Selection
sur Planet OSGeoOne of the most important decisions retailers can make revolves around the site selection component within their network expansion plans. Afterall, at the end of the day, t...
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10:13
The Top 10 Wordle Like Map Games
sur Google Maps ManiaThe pace of new Wordle inspired map and geography games shows no signs of abating. EOGuesser is the latest daily geography challenge which is obviously inspired in part by the now famous word game. The objective of EOGuessser is to guess the correct location shown in a satellite image. You have three attempts to guess the correct location. The closer you get to the correct location the more
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0:06
Le blog de Geomatys: Marketing Intern (H/F)
sur Planet OSGeoWe are in search of a marketing specialist (M1, M2 or equivalent) with a focus on international business and/or innovations for application to a thematic subsidiary in the health sciences and digital technology domains.
At Geomatys, you will have the opportunity to contribute to defining the company’s marketing strategy, and your first project will be to conduct market research and assist with branding and positioning of an operational disease epidemiology product on the global market. You will be learning from top disease scientists, geospatial data engineers, and software developers to launch this exciting project with deep societal impact. We need your help and business knowledge to shape our message and grow our client base.
The ideal candidate should possess :
- Curiosity.
- Willingness and capacity to work collaboratively with scientists developing the products on offer.
- Drive for success.
- Methodological rigor and accountability.
- Meticulous organization skills.
- Both internal (team-facing) and external (client-facing) communication skills.
If you are enthusiastic about shaping and communicating the vision of an ultra-innovative technology company with a high impact subsidiary, send your CV to Isabelle Pelissier (isabelle.pelissier@geomatys.com). No need for a cover letter, just your CV and any links to projects you’ve contributed to (websites, reports, etc.).
Position to be carried out in Montpellier, France.
Ideally, the position will be filled by a part-time student completing their studies at a French academic institution (“alternance”) or by a paid internship (stage) of 6 months. There may be an opportunity to extend or resume the work after this period.
Who are we ?
GEOMATYS is a software development and company that has been developing products and new information systems to process geographic information for 18 years. We process, analyze, and communicate large volumes of geographic information, which we then integrate for the needs of our customers. We are a company influenced by the strong technical culture of our leadership teams, developing innovative projects for industry and scientists in fields as varied as the Environment, Space or Defense. Thanks to the recognition of our work in research and development, our company, GEOMATYS, has gained expertise working with major clients (Naval Group, Airbus, CNES, etc).
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12:55
GeoSolutions: GeoSolutions presente ad ASITA 2022
sur Planet OSGeoYou must be logged into the site to view this content.
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11:57
What Matters in the Midterm Elections
sur Google Maps ManiaIn order to find out which issues voters care most about for the upcoming midterms, Axios analyzed which issues were being searched the most on Google in each congressional district. In Midterm elections 2022: The issues that matter to Americans Axios has mapped out the relative and absolute importance of different political issues in each district.As you can see in the animated screenshot -
8:31
Map Clipping
sur Google Maps ManiaI recently received a request to help design a triangular map to complement a company logo. Having only last week written about Microsoft's Building Footprints I decided that I would use a building footprint layer as my base-map, with the map clipped to only show those buildings within a triangular area. The objective being to create something like the map above.Having downloaded the building
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21:24
Martin Davis: Algorithm for Concave Hull of Polygons
sur Planet OSGeoThe previous post introduced the new ConcaveHullOfPolygons class in the JTS Topology Suite. This allows computing a concave hull which is constrained by a set of polygonal geometries. This supports use cases including:
- generalization of groups of polygon
- joining polygons
- filling gaps between polygons
A concave hull of complex polygons
The algorithm developed for ConcaveHullOfPolygons is a novel one (as far as I know). It uses several features recently developed for JTS, including a neat trick for constrained triangulation. This post describes the algorithm in detail.
The construction of a concave hull for a set of polygons uses the same approach as the existing JTS ConcaveHull implementation. The space to be filled by a concave hull is triangulated with a Delaunay triangulation. Triangles are then "eroded" from the outside of the triangulation, until a criteria for termination is achieved. A useful termination criteria is that of maximum outside edge length, specified as either an absolute length or a fraction of the range of edge lengths.
For a concave hull of points, the underlying triangulation is easily obtained via the Delaunay Triangulation of the point set. However, for a concave hull of polygons the triangulation required is for the space between the constraint polygons. A simple Delaunay triangulation of the polygon vertices will not suffice, because the triangulation may not respect the edges of the polygons.
Delaunay Triangulation of polygon vertices crosses polygon edges
What is needed is a Constrained Delaunay Triangulation, with the edge segments of the polygons as constraints (i.e. the polygon edge segments are present as triangle edges, which ensures that other edges in the triangulation do not cross them). There are several algorithms for Constrained Delaunay Triangulations - but a simpler alternative presented itself. JTS recently added an algorithm for computing Delaunay Triangulations for polygons. This algorithm supports triangulating polygons with holes (via hole joining). So to generate a triangulation of the space between the input polygons, they can be inserted as holes in a larger "frame" polygon. This can be triangulated, and then the frame triangles removed. Given a sufficiently large frame, this leaves the triangulation of the "fill" space between the polygons, out to their convex hull.
Triangulation of frame with polygons as holes
The triangulation can then be eroded using similar logic to the non-constrained Concave Hull algorithm. The implementations all use the JTS Tri data structure, so it is easy and efficient to share the triangulation model between them.
Triangulation after removing frame and eroding triangles
The triangles that remain after erosion can be combined with the input polygons to provide the result concave hull. The triangulation and the input polygons form a polygonal coverage, so the union can be computed very efficiently using the JTS CoverageUnion class. If required, the fill area alone can be returned as a result, simply by omitting the input polygons from the union.
Concave Hull and Concave Fill
A useful option is to compute a "tight" concave hull to the outer boundary of the input polygons. This is easily accomplished by removing triangles which touch only a single polygon.
Concave Hull tight to outer edges
Concave Hull of complex polygons, tight to outer edges.
Like the Concave Hull of Points algorithm, holes are easily supported by allowing erosion of interior triangles.
Concave Hull of Polygons, allowing holes
The algorithm performance is determined by the cost of the initial polygon triangulation. This is quite efficient, so the overall performance is very good.
As mentioned, this seems to be a new approach to this geometric problem. The only comparable implementation I have found is the ArcGIS tool called Aggregate Polygons, which appears to provide similar functionality (including producing a tight outer boundary). But of course algorithm details are not published and the code is not available. It's much better to have an open source implementation, so it can be used in spatial tools like PostGIS, Shapely and QGIS (based on the port to GEOS). Also, this provides the ability to add options and enhanced functionality for use cases which may emerge once this gets some real-world use.
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15:13
GeoTools Team: GeoTools 27.0 Released
sur Planet OSGeoThe GeoTools team is pleased to share the availability GeoTools 27.0 : geotools-27.0-bin.zip geotools-27.0-doc.zip geotools-27.0-userguide.zip geotools-27.0-project.zip Improvements and fixes in this release New Feature GEOT-7104 Clarify GeoTools.init() workflow and logging setup and configuration GEOT-7100 Migrate Log4JLoggerFactory to reload4J library GEOT-7099 Introduce
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10:51
Footways and Slow Ways
sur Google Maps ManiaA new interactive map can help you navigate London on foot, showing you the quietest and most enjoyable routes for walking in the capital. The Footways map includes hundreds of kilometres of scenic, safe and pedestrian-friendly walking routes in central London.The map includes hundreds of routes, spanning out from London's mainline stations, using the most low-traffic and low-pollution streets,
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23:29
Sean Gillies: Superior training week nine recap
sur Planet OSGeoWhat a crappy week for America, a country where half the residents think that the root of the school shooting crisis is not guns, but too many school entrances and exits. America is sick and it feels like it's getting worse, not better. I escaped into trail running: six runs on six days, one hill interval workout on Towers Trail, and back-to-back long runs in the foothills of the Rockies on Saturday and Sunday. Here are the numbers.
11 hours, 5 minutes
50.5 miles
8,582 ft D+
Saturday I went out intending to do two and a half climbs of Horsetooth and Arthurs Rock. After about seven miles I started feeling pain in my right shin, just above my ankle. It gradually increased and so I stopped at 13 miles and skipped the last climb. Evidently it was not a stress fracture because I was able to hike and run with no pain today. Only an irritated tendon, I think. My new-ish Speedgoat 5s are not a great fit my slightly smaller right foot, perhaps my ankle tendons were fighting a loose fit.
Today I wore my newest pair of the Speedgoat 4, deployed my hiking sticks, and reached the summit of Crosier Mountain (9,257 ft) just before the first thunderstorms developed. I've never been up this trail before. It's a wonderful mix of steep switchbacks and highly runnable singletrack. There's not a lot of shade and no water to speak of, so it could be grueling on a hotter day. I felt great and got to the top in a respectable time. This was my first run over 8,000 ft in 2022. I'll be doing more of this as the snow recedes. There's still quite a bit above 10,000 ft.
Stretch of runnable singletrack between miles one and two
View of Rocky Mountain National Park from Crosier Mountain, 9257 ft.
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21:12
GRASS GIS: Results of the GRASS GIS student grants - Part 1
sur Planet OSGeoLinda’s path in her own words From enhancing first time user experience to Single-Window in GRASS GIS I started contributing to GRASS GIS in the summer of 2020 as part of the Google Summer of Code (GSoC) project “Creation of a new GRASS GIS startup mechanism”, which I applied for as a complete programming illiterate. Although I felt a bit clumsy at first, with the great help of my mentors, I managed to significantly improve the GRASS data catalog. -
13:59
pycsw Team: pycsw May 2022 code sprint report
sur Planet OSGeopycsw May 2022 code sprint reportThe second pycsw code sprint was held on 23 - 25 May 2022. The sprint was held virtually (Jitsi/Gitter) and involved collaboration between both users and developers. A number of areas were discussed and addressed, which are elaborated on in detail below.
- CSW Federated search fixes: issue 729 was tested and validated
- OWSLib ISO constraint parsing: testing and discussion of OWSLib PR 799
- XSLT support: implementation of issue 761 in
- SOLR repository backends: initial SOLR backed support was implemented in [https:]]
- JSON storage: as per issue 704, initial JSON support was implemented along with an OGC API - Records parser / ingest
- Security, access control and transactions:
More information on the sprint can be found on the pycsw wiki.
Thank you to everyone who contributed their time/resources/facilities to the sprint - see you in Florence at FOSS4G 2022!
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14:39
The Highway Exits of Massachusetts
sur Google Maps ManiaThe animated GIF above shows aerial images of highway exits across Massachusetts. The images were taken from Bird's Eye Cards, a collection of categorized aerial observations of the Massachusetts landscape, created by the Leventhal Map & Education Center at the Boston Public Library. Lots of round water bodies in Massachusetts Bird's Eye Cards was created by Garrett Dash Nelson, who has -
10:27
America's Mass Shooting Problem
sur Google Maps ManiaSchool Shootings are an almost uniquely American problem. While it is true that school shootings have taken place in other countries around the world, as the map above shows no other country has experienced anywhere near the number of school shootings as the United States. This School Shootings by Country 2022 map claims that the USA has experienced 288 school shootings. The country with the -
10:34
Polluting the Poor in San Francisco
sur Google Maps ManiaIf you are on a low income in San Francisco then you are probably breathing polluted air. On average the poorest San Franciscans have a 30% higher exposure to nitrogen dioxide than other residents in the city. If you are poor and black then you are probably breathing in even more polluted air. Neighborhoods with high densities of Black, Latino and Asian residents have on average 55 percent more
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10:05
GeoSolutions: GeoStory: A powerful feature for GeoNode
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