GreatCircleDistance( )

Purpose

Calculates distance along great circle route between two points.

*Author*	*Date of code (original)*	*Updated on*	*Date of page (original)*	*Updated on*
Bill Thoen bthoen@ctmap.com	29Dec2000	29Dec2000	5Jan2001	10Jan2001

Restrictions on use

This module is distributed under the terms of the Lesser GNU General Public License. Restrictions on the use of this work in a commercial application or derivative work is described in the Lesser GNU General Public License page at: http://www.fsf.org/copyleft/lesser.html

Description

Returns the great circle distance between two points. Distance units are the same as those of the radius. This is equivalent to MapInfo's Distance() function.

External resources

none

Declare statement of sub_function. Include in your program. Copy/Paste if needed.

declare function GreatCircleDistance (
   byval fLon0 as float,    'Origin longitude
   byval fLat0 as float,    'Origin latitude
   byval fLon1 as float,    'Destination longitude
   byval fLat1 as float,    'Destination latitude
   byval fRadius as float t  'Radius of earth
   ) as float

Returned value(s) (function only)

distance in the same units as the earth radius

Other required declare statement(s). Include in your program. Copy/Paste if needed.

include "GC_Constants.def"
include "GC_Distance.def"

MapBasic Code. Copy/Paste if needed.

View code in separate window

Availability for download

GreatCircleFn.zip

Example

include "GC_Constants.def
include "GC_Distance.def"

dim fLat0, fLon0, fLat1, fLon1 as float
dim fDistance as float

   fLat0 = 40 fLon0 = -105
   fLat1 = 42 fLon1 = -72

   fDistance = GreatCircleDistance (fLon0, fLat0, fLon1,
      fLat1, EARTH_RADIUS)

Comments

By default, the EARTH_RADIUS constant is set to 3958.75 (miles). To use kilometers or some other measure, comment and uncomment the appropriate lines in GC_Constants.def. GreatCircleDistance() produces identical results as MapInfo's spherical distance function when you set the earth's radius to 3958.75 and use miles as the distance units. However, unlike MapInfo's function, this can be used for different sized spheres such as other planets.