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I've done the method of downloading a DEM from a database, generate contours on Global Mapper, QGIS or ArcGis, and upon exporting them to DXF, I can open them on Civil 3D and build a surface, but the base elevation starts from 0m so I can't work with that since I need the real elevation to match my field work.

I've also tried doing it with Google Earth by building a path, saving that to .kml, make that into coordinates and elevation data through GPS Visualizer and then making a DEM from that on the above mentioned software, but this way I can only generate contours and visualize them properly as vectors, but upon generating a surface from them the coordinates, elevation and size are all over the place.