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I have a set of Lat/Lon points and I'd like to know the actual ground elevation of these points. I have access to Global Mapper, Google Earth, AutoCAD Civil 3D. Could somebody suggest the bets way to go about doing this. I'm trying to compare the recorded elevations from a GPS model (at the ground) to actual "ground-truth" (obviouslly based on some sort of terrain set)

Thanks

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In Global Mapper, bring in your points and a DEM (digital elevation model) which can be downloaded in varying resolutions. Select your points with the digitizer tool and right click one of them. Under "Analysis/Measurement" there is an option to "Apply Elevations from Terrain Layer to Selected Features." This will append the value from the DEM to the attribute table of the points. You can then export these in a file format you like for the attribute table (I typically like shapefiles).

You won't get real "ground truth" by doing it this way. GIS typically utilizes fairly generalized elevation data. The only way to be absolutely sure about "ground truth" is to hire a surveyor to measure each point, but this will give you a pretty good idea.

example from Global Mapper

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How many points do you have? Do you have access to some good elevation data?

One options is to use the Google Elevation API [(free) API key suggested] if you don't have [or, like me, can be too lazy to get] quick access to a DEM or other good elevation data. Note that the DEM resolution will most likely be less than what you can download, but if you are just trying to see how far off your GPS is that might be fine. It will give you the lat/long as well as the elevation (meters) and the resolution of the DEM, which is nice. If you need a point: http://maps.googleapis.com/maps/api/elevation/json?locations=39.7391536,-104.9847034&sensor=false

If you are looking at a path or a slew of points in succession: https://developers.google.com/maps/documentation/elevation/#Paths

I once compared my sub-meter horizontal GPS handheld data with some LIDAR data and had huge differences in some areas, so hopefully you're not using the GPS vertical for anything too accurate.

While the link above works fine for me, Google encourages you to use the API for access - more info below
https://developers.google.com/maps/documentation/elevation/#api_key

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