DEM vs. Raster Topo Map
Daniel Hegyi-Purice
Global Mapper User
My issue is that the DEM elevation data is not the same with the elevation information from my topo map. For the same point, DEM is showing 200 m and topo map 175 m. What can cause this difference?
Comments
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There could be a number of causes for that, but the most likely is that they are on different vertical reference systems. Do you know what the heights in the DEM and your topo map are relative to? One might be sea level and the other the WGS84 ellipsoid, or a host of different vertical datums.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
My topo map is relative to Black Sea (Stereo 70) and the DEM to WGS84.
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Those are the horizontal datums, the vertical datum is a completely different thing. However it's possible the heights are just relative to the ellipsoid, so one could have heights relative to the WGS84 ellipsoid and the other relative to the Krassovsky ellipsoid (I think), so there could be differences there. See http://www.ngs.noaa.gov/datums/vertical/VerticalDatums.shtml for more information on vertical datum systems.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com
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