Adjusting the Elevation data of a DEM to the elevations of another DEM.
Dionybell
Global Mapper UserTrusted User
Hello. I have two DEM (Geotiff files) of the same surface. The thing is, one of them is from 2011 and the new one is 2014. I want to measure the difference between volumes.
Problem is, the elevations of both DEMs are different. The one of 2011 used an geoid model (EGM08) for the datum. The new DEM was obtained from an UAV mission (photogrametry) but didn't use the geoid as a datum. The slopes are real, but the values are different.
The thing I want to do is to adjust the "bad" DEM to the correct one and THEN calculate volume differences.
I checked the option of Alter Elevations, but couldn't use that. Then I checked Combine/Compare Terrains and I think I can't use that either.
Any options that I have? Sorry for my english.
Thanks in advance.
Problem is, the elevations of both DEMs are different. The one of 2011 used an geoid model (EGM08) for the datum. The new DEM was obtained from an UAV mission (photogrametry) but didn't use the geoid as a datum. The slopes are real, but the values are different.
The thing I want to do is to adjust the "bad" DEM to the correct one and THEN calculate volume differences.
I checked the option of Alter Elevations, but couldn't use that. Then I checked Combine/Compare Terrains and I think I can't use that either.
Any options that I have? Sorry for my english.
Thanks in advance.
Comments
-
Is the DEM of a relatively small area so that the difference in the geoid models is basically constant over the area? If so you can use the Alter Elevations tab of the Options dialog to apply that fixed offset to get them on the same geoid, then use the Analysis menu command to measure volume between surfaces to get the volume..
If you aren't sure you might use the Combine/Compare Terrains to subtract the surfaces. Assuming much of the area is unchanged there should be a near constant offset between the 2 surfaces that you could use to derive the offset.
For a more complete and automated solution you can also get the Geographic Calculator from Blue Marble (Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation) and then you can enable 'GeoCalc Mode' in Global Mapper and use Geographic Calculator for full geoid conversions right in Global Mapper. Contact sales@bluemarblegeo.com for information about that solution.
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation -
Is the DEM of a relatively small area so that the difference in the geoid models is basically constant over the area? If so you can use the Alter Elevations tab of the Options dialog to apply that fixed offset to get them on the same geoid, then use the Analysis menu command to measure volume between surfaces to get the volume..
If you aren't sure you might use the Combine/Compare Terrains to subtract the surfaces. Assuming much of the area is unchanged there should be a near constant offset between the 2 surfaces that you could use to derive the offset.
For a more complete and automated solution you can also get the Geographic Calculator from Blue Marble (Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation) and then you can enable 'GeoCalc Mode' in Global Mapper and use Geographic Calculator for full geoid conversions right in Global Mapper. Contact sales@bluemarblegeo.com for information about that solution.
Thanks,
Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
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