[gdal-dev] Use gdalwarp to convert DTM from EGM96 geoid to WGS84 ellipsoid height

[Daniel Jacobs]

I want to convert my DTM geotiff file from height above geoid to height above ellipsoid.

I've tried the following command (among numerous similar commands):

    gdalwarp -overwrite in_dem.tif out_dem.tif -s_srs EPSG:4326+5773 -t_srs EPSG:4979


I have files egm96_15.gtx​ and us_nga_egma96_15.tif​ in my /usr/share/proj​ resource directory, and PROJ_LIB​ is set to /usr/share/proj​.

This transform works:

    $gdaltransform -s_srs EPSG:4326+5773 -t_srs EPSG:4979
    Enter X Y [Z [T]] values separated by space, and press Return.
    10 20 0
    10 20 26.504430770874

But the output file of gdalwarp​ is never different from the input file, no matter what I try. Is it because the file is a DTM instead of a DEM?


Thanks!

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