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<pre>I want to convert my DTM geotiff file from height above geoid to height above ellipsoid.</pre>
<pre>I've tried the following command (among numerous similar commands):</pre>
<pre> gdalwarp -overwrite in_dem.tif out_dem.tif -s_srs EPSG:4326+5773 -t_srs EPSG:4979
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<pre style="background-color:rgb(255, 255, 255)">I have files <code>egm96_15.gtx</code> and <code>us_nga_egma96_15.tif</code> in my <code>/usr/share/proj</code> resource directory, and <code>PROJ_LIB</code> is set to <code>/usr/share/proj</code>.</pre>
<pre style="background-color:rgb(255, 255, 255)">This transform works:</pre>
<pre style="background-color:rgb(255, 255, 255)"> $gdaltransform -s_srs EPSG:4326+5773 -t_srs EPSG:4979<div style="margin:0px"> Enter X Y [Z [T]] values separated by space, and press Return.</div><div style="margin:0px"> 10 20 0</div> 10 20 26.504430770874</pre>
<pre style="background-color:rgb(255, 255, 255)">But the output file of <code>gdalwarp</code> is never different from the input file, no matter what I try. Is it because the file is a DTM instead of a DEM?</pre>
<pre style="background-color:rgb(255, 255, 255)"><br></pre>
<pre style="background-color:rgb(255, 255, 255)">Thanks!</pre>
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