<div dir="ltr"><div><div><div><div>I try to perform a vertical transformation from WGS84 ellipsoid heights to geoid MSL heights on a Geotiff with a geoid GTX raster translated from Geotiff.<br><br>gdalwarp -overwrite -s_srs "+proj=longlat +datum=WGS84 +no_defs +geoidgrids=C:\TEMP\gr20006g06.gtx" -t_srs EPSG:4326 -r bilinear -of GTiff C:/TEMP/gimdem1_1_epsg4326.tif C:/TEMP/gimdem1_1_epsg4326_geoid.tif<br><br><font size="1"><font size="2">The transformation runs, but there are no changes in cell values of the output raster as expected. <br></font></font></div><div><font size="1"><font size="2">I can do a gdal_calc between the input raster and the geoid raster to an output raster, which changes the pixel values, but requires a number of previous steps: align, clip, warp, resampling of the geoid raster.<br></font></font></div><div><font size="1"><font size="2"><br></font></font></div><div><font size="1"><font size="2">I would think the +geoidgrids warping is the most correct?<br></font></font></div><div><font size="1"><font size="2"><br>How can I change my data or my gdalwarp flags and inputs to do a transformation which actually use the geoid grid?<br></font></font></div><div><font size="1"><font size="2"><br></font></font></div><div><font size="1"><font size="2">Some information on the input DEM and geoid:<br></font></font></div><br>Input DEM:<br><font size="1">Driver: GTiff/GeoTIFF<br>Files: C:/TEMP/gimdem1_1_epsg4346.tif<br>Size is 14727, 9815<br>Coordinate System is:<br>GEOGCS["WGS 84",<br> DATUM["WGS_1984",<br> SPHEROID["WGS 84",6378137,298.257223563,<br> AUTHORITY["EPSG","7030"]],<br> AUTHORITY["EPSG","6326"]],<br> PRIMEM["Greenwich",0],<br> UNIT["degree",0.0174532925199433],<br> AUTHORITY["EPSG","4326"]]<br>Origin = (-54.040095691152260,67.573648952718571)<br>Pixel Size = (0.000424686603675,-0.000424686603675)<br>Metadata:<br> AREA_OR_POINT=Area<br>Image Structure Metadata:<br> INTERLEAVE=BAND<br>Corner Coordinates:<br>Upper Left ( -54.0400957, 67.5736490) ( 54d 2'24.34"W, 67d34'25.14"N)<br>Lower Left ( -54.0400957, 63.4053499) ( 54d 2'24.34"W, 63d24'19.26"N)<br>Upper Right ( -47.7857361, 67.5736490) ( 47d47' 8.65"W, 67d34'25.14"N)<br>Lower Right ( -47.7857361, 63.4053499) ( 47d47' 8.65"W, 63d24'19.26"N)<br>Center ( -50.9129159, 65.4894994) ( 50d54'46.50"W, 65d29'22.20"N)<br>Band 1 Block=14727x1 Type=Int16, ColorInterp=Gray<br><br></font><br></div>Geoid raster:<br><font size="1">Driver: GTX/NOAA Vertical Datum .GTX<br>Files: C:/TEMP/gr20006g06.gtx<br> C:/TEMP/gr20006g06.gtx.aux.xml<br>Size is 651, 251<br>Coordinate System is:<br>GEOGCS["WGS 84",<br> DATUM["WGS_1984",<br> SPHEROID["WGS 84",6378137,298.257223563,<br> AUTHORITY["EPSG","7030"]],<br> TOWGS84[0,0,0,0,0,0,0],<br> AUTHORITY["EPSG","6326"]],<br> PRIMEM["Greenwich",0,<br> AUTHORITY["EPSG","8901"]],<br> UNIT["degree",0.0174532925199433,<br> AUTHORITY["EPSG","9108"]],<br> AUTHORITY["EPSG","4326"]]<br>Origin = (-75.000000000000000,84.000000000000000)<br>Pixel Size = (0.100000000000000,-0.100000000000000)<br>Metadata:<br> AREA_OR_POINT=Point<br>Corner Coordinates:<br>Upper Left ( -75.0000000, 84.0000000) ( 75d 0' 0.00"W, 84d 0' 0.00"N)<br>Lower Left ( -75.0000000, 58.9000000) ( 75d 0' 0.00"W, 58d54' 0.00"N)<br>Upper Right ( -9.9000000, 84.0000000) ( 9d54' 0.00"W, 84d 0' 0.00"N)<br>Lower Right ( -9.9000000, 58.9000000) ( 9d54' 0.00"W, 58d54' 0.00"N)<br>Center ( -42.4500000, 71.4500000) ( 42d27' 0.00"W, 71d27' 0.00"N)<br>Band 1 Block=651x1 Type=Float32, ColorInterp=Undefined<br> NoData Value=9999<br><br></font></div><font size="1"><br><br></font></div><font size="1"><br></font><div><div><div><br clear="all"><div><div><div><div><div><br>-- <br><div class="gmail_signature">Karl Brix Zinglersen<br></div>
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