Hi,
I spent a bit of time learning about vertical datum shifts when performing RPC coordinate transformations using a DEM this week, and I was curious about how the egm96_15.gtx file is interpolated. I was able to find in gdal_rpc.cpp that the required vdatum shift is calculated using an OGR Coordinate Transformation between the DEM spatial reference and a wgs84 ellipsoid spatial reference, but I’m not familiar enough with OGR/PROJ to understand exactly how the gtx file is sampled. Would anyone be able to shed a bit of light on this or point me in the right direction? Cheers, Sebastien
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