[gdal-dev] Interpolation used for egm96_15.gtx when using RPC_DEM_APPLY_VDATUM_SHIFT

[Yann-Sebastien Tremblay-Johnston]

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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