[gdal-dev] Custom vertical transformations

[Even Rouault]

> Regarding your immediate issue, the workaround I see would be that you 
> use PROJ to create a regular grid that contains the vertical 
> correction, use gdalwarp to transform it to the exact extent and 
> resolution of the result of your 2D-only gdalwarp, and finally use 
> gdal_calc to sum the two.
>
Well, if you actually create a vertical correction only grid, then you 
could just use  -s_srs "+proj=longlat +ellps=... 
+geoidgrids=your_tif_or_gtx"  (or maybe as output, or fix the sign of 
the correction in the grid), since the workaround I give above is what 
gdalwarp would do. But of course none of this will solve the 
time-dependent aspect you need.

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