[gdal-dev] Custom vertical transformations

[Kristian Evers]

Thanks for your insights, Even! I had a feeling I was pushing the boundaries here, good to get that confirmed.

The idea of using -s_srs and a correction grid is intriguing. I assume this way will be easier to implement as well since I don't have to worry as much about the CRS and extent of my correction grid as when using gdal_calc. The correction grids I already have are in EPSG:4326 and I assume GDAL is clever enough to handle that or at least pass the responsibility over to PROJ. I'll try a few things and report back how it goes. 

I'll make sure to add a ticket for extending the scope of gdalwarp to the 3D-space.

/Kristian

> -----Original Message-----
> From: Even Rouault <even.rouault at spatialys.com>
> Sent: 20. august 2021 17:30
> To: Kristian Evers <kreve at sdfe.dk>; gdal-dev at lists.osgeo.org
> Subject: Re: [gdal-dev] Custom vertical transformations
> 
> 
> > 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.
> 
> --
> 
> http://www.spatialys.com
> My software is free, but my time generally not.