[gdal-dev] Custom vertical transformations

[Kristian Evers]

Very cool, Even! In the end I managed to come up with a solution that uses +geoidgrids
but this will certainly make things easier in the future. Thanks for taking the time to
implement this!

/Kristian

> -----Original Message-----
> From: Even Rouault <even.rouault at spatialys.com>
> Sent: 11. oktober 2021 23:36
> To: Kristian Evers <kreve at sdfe.dk>; gdal-dev at lists.osgeo.org
> Subject: Re: [gdal-dev] Custom vertical transformations
> 
> Kristian,
> 
> https://github.com/OSGeo/gdal/pull/4639 will allow you to use an
> arbitrary pipeline to do a vertical transformation through gdalwarp
> 
> Even
> 
> Le 23/08/2021 à 10:50, Kristian Evers a écrit :
> > 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.
> 
> --
> http://www.spatialys.com
> My software is free, but my time generally not.