Some time ago, I wrote a text (in the QGIS portuguese user group blog)
about the use of coordinate transformations and NTv2 grids in QGIS. It's in
portuguese, but maybe google translator can help you get the idea. I hope
2016-10-04 11:58 GMT+01:00 Neumann, Andreas <a.neum...@carto.net>:
> I am struggling in QGIS 2x with datum transformations.
> The manual is not explicit how to handle this correctly.
> Here are the steps I tried:
> 1. As far as I understand, I have to copy the gsb file to the directory
> where proj stores the gsb files, in my case "C:\Program
> Files\OSGeo4W64\share\proj". Alternatively, one could set another folder
> and adjust the PROJ_LIB env variable accordingly.
> 2. In "Settings" --> "Options" --> "CRS" I can define default datum
> transformations. I tried to enter 21781 (Source CRS), 2056 (Destination
> CRS), +nadgrids=CHENYX06a.gsb (Source datum transfomation). Destionation
> datum has been left empty.
> 3. I would expect that whenever this combination 21781 --> 2056 shows up
> that QGIS would ask me to pick one the defaults specified in 2.
> The problem is that 2. does not work. When I close the dialogue and reopen
> it, my modifications are gone ... and I never have the chance to select my
> datum transformation option.
> Can you help me what I am doing things wrong?
> Thank you,
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