Hi Andi

>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.


That should work


to 2. and 3. : In the option dialog, you enter the datum transformation id of the datum transformation(s), not the proj parameter.
So to get from epsg:21781 to epsg:2056 with CHENYX06a.gsb, you enter:

Source crs: EPSG:21781
Destination crs: EPSG:2056,
Source datum transformation: 100001
Destination datum transformation: -1

An easier way to get to these numbers is to check the box 'Ask for datum transformations if no default is defined'. Then add a layer in 21781 to the map and transform it to 2056 on-the-fly. In the dialog asking for the datum transformation, check 'Remember selection'. The entry will then appear in the options dialog.

Regards,
Marco

On 10/04/16 12:58, Neumann, Andreas wrote:

Hi,

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,

Andreas



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--
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentob...@sourcepole.ch http://www.sourcepole.ch

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