[Qgis-user] Struggling with datum transformations and grid shift files

[Neumann, Andreas]

Hi Marco, 

Thanks - now that I know that I need to enter the SRID with the "EPSG:"
prefix, and that I need to use -1 in the Source Datum transformation I
can confirm that it works. 

It would be great, if somewhere in the metadata it would be visible that
this file is now displayed using the nadgrids/GSB file. Otherwise, I
have just to blindly trust, that QGIS does the right thing - which is a
bit scary. 

Do you think it would be possible to add a note in the metadata or
general section of the layer properties confirming that QGIS is using a
datum transformation to display this file? 

I will make sure that the documentation will be improved regarding the
global settings of the datum transformations. 

Thanks,
Andreas 

On 2016-10-04 13:17, Marco Hugentobler wrote:

> 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
>> 
>> _______________________________________________
>> Qgis-user mailing list
>> Qgis-user at lists.osgeo.org
>> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user
>> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user
> 
> -- 
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Weberstrasse 5, CH-8004 Zürich, Switzerland
> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> 
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user
> Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user

  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20161004/9cb28a7c/attachment.html>