Hi Andreas I did some investigation and found the following answers to your questions:
> Is the id 100001 for the swiss datum transformation stable? > Are those .gsb file names hard coded somewhere? I suppose the id is stable. The id and the .gsb file names seem to be hard coded in the srs.db template. Apparently the id for CHENYX06a.gsb has been defined in commit https://github.com/qgis/QGIS/commit/3465c3eb509b9285f0b7d99129dcbaad84463771 > The table tbl_datum_transformation does not contain any references to the > .gsb files. How does QGIS find those files? QGIS seems to look for the .gsb files in the directory where Proj.4 stores them: /usr/share/proj (I see you figured this out too) Thanks a lot for updating the documentation. Btw. now I guess that it’s possibly not even necessary to run crssync (opposed to what I wrote earlier). Andy Von: Neumann, Andreas [mailto:a.neum...@carto.net] Gesendet: Freitag, 28. Oktober 2016 16:56 An: Schmid Andreas Cc: 'rich...@duif.net'; 'QGIS User List' Betreff: Re: [Qgis-user] QGIS server: configuration of grid shift files for datum conversions I was able to fix the crash by naming the .gsb files EXACTLY like Andy wrote below - my name before was chenys06a.gsb. After I created a symblink to CHENYX06a.gsb the crash was gone. This looks really strange. Are thoses .gsb file names hard coded somewhere? Quite a mystery ... Andreas On 2016-10-28 16:45, Neumann, Andreas wrote: Hi Andy, Thank for these very precise instructions. I was able to do the same on CentOS 7 with only very minor differences (probably because I self-compile QGIS server). Is the id 100001 for the swiss datum transformation stable? I think this information should be added to the QGIS user manual, in the server section. I created a pull request: https://github.com/qgis/QGIS-Documentation/pull/1481 ------- fyi: i get a server crash when I use a request in EPSG:2056, project done in EPSG:21781 - still investigating what the reason is ... Thanks a lot - very useful information! Andreas On 2016-10-24 11:09, Schmid Andreas wrote: Hi, At Kanton Solothurn we had the same requirement. And we did not want to fiddle with the original proj.4 definition files. So we paid Sourcepole for solving this directly in QGIS Server (https://github.com/qgis/QGIS/commit/70863ecaf0ccfcb538e3892af4b528304b21a0a2). This is how it works under Ubuntu: * Place those CHENYX06a.gsb and CHENYX06_etrs.gsb in /usr/share/proj (probably in our case only CHENYX06a.gsb is actually needed) * If QGIS Server was installed before placing the .gsb files, run /usr/lib/qgis/crssync (or run it anyway) * In /etc/apache2/mods-enabled/fcgid.conf place the following additional option: InitialEnv DEFAULT_DATUM_TRANSFORM=EPSG:21781/EPSG:2056/100001/-1;EPSG:2056/EPSG:21781/-1/100001 The meaning of this option is: when your .qgs is in EPSG:21781 and the WMS request is in EPSG:2056, then use datum transformation 100001; when your .qgs is in EPSG:2056 and the WMS request is in EPSG:21781, then use datum transformation 100001 as well, but use it the other way round. The datum transformation code 100001 can be looked up in /usr/share/qgis/resources/srs.db. Look at attribute coord_op_code of table tbl_datum_transform. Regards, Andy -----Ursprüngliche Nachricht----- Von: Qgis-user [mailto:qgis-user-boun...@lists.osgeo.org<mailto:qgis-user-boun...@lists.osgeo.org>] Im Auftrag von Richard Duivenvoorde Gesendet: Montag, 24. Oktober 2016 10:01 An: Neumann, Andreas Cc: QGIS User List Betreff: Re: [Qgis-user] QGIS server: configuration of grid shift files for datum conversions On 2016-10-24 06:23, Neumann, Andreas wrote: Hi, I have to configure QGIS server to properly handle grid shift files. In Switzerland we need to offer "old" and "new" coordinates (different datums) at the same time with our services and the conversion needs to be done with grid shift files or tin based interpolation. I know that I have to copy the CHENYX06a.gsb file to my proj lib, e.g. /usr/local/shar/proj - but how can I make QGIS Server to actually use this file? I assume that I need to copy an additional config file or SRS/grid shift file combinations to QGIS server and/or specify an environment variable - right? Are there any resources explaining how I can configure QGIS server to make use of these grid shift files? Thank you for any pointers! Hi Andreas, funny, in NL we just had a discussion about how to handle different available datum transformation too last week... we also recently got a grid shift file to better handle datum transformation and I found this post of Sourcepole: http://blog.sourcepole.ch/2014/02/18/ntv2-transformations-with-qgis/ Which I think answers your question (at least for the desktop side) But from a mini presentation from somebody from our National Cadastre, I actually draw the conclusion that the way QGIS represents CRS's is too narrow/not complete... Please correct me if I'm wrong, but a lot of 'On The Fly'-reprojections actually need 2(!) proj configurations/steps: - the projection parametes (mostly available in the epsg database) - the datum transformation parameters (these is the 'towsg84...'-part, AND only needed when you do an actual datum transformation, PARTLY available in the epsg database) The last part can either be a list of parameters (to calculate it) OR (as in your case and in the dutch preferred case) a grid shift file (as proj can only handle one of these). SO: for example for certain crs's (in QGIS the dutch one is called epsg:28992) there is actually a SET of combinations available: the projection and 4 or 5 transformations (http://pix.toile-libre.org/upload/original/1477238061.png), QGIS actually picks one (from qgis.db) of these and present them to the user as THE epsg:28992 crs, while in our case this is actually not the best fit, and in your case you actually want to pick two! I understood that in ArcGIS, the user actually every time is presented with a 'pick the right datum transformation' dialog as soon as the data needs a datum transformatio. As a draw back: making it more difficult for new users to pick the right one, BUT on the positive side making it easier to pick the right projection/datumtransformation pair! So what about using both worlds: - in the qgis.db / crs table NOT use the projection-name as crs-identifier (so NOT epsg:28992), BUT the combination of projection AND datumtransformation, so in our case (28992_4833, 28992_15934, or epsg28992_epsg4833, epsg28992_qgis0001 to be able to handle projection/transformation combinations not available in the epsg db) - and instead of current possibility to have a 'check'-box to have the 'select datum transformation' popup we make this available in the 'choose crs'-dialog with a button, and then 'remember' the last used crs's (in which a crs is NOT only the projection anymore but a projection/transformation combi) IF QGIS starts using this combinations AND proj/gdal will ship all gridfiles towgs-paramters etc etc, this will become a better world :-) Does this make sense? Do others get excited from this idea too? Regards, Richard Duivenvoorde ps about providing the gridfiles, I urge our national Kadaster to make it available as treu open geodata, that is without a copyright disclaimer, so it can be picked up by Debian and other distro's. _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org<mailto:Qgis-user@lists.osgeo.org> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user _______________________________________________ Qgis-user mailing list Qgis-user@lists.osgeo.org<mailto:Qgis-user@lists.osgeo.org> List info: http://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: http://lists.osgeo.org/mailman/listinfo/qgis-user
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