[gdal-dev] Problem with Shapefile and CRS 2056/21781

[Stefan Keller]

2016-04-24 17:58 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> I guess we would want to improve the shapefile importer to get the WKT
> definition from the GDAL EPSG DB when a AUTHORITY EPSG node is found. Could you
> create a ticket about that ?

Done: https://trac.osgeo.org/gdal/ticket/6485

:Stefan


2016-04-24 17:58 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> Le dimanche 24 avril 2016 17:46:45, Stefan Keller a écrit :
>> 2016-04-24 17:34 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
>> > Could you post the .prj file ?
>>
>> Bien sur: I posted both CRS.
>> Hope attachments come through.
>
> OK, that explains it.
>
> The .prj file are somewhere between a old-style ESRI WKT and regular OGC WKT,
> in that they have a AUTHORITY EPSG node, but no TOWGS84 node.
> Hence when you do the direct conversion, no datum shift is taken into account.
> When you do the 2-step conversion, in the first step, the GPKG driver has a
> logic to add entries in its gpkg_spatial_ref_sys table based on the source
> SRS. When the source SRS has a EPSG node, the WKT definition is read from the
> GDAL SRS db from the EPSG code (thus ignoring the rest of the WKT), which
> brings back the default TOWGS84. The second ogr2ogr call then applies it when
> reprojecting.
>
> I guess we would want to improve the shapefile importer to get the WKT
> definition from the GDAL EPSG DB when a AUTHORITY EPSG node is found. Could you
> create a ticket about that ?
>
> Even
>
>>
>> :Stefan
>>
>> 2016-04-24 17:34 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
>> > Le dimanche 24 avril 2016 17:29:36, Stefan Keller a écrit :
>> >> Given a Shapefile "swiss_admin_boundaries.shp" in EPSG:2056 (or 21781,
>> >> to be downloaded for free at [1]) I have problems transforming it to
>> >> any other SRS/CRS.
>> >
>> > Could you post the .prj file ?
>> >
>> >> When doing this:
>> >> > ogr2ogr -f "GPKG" swiss_admin_boundaries1.gpkg
>> >> > swiss_admin_boundaries.shp -t_srs EPSG:3857
>> >>
>> >> ... swiss_admin_boundaries2.gpkg have a shift of about 150m.
>> >>
>> >> But when I convert Shapefile first e.g. to GeoPackage, and transform then:
>> >> > ogr2ogr -f "GPKG" tmp.gpkg swiss_admin_boundaries.shp
>> >> > ogr2ogr -f "GPKG" swiss_admin_boundaries2.gpkg tmp.gpkg -t_srs
>> >> > EPSG:3857 del tmp.gpkg
>> >>
>> >> ... swiss_admin_boundaries2.gpkg is correct!
>> >>
>> >> What could be the reason?
>> >>
>> >> :Stefan
>> >>
>> >> [1] https://opendata.swiss/en/dataset/swissboundaries3d-gemeindegrenzen
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