[QGIS-Developer] Geoprocessing tools give empty results for data using crs EPSG:7694

[Stéphane Henriod]

Wow this is a hell of a comprehensive answer :)

Thank you very much... My bad, I didn't even think about checking the
validity of the geometries here.  I will correct them and make further tests

Cheers
Stéphane

On 28 Jul 2017 9:39 p.m., "Giovanni Manghi" <giovanni.manghi at gmail.com>
wrote:

> Hi,
>
>
> > Hi all
> >
> > I have made a few tests of GDAL 2.2.0 on Ubuntu 16.04 with QGIS 2.14.14
> and
> > have found out that most geoprocessing tools implying 2 layers (clip,
> > difference, intersection, etc.) wrongly give empty geometries when the
> data
> > is in CRS  EPSG:7694 (*Kyrg06-3*, newly added CRS to GDAL in 2.2.0). Same
> > behavior with QGIS 2.18.11 with GDAL 1.11.3
> >
> > For example, when using the Tool *Vector - Geoprocessing tools -
> Difference*
> > the difference between 2 layers gives an empty geometry. Using the same
> > tool on the same data with the CRS 32643 (*WGS84 UTM43N*) gives correct
> > results.
> >
> > I have communicated on the Ubuntugis mailing list and got the following
> > feedback from Even Rouault:
> >
> > *I've run ogrinfo -al shp > log.txt on your dataset with GDAL 2.2 and
> GDAL
> > 2.1 and get almost the same results. The only difference is that GDAL 2.2
> > now reports the SRS of layers kyrgyzstan_UTM43N and rayons_UTM43N with an
> > explicit EPSG:32643 code, which is an intended change of GDAL 2.2, and I
> > wouldn't think that would cause issues to QGIS. So my feeling is that the
> > issue is more with the processing tool itself, or a subtle issue in the
> > integration of QGIS&GDAL.*
> >
> > Test dataset (in both CRS) here: http://www.henriod.info/share/shp.zip
> >
> > Is it something to be reported as a QGIS bug? Can you reproduce this
> > behavior?
>
>
> I made some test and here following a few notes:
>
>
> 1) the geoprocressing tools in the "vector" menu are the native QGIS
> ones, and I don't thinkthey make use of GDAL/OGR to make the
> operations, on the other hand in the Processing toolbox you find also
> a few ones (I have in mind since a long to add more) really based on
> GDAL/OGR.
>
>
> 2) I noticed that in your layers in EPSG:7694 there are geometries
> errors that are not present in the EPSG:32643, and here lies the
> problem of the wrong results you see, it does not depend on the CRS of
> the inputs.
>
>
> 3) I fixed the inputs geometry errors with my favorite tool, the
> liblwgeom plugin for the Processing toolbox and its "MakeValid" tool
> (equivalent to PostGIS's ST_MakeValid) and after that the operation
> returned the expected results
>
>
> 4) The geoprocessing OGR based tools are more verbose in their log and
> so was easy to spot the geometry error messages
>
>
> 5) the OGR based "clip by vector" tool returned also an output in
> EPSG:7694 while the equivalent QGIS tool returned an output with 4326
> assigned CRS, but if you change it manually the result is there and in
> the right place.
>
>
>
> hope this helps
>
> -- G --
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