[gdal-dev] RFC 61: Call for vote on adoption

[Pirmin Kalberer]

Hi,

Am Montag, 8. Februar 2016, 10.04:55 schrieb Even Rouault:
> Le lundi 08 février 2016 08:17:28, vous avez écrit :
> > 06.02.2016, 18:00, Sean Gillies kirjoitti:
> > > Can you explain more in detail about the backwards incompatibilities
> > > and how to soften them? What's going to break and what are the
> > > specific options?
> > 
> > Hi Sean,
> > 
> > In the C++ and C API there are no backwards incompatibilities but the
> > get/setCoordinateDimension() methods become deprecated since XYM and XYZ
> > have the same dimension.  Is3D(), IsMeasured(), set3D(), and
> > setMeasured() should be used instead.
> > 
> > I don't know about the other drivers but Shapefile driver currently
> > reads XYM geometries as XYZ and that will be changed so that XYM are
> > read as XYM. I think that is the only incompatibility. A new open option
> > MEASURE_AS_Z=YES/NO (or something) can be defined for backwards
> > compatibility.
> 
> I don't think there's a strong need for such an option without confirmation
> from users. The XYM support as XYZ was really a hack (people had no way to
> know if the XYZ was XYM or XYZ, unless they read the .shp/.shx themselves).
> And it is not clear how that would work in update scenarios (currently the
> M/Z is discarded on update :  https://trac.osgeo.org/gdal/ticket/6331 )
> 
> Pirmin: as I see from https://trac.osgeo.org/gdal/ticket/2374 you were the
> one to contribute the patch, what is your opinion on this ?

Completeley forgot that... We had a customer request for accessing M values in 
Shapefiles from QGIS and the result was this hacky solution.
In my opinion we can live without a compatibilty switch to this intermediate 
solution when a proper API for XYZM is provided. It will be easy to adapt that 
in a coming version of QGIS (update would be needed also for setting the 
compatibility switch) and in the meantime they have to stay on their GDAL 
version (what they usually do anyway). So an incompatibility warning in the 
release notes would be enough for me.

Regards
Pirmin

-- 
Pirmin Kalberer
Sourcepole  -  Linux & Open Source Solutions
http://www.sourcepole.com