[gdal-dev] Support for measures

[Even Rouault]

Le mercredi 27 janvier 2016 14:01:42, Ari Jolma a écrit :
> 27.01.2016, 14:34, Ari Jolma kirjoitti:
> > 27.01.2016, 13:27, Even Rouault kirjoitti:
> >> Le mercredi 27 janvier 2016 11:55:01, Ari Jolma a écrit :
> >>> Folks,
> >>> 
> >>> I'd like to try to implement the XYZM support since I have some free
> >>> time.
> >>> 
> >>> Before making a RFC, there are some thoughts/questions/ideas:
> >>> 
> >>> * I made a fork for this work at https://github.com/ajolma/GDAL-XYZM so
> >>> I can more easily use travis.
> >>> 
> >>> * I think this is mainly changes in the geometry API and generic
> >>> methods.
> >>> 
> >>> Are there other drivers than shape, which are affected?
> >> 
> >> On top of my head: PostGIS, FileGDB, OpenFileGDB, GeoPackage,
> >> Spatialite.
> >> Probably other RDMBs too (Oracle, MSSQL, ... ?)
> > 
> > I'm not so sure that it is so many. For example PostGIS driver is
> > mostly moving WKB back and forth.
> 
> Well, it seems that they are affected. There is for example the
> setCoordinateDimension() method, which is called by many drivers and
> once measures are supported it becomes ambiguous since coordinate
> dimension is 3 for both XYM and XYZ.

I think we should perhaps keep setCoordinateDimension() with the current 
semantics for legacy reasons but not accept using 3 for XYM or extending it to 
4 for XYZM

The OGRGeometry class could have for example a setCoordinateInterpretation() 
with an enum XY, XYZ, XYM and XYZM. And a similar member variable to store it.

... or, as currently getGeometryType() dynamically builds the geometry type, 
perhaps have instead a wkbGeometryType member in OGRGeometry itself.

And have a setGeometryType() to modify it, with restrictions on which kind of 
geometry type changes are allowed. You can't  do 
point.SetGeometryType(wkbLineString) )

Actually instead of setGeometryType() , the way QGIS has done with its 
QgsAbstractGeometryV2 class, ie with explicit addZValues( double zInitValue ), 
addZValues( double zInitValue ), dropZValues(), dropMValues() could be a good 
inspiration.

> 
> Ari
> 
> > Anyway, I'll look into the geometry API first.
> > 
> > Ari

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