[gdal-dev] GetGeomType() for a MapInfo TAB using OGR MapInfo File driver

[Max Demars]

Hi Even,

Thank you for your reply, that explains a lot. I still wonder why there is
not a possibility to return wkbPolygon like below:

           if( numPoints > 0 && numLines == 0 && numRegions == 0 )
               m_poDefn->SetGeomType( wkbPoint );
           else if( numPoints == 0 && numLines > 0 && numRegions == 0 )
               m_poDefn->SetGeomType( wkbLineString );
+++     else if ( numPoints == 0 && numLines == 0 && numRegions > 0 )
+++         m_poDefn->SetGeomType( wkbPolygon );
           else
               /* we leave it unknown indicating a mixture */;

Maybe there is also a way to check if the layer is made of multi geometries
of one type (no mixture)... It looks to me that the mitab_
tabfile.cpp module could be improved that way. What do you think?

-Max Demars


On Thu, Apr 24, 2014 at 2:23 PM, Even Rouault
<even.rouault at mines-paris.org>wrote:

> Le jeudi 24 avril 2014 19:47:36, Max Demars a écrit :
> > Hi!
> >
> > I am using the OGR MapInfo File driver to read a MapInfo TAB file.
> However,
> > the function
> > GetGeomType()<
> http://gdal.org/python/osgeo.ogr.Layer-class.html#GetGeomTyp
> > e>returns 0 which means point
> > geometry, even if the features in the TAB are only multi-polygons.
>
> No, see ogr_core.h :
>
>     wkbUnknown = 0,         /**< unknown type, non-standard */
>
> >
> > Is it because MapInfo TAB can store many different GeomTypes in the same
> > file?
>
> The MapInfo TAB file will return wkbPoint, wkbLineString or wkbUnknown. The
> later being for polygons/multipolygons, or mix or geometry types.
>
> Source is ogr/ogrsf_frmts/mitab/mitab_tabfile.cpp :
>
>         if( numPoints > 0 && numLines == 0 && numRegions == 0 )
>             m_poDefn->SetGeomType( wkbPoint );
>         else if( numPoints == 0 && numLines > 0 && numRegions == 0 )
>             m_poDefn->SetGeomType( wkbLineString );
>         else
>             /* we leave it unknown indicating a mixture */;
>
>
> >
> > If I take for granted that only one geometry type would always be founded
> > in the TAB, how could I retrieve it?
> >
> >         driver = ogr.GetDriverByName("MapInfo File")
> >         datasource = driver.Open(os.path.join(dirname,shapefileName))
> >         layer = datasource.GetLayer(0)
> >         geometryType = layer.GetGeomType()
> >
> >         >>>geometryType
> >         >>>0
> >
> > Even when looping over features in layer and retrieving geometry type
> using
> > GetDefnRef()<
> http://gdal.org/python/osgeo.ogr.Feature-class.html#GetGeometr
> > yRef>.GetGeomType() the result is always 0 even for multi-polygon
> features.
>
> You should call
>         g = feat.GetGeometryRef()
>         g.GetType()
> to retrieve the geometry type of an individual feature, and that cannot be
> 0=wkbUnknown
>
> layer.GetGeomType(), feat.GetDefnRef().GetGeomType() or
> layer.GetLayerDefn().GetGeomType() are all alias, that will return the
> declared layer geometry type, but not the geometry type of an actual
> feature.
>
> Even
>
> --
> Geospatial professional services
> http://even.rouault.free.fr/services.html
>



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