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

[Even Rouault]

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

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