[gdal-dev] Closed polyline from DXF as line or area?

[Even Rouault]

Le lundi 26 janvier 2015 15:18:43, Jukka Rahkonen a écrit :
> Spotted from gis.stackexchange:
> 
> http://gis.stackexchange.com/questions/131765/ogr-dxf-closed-polyline-conve
> rsion
> 
> The DXF driver documentation claims that closed polylines from DXF are
> converted into polygons but that does not seem to happen. By comparing the
> DXF snipped from stackexchange
> 
> ENTITIES
>   0
> LWPOLYLINE
>   5
> 20000
>   8
> 0
> 100
> AcDbEntity
> 100
> AcDbPolyline
>  70
> 1
>  90
> 4
> 
> with a DXF specification
> http://www.autodesk.com/techpubs/autocad/acad2000/dxf/lwpolyline_dxf_06.htm
> I can read that LWPOLYLINE [code 70] is defined with flag 1 [closed]. But
> could someone interpret what does it mean in GIS context? Should a closed
> CAD polyline be translated into LINEARRING or POLYGON in WKT?


Jukka,

It seems the documentation matches the initial implementation but has been 
outdated by later changes. Indeed, ogr/ogrsf_frmts/dxf/ogrdxflayer.cpp contains 
the following (disabled) code :

/* -------------------------------------------------------------------- */
/*      If polyline is closed, convert linestring to a linear ring      */
/*                                                                      */
/*      Actually, on review I'm not convinced this is a good idea.      */
/*      Note that most (all) "filled polygons" are expressed with       */
/*      hatches which are now handled fairly well and they tend to      */
/*      echo linear polylines.                                          */
/* -------------------------------------------------------------------- */
#ifdef notdef
    if(m_bClosed)
    {
        OGRLinearRing *poLR = new OGRLinearRing();
        poLR->addSubLineString( poLS, 0 );
        delete poLS;

        // Wrap as polygon.
        OGRPolygon *poPoly = new OGRPolygon();
        poPoly->addRingDirectly( poLR );

        return poPoly;
    }
#endif

Only HATCH (as well as 3DFACE and SOLID) objects are converted as Polygon.

Even

> 
> -Jukka Rahkonen-
> 
> 
> 
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com