[Gdal-dev] exportToGEOS performance

[Pirmin Kalberer]

Frank,
I tried to write my own WKB based exportToGEOS. The geos::WKBReader exists in 
the CVS version of GEOS only. But my usage of istringstream doesn't work. It 
hangs in geosWkbReader.read. Any ideas?
Pirmin

#ifdef HAVE_GEOS
geos::Geometry *exportToGEOS(OGRGeometry *geom)
{
#if GEOS_VERSION_MAJOR*100+GEOS_VERSION_MINOR*10+GEOS_VERSION_PATCH < 300
  return geom->exportToGEOS();
#else
    GByte       *pabyWKB;
  
    pabyWKB = (GByte *) CPLMalloc(geom->WkbSize());
    geos::WKBReader   geosWkbReader( 
        *OGRGeometryFactory::getGEOSGeometryFactory() );
    if( geom->exportToWkb( wkbNDR, pabyWKB ) != OGRERR_NONE )
        return NULL;

    istringstream oWKB((const char*)pabyWKB, istringstream::in | 
istringstream::binary);
    CPLFree( pabyWKB );

    try 
    { 
        geos::Geometry *geosGeometry = NULL;
        geosGeometry = geosWkbReader.read( oWKB );
        return geosGeometry;
    }
    catch( geos::GEOSException *e )
    {
        CPLError( CE_Failure, CPLE_AppDefined,
                  "GEOSException: %s", 
                  e->toString().c_str() );

        delete e;
        return NULL;
    }
#endif
}
#endif /* HAVE_GEOS */


Am Donnerstag, 6. Oktober 2005 18.17 schrieb Frank Warmerdam:
> On 10/6/05, Pirmin Kalberer <sp_ml at sourcepole.com> wrote:
> > Hi,
> >
> > I'm using the GEOS polygonizer for the OGR Interlis driver. But the
> > polygonization is quite slow because of the exportToGEOS call. The code
> > looks like this:
> >
> >     geos::Geometry *poThisGeosGeom = poLines->exportToGEOS(); //slow
> >     geos::Polygonizer* polygonizer = new geos::Polygonizer();
> >     polygonizer->add(poThisGeosGeom);
> >     vector<geos::Polygon*> *poOtherGeosGeom = polygonizer->getPolygons();
> >
> > We're talking about exporting 1677 OGRLineString's in about 1'20'' and
> > polygonizing them within a few second.
>
> Pirmin,
>
> I was planning to rewrite exportToGEOS() to translate using WKB
> format instead of WKT which I suspect will be significantly faster.
> This will be part of an upgrade to use the GEOS C API in time for
> the next release.  In the meantime, you might want to try modifying
> your local copy to go via WKB instead of WKT.  I think when I
> first looked at GEOS only the WKT conversion was supported.
>
> Best regards,
> --
> ---------------------------------------+-----------------------------------
>--- I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com light and sound - activate the windows |
> http://pobox.com/~warmerdam and watch the world go round - Rush    |
> Geospatial Programmer for Rent

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