[geos-devel] about OGRGeometry's Union/Intersection/Difference unsuccessfully.

[xhgis]

hello,everyone!
I couldn't succeed to use OGRGeometry's Union/Intersection/Difference function. Union two Geometrys,but get a null value. I couldn't find some errors.
the following code,thanks.

{
OGRRegisterAll();

    OGRDataSource       *poDS;
    poDS = OGRSFDriverRegistrar::Open("f:\\t1.shp", FALSE ); // Only include two polygon features. SRS is null. 
    if( poDS == NULL )
    {
        printf( "Open failed.\n%s" );
        exit( 1 );
    }
    OGRLayer *poLayer;
    poLayer = poDS->GetLayerByName( "t1" );
    
    OGRFeature *poFeature0;
    OGRFeature *poFeature1;
    poLayer->ResetReading();
     poFeature0=poLayer->GetNextFeature();
    poFeature1=poLayer->GetNextFeature();
    
    OGRGeometry *geoS0;
    OGRGeometry *geoS1;
    geoS0=poFeature0->GetGeometryRef();
    geoS1=poFeature1->GetGeometryRef();
    
    OGRPolygon *pgon0=(OGRPolygon*)geoS0;
    OGRPolygon *pgon1=(OGRPolygon*)geoS1;

    OGRGeometry *g2=geoS0->Intersection(geoS1);
//OGRGeometry *g2=geoS0->Union(geoS1);...
//g2 always is null?

 OGRFeature::DestroyFeature( poFeature0 );
    OGRFeature::DestroyFeature( poFeature1 );
OGRDataSource::DestroyDataSource( poDS );
}
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