Thanks Even. So this means I need to write my own application using the Union() from GEOS and I cannot use it on the command line using OGR VRT? That is OK, I can do that. Using existing utilities on the command line seemed easier ;)
Thanks, Paul 2012/12/17 Even Rouault <even.roua...@mines-paris.org> > Selon Paul Meems <bontepaar...@gmail.com>: > > > Hi all, > > > > How can I union several shapefiles into one using ogr? > > I tried using the OGR Virtual Format and created a XML file similar to > this: > > > > <OGRVRTDataSource> > > <OGRVRTUnionLayer name="unionLayer"> > > <OGRVRTLayer name="source1"> > > <SrcDataSource>source1.shp</SrcDataSource> > > </OGRVRTLayer> > > <OGRVRTLayer name="source2"> > > <SrcDataSource>source2.shp</SrcDataSource> > > </OGRVRTLayer> > > </OGRVRTUnionLayer> > > </OGRVRTDataSource> > > > > My next step was to call ogr2ogr to created the new file. > > The above XML merges all shapes instead of performing an union. > > This depends on how you define union. In the OGR VRT, the UNION is similar > to > the SQL UNION keyword, that is to say that the features of source2 will be > appended after the features of source1 > > > How can I do a proper union using ogr? > > If you rather need a geometrical union ( ST_Union() ), then you can have a > look > at Spatialite (through SQL SQLite dialect for example : > http://www.gdal.org/ogr/ogr_sql_sqlite.html ), or use the new OGR layer > algebra > operations (see > http://www.gdal.org/ogr/ogr__api_8h.html#ac8edb8696c2b046370e29efdd73787f7) > > > > > Thanks, > > > > Paul > > > > >
_______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev