Hi On Wed, Jul 27, 2011 at 8:56 PM, maaza mekuria <sail...@yahoo.com> wrote: > I am just wondering if one could use the following in a spatial index created > from the layer provider > > QgsVectorLayer* cvertexLayer = cVertexLayer(txtStream); > QgsVectorDataProvider* cvectorProvider = cvertexLayer->dataProvider(); > bool blnSpatialIdx = cvectorProvider->createSpatialIndex();
createSpatialIndex() method is supported only by memory provider and by OGR provider for shapefiles. With shapefiles it means that a .qix file is created with a quadtree structure. Memory provider builds R-tree (using QgsSpatialIndex class). > After creating the spatial index file how can I access it in code? > can I use it in anyway to perform spatial filters for selection purposes? > > QgsSpatialIndex mSpatialIndex = <dynamic_Cast> cvectorProvider; // may be > cvectorLayer; > > or may be even directly perform this > > QgsSpatialIndex mSpatialIndex = cvectorProvider->createSpatialIndex(); > > // and then do something like this > mSpatialIndex.intersects( rect ); No. You cannot access the provider's spatial index. Some providers do not support spatial indexing, others (optionally) use it, but it is invisible for the client. When you call provider.select( ... ) and specify a rectangle, you will get only features that are inside this rectangle - and if a spatial index is available then it will be used for faster access. > DO I have to create my own in memory spatial index to perform the above > > what do you think? If you build an application where you need to do lots of spatial queries it makes sense to load all the features into a spatial index (QgsSpatialIndex) and do the intersect / nearest neighbor queries using it. Martin _______________________________________________ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
