Dear all, I'm using RTree to have FAST possibility to extract all the polygons, which intersect a specified window, overlap this specified window or are completely in this window. Please see the picture at http://home.arcor.de/schwar_s/images/polygons.jpg. The idea is to find all the polygons are in the neighbor hood to the polygon in the center of the window. The polygons in the neighborhood are never diagonal but some of them are vertically oriented, some of them are horizontally oriented.
I could not find any possibilities to find all these polygons by using "just" one SQL query, so that I have to execute 6 different queries. These here: //OVERLAP POLYGONS : horizontal overlap SELECT PolyID, X1, X2, Y1, Y2 FROM LDB_RtreePolygons WHERE PolyID != target.PolygonID AND X1< window.x1 AND X2> window.x2 AND Y1>= window.y1 AND Y2<= window.y2 //OVERLAP POLYGONS : vertical overlap SELECT PolyID, X1, X2, Y1, Y2 FROM LDB_RtreePolygons WHERE PolyID != target.PolygonID AND Y1< window.x1 AND Y2> window.y2 AND X1>= window.x1 AND X2<= window.x2 //POLYGONS INTERSECT top/left corner SELECT PolyID, X1, X2, Y1, Y2 FROM LDB_RtreePolygons WHERE PolyID != target.PolygonID AND X2>= window.x1 AND X2<= window.x2 AND Y1>= window.y1 AND Y1<= window.y2 //POLYGONS INTERSECT top/right corner SELECT PolyID, X1, X2, Y1, Y2 FROM LDB_RtreePolygons WHERE PolyID != target.PolygonID AND X1>= window.x1 AND X1<= window.x2 AND Y1>= window.y1 AND Y1<= window.y2 //POLYGONS INTERSECT bottom/left corner SELECT PolyID, X1, X2, Y1, Y2 FROM LDB_RtreePolygons WHERE PolyID != target.PolygonID AND X2>= window.x1 AND X2<= window.x2 AND Y2>= window.y1 AND Y2<= window.y2 //POLYGONS INTERSECT bottom/right corner SELECT PolyID, X1, X2, Y1, Y2 FROM LDB_RtreePolygons WHERE PolyID != target.PolygonID AND X1>= window.x1 AND X1<= window.x2 AND Y2>= window.y1 AND Y2<= window.y2 My 1st question is: ---------------------- Is this the most effective way to find the neighborhood?. Do I really have to specify these 6 queries? The second question (or problem): ---------------------------------------- As long the database file is located locally (at the same computer on which the program is executed) the performance is OK. If the database is placed on another server (in really fast LAN) the performance goes down dramatically (by factor 20x). Even if I "just" extract all existing polygons (without RTree) from the database and then clarify neighborhood by own simple implementation, the performace such solution (in my LAN) is faster by factor 2 in comparation to the RTree-Concept. Are there some RTree-Caching concepts? Any ideas? Thanks in advance! S -- Psssst! Schon vom neuen GMX MultiMessenger gehört? Der kann`s mit allen: http://www.gmx.net/de/go/multimessenger _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
