Hi Felix, Appreciate your alternative solution. I could make some degree of performance improvement.
Thanks a lot for your help, mate. Prem On Fri, 31 Dec 2021 at 7:15 PM, flatoram <felix.v...@gmail.com> wrote: > Hi Prem, > > I experienced those performance issues too. > When i process a lot of routing operations between points I will define an > routing area first on the source network layer (e.g. osm_lines). > I create a tempory layer sometimes in this way with pyqgis: > > # define bounding box and make it a big larger (just an example) > rectangle = QgsRectangle(point_0, point_1) > rectangle = rectangle.scaled(2) # depends on your use case > > # build request > request = QgsFeatureRequest().setFilterRect(rectangle) > # request = request.setNoAttributes() # when you do not need any > attributes > # request = request.setSubsetOfAttributes(["speed"], layer.fields()) # > use only some fields > # add conditions to request to use only features you need, e.g. ignore > specific street types > new_layer = layer.materialize(request) # create a memory copy of source > layer > > In my use cases the new_layer is definitive smaller and more perfomant > than the main layer for those operations. Use the new layer for routing. > But maybe you have not the full available path in your new layer, when your > bbox was to small. > > An other possibility for path finding is QgsTracer class, but it is > different to classic dijsktra/shortestpath when dealing with vertices or > line intersections > > # use qgis tracer, but it is a bit different from classic dijkstra > tracer = QgsTracer() > tracer.setLayers([network_layer]) > # maybe you have to define the destinationCrs > poly_line = tracer.findShortestPath(start_point, end_point)[0] > > > Depends on the use cases I saved a lot of calculation time. > > - Felix > > Am Do., 30. Dez. 2021 um 21:01 Uhr schrieb < > qgis-developer-requ...@lists.osgeo.org>: > >> Send QGIS-Developer mailing list submissions to >> qgis-developer@lists.osgeo.org >> >> To subscribe or unsubscribe via the World Wide Web, visit >> https://lists.osgeo.org/mailman/listinfo/qgis-developer >> or, via email, send a message with subject or body 'help' to >> qgis-developer-requ...@lists.osgeo.org >> >> You can reach the person managing the list at >> qgis-developer-ow...@lists.osgeo.org >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of QGIS-Developer digest..." >> >> >> Today's Topics: >> >> 1. Reusing network graph (Prem Kumar) >> >> >> ---------------------------------------------------------------------- >> >> Message: 1 >> Date: Thu, 30 Dec 2021 19:16:41 +0530 >> From: Prem Kumar <prem.net...@gmail.com> >> To: qgis-developer <qgis-developer@lists.osgeo.org> >> Subject: [QGIS-Developer] Reusing network graph >> Message-ID: >> <CAP2_p600CpiF= >> ejfrsckby7yb1six4vw7fawbcksrrotb9c...@mail.gmail.com> >> Content-Type: text/plain; charset="utf-8" >> >> Hi Team, >> >> I have been trying to get the shortest path for a lot of pairs of start >> and >> end points for a given road layer. Although I'm able to achieve this by >> creating the *QgsVectorLayerDirector *and Graph object for every pair of >> start and end points. >> >> However, I could not reuse the graph object or director object for all the >> pairs of start and end points, eventually the code is as slow as executing >> the* 'native:shortestpathpointtopoint'* processing tool >> programmatically for each pair of start and end points. >> >> Essentially, I'm trying to improve the performance by reusing the graph >> objects. Can someone help me whether there is a possibility to reuse the >> graph object for large sets of pairs? Here is the code snippet I have >> used. >> >> vectorLayer = >> QgsVectorLayer('testdata/network.gpkg|layername=network_lines', >> 'lines')director = QgsVectorLayerDirector(vectorLayer, -1, '', '', '', >> QgsVectorLayerDirector.DirectionBoth)strategy = >> QgsNetworkDistanceStrategy()director.addStrategy(strategy)builder = >> QgsGraphBuilder(vectorLayer.sourceCrs())startPoint = >> QgsPointXY(1179661.925139,5419188.074362)endPoint = >> QgsPointXY(1180942.970617,5420040.097560)tiedPoints = >> director.makeGraph(builder, [startPoint, endPoint])tStart, tStop = >> tiedPointsgraph = builder.graph()idxStart = >> graph.findVertex(tStart)idxEnd = graph.findVertex(tStop)(tree, costs) >> = QgsGraphAnalyzer.dijkstra(graph, idxStart, 0) >> >> -Prem >> -------------- next part -------------- >> An HTML attachment was scrubbed... >> URL: < >> http://lists.osgeo.org/pipermail/qgis-developer/attachments/20211230/acf709c0/attachment-0001.html >> > >> >> ------------------------------ >> >> Subject: Digest Footer >> >> _______________________________________________ >> QGIS-Developer mailing list >> QGIS-Developer@lists.osgeo.org >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer >> >> >> ------------------------------ >> >> End of QGIS-Developer Digest, Vol 194, Issue 18 >> *********************************************** >> >
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