Fix rare 'waypoints are not included in points' error occurring for edge-based CH alternatives#3139
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Fix rare 'waypoints are not included in points' error occurring for edge-based CH alternatives#3139
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easbar
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Mar 9, 2025
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| @RepeatedTest(value = 1000) | ||
| void testForErrors() { | ||
| // error analysis: | ||
| // * suvPath is found, but uvtPath isn't! | ||
| // * suvPath is some kind of loop leading back close to the start (but not the virtual start node) | ||
| // * the resulting alternative has lower weight than the best path! | ||
| // * the resulting alternative does not even connect the start and target nodes | ||
| long seed = System.nanoTime(); | ||
| System.out.println(seed); | ||
| Random rnd = new Random(seed); | ||
| final BaseGraph graph = new BaseGraph.Builder(em).withTurnCosts(true).create(); | ||
| GHUtility.buildRandomGraph(graph, rnd, 10, 2.0, false, speedEnc, 60.0, 0.5, 0); | ||
| GHUtility.addRandomTurnCosts(graph, seed, null, turnCostEnc, 1, graph.getTurnCostStorage()); | ||
| // GHUtility.printGraphForUnitTest(graph, speedEnc); | ||
| graph.freeze(); | ||
| RoutingCHGraph routingCHGraph = prepareCH(graph); |
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I used this code to produce a simple situation where the error occurs. Just in case we run into a similar problem again.
This was referenced Mar 9, 2025
michaz
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Mar 11, 2025
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michaz
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Super, danke!
Ich glaube, ich vergesse immer, dass es "nicht gefundene Pfade" gibt, die man dann aber trotzdem wie Pfade verwenden kann.
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This bug in
AlternativeRouteEdgeCHwas introduced in #2101: If there is a turn restriction at the node where we 'glue together' the s->v and v->t paths the uvt-path might be empty/not found. This can cause alternative routes that end at node v and thus do not even reach the target node t. Sometimes they also have a lower weight than the best path. Paths that do not end at the target node cause an error inPathMergerreading:Whether the error occurs or not strongly depends on the set of nodes where the forward/backward SPTs overlap which in turn strongly depends on the exact structure of the CH. Therefore the error often cannot be reproduced on a smaller map extract.
The fix is quite simple: We just need to filter out these alternative path candidates.
Related: #2850