How to insert a Path in between an existing Path - graphhopper

Question

I am working on an implementation to generate alternate Paths using via node method.
While checking for local optimality I do the following
forwardEdge = bestWeightMapFrom.get(viaNode);
reverseEdge = bestWeightMapTo.get(viaNode);
double unpackedUntilDistance = 0;
while(forwardEdge.edge != -1) {
double parentDist = forwardEdge.parent != null ? forwardEdge.parent.distance : 0;
double dist = forwardEdge.distance - parentDist;
if(unpackedUntilDistance + dist >= T_THRESHOLD) {
EdgeSkipIterState edgeState = (EdgeSkipIterState) graph.getEdgeProps(forwardEdge.edge, forwardEdge.adjNode);
unpackStack.add(new EdgePair(edgeState, false));
sV = forwardEdge.adjNode;
forwardEdge = forwardEdge.parent;
break;
}
else {
unpackedUntilDistance += dist;
forwardEdge = forwardEdge.parent;
sV = forwardEdge.adjNode;
}
}
int oldSV = forwardEdge.adjNode;
EdgeEntry oldForwardEdge = forwardEdge;
I unpack the edge in the stack to further narrow down sV.
I get vT and oldVt in a similar fashion by traversing reverseEdge.
if I determine that the path from sV and vT is <= length of unpacked edges I accept this via node and construct the alternatePath as follows.
PathBidirRef p = (PathBidirRef) algo.calcPath(oldSV, oldVT);
Path4CHAlt p1 = new Path4CHAlt(graph, flagEncoder);
p1.setSwitchToFrom(false);
p1.setEdgeEntry(oldForwardEdge);
p1.segmentEdgeEntry = p.edgeEntry;
double weight = oldForwardEdge.weight + oldReverseEdge.weight + p.edgeEntry.weight + p.edgeTo.weight;
p1.setWeight(weight);
p1.edgeTo = oldReverseEdge;
p1.segmentEdgeTo = p.edgeTo;
Path p2 = p1.extract();
Path4CHAlt is
public class Path4CHAlt extends Path4CH {
private boolean switchWrapper = false;
public EdgeEntry segmentEdgeTo;
public EdgeEntry segmentEdgeEntry;
public Path4CHAlt( Graph g, FlagEncoder encoder )
{
super(g, encoder);
}
public Path4CHAlt setSwitchToFrom( boolean b )
{
switchWrapper = b;
return this;
}
#Override
public Path extract()
{
System.out.println("Path4CHAlt extract");
if (edgeEntry == null || edgeTo == null || segmentEdgeEntry == null || segmentEdgeTo == null)
return this;
if (switchWrapper)
{
EdgeEntry ee = edgeEntry;
edgeEntry = edgeTo;
edgeTo = ee;
ee = segmentEdgeEntry;
segmentEdgeEntry = segmentEdgeTo;
segmentEdgeTo = ee;
}
EdgeEntry currEdge = segmentEdgeEntry;
while (EdgeIterator.Edge.isValid(currEdge.edge))
{
processEdge(currEdge.edge, currEdge.adjNode);
currEdge = currEdge.parent;
}
currEdge.parent = edgeEntry;
currEdge = edgeEntry;
while (EdgeIterator.Edge.isValid(currEdge.edge))
{
processEdge(currEdge.edge, currEdge.adjNode);
currEdge = currEdge.parent;
}
setFromNode(currEdge.adjNode);
reverseOrder();
currEdge = segmentEdgeTo;
int tmpEdge = currEdge.edge;
while (EdgeIterator.Edge.isValid(tmpEdge))
{
currEdge = currEdge.parent;
processEdge(tmpEdge, currEdge.adjNode);
tmpEdge = currEdge.edge;
}
currEdge.parent = edgeTo;
currEdge = edgeTo;
tmpEdge = currEdge.edge;
while (EdgeIterator.Edge.isValid(tmpEdge))
{
currEdge = currEdge.parent;
processEdge(tmpEdge, currEdge.adjNode);
tmpEdge = currEdge.edge;
}
setEndNode(currEdge.adjNode);
return setFound(true);
}
}
This is not working all the time. I get exceptions in Path4CH
java.lang.NullPointerException
at com.graphhopper.routing.ch.Path4CH.expandEdge(Path4CH.java:62)
at com.graphhopper.routing.ch.Path4CH.processEdge(Path4CH.java:56)
at com.graphhopper.routing.PathBidirRef.extract(PathBidirRef.java:95)
at com.graphhopper.routing.DijkstraBidirectionRef.extractPath(DijkstraBidirectionRef.java:99)
at com.graphhopper.routing.AbstractBidirAlgo.runAlgo(AbstractBidirAlgo.java:74)
at com.graphhopper.routing.AbstractBidirAlgo.calcPath(AbstractBidirAlgo.java:60)
In Path
java.lang.IllegalStateException: Edge 1506012 was empty when requested with node 1289685, array index:0, edges:318
at com.graphhopper.routing.Path.forEveryEdge(Path.java:253)
at com.graphhopper.routing.Path.calcInstructions(Path.java:349)
I dont know what I am doing wrong. I could really use some help with this.
Thanks.

Answer 1

I solved this issue.
Inside DijkstraBidirectionRef.calcPath I was trying to calculate shortest path from an arbitrary node to source node and vertex node.
The error used to occur because the original call to calcPath was operating on QueryGraph and inside I was creating a new Object of DijkstraBidirectionRef using LevelGraphStorage.
This was a problem because QueryGraph may create virtual nodes and edges for source and target nodes. Call to calcPath(node, virtualNode) operating on LevelGraphStorage would throw an exception.
The fix was to call algo.setGraph(queryGraph) after creating DijkstraBidirectionRef.