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fix an issue with polyline difference #329

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fix an issue with polyline difference #329

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715048c
Fix getting wrong first edge
stolstov Aug 28, 2026
41acac3
Add also a test case for backwards subtractor
stolstov Aug 31, 2026
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78 changes: 36 additions & 42 deletions src/main/java/com/esri/core/geometry/TopologicalOperations.java
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Original file line number Diff line number Diff line change
Expand Up @@ -545,6 +545,7 @@ int selectVertex_(int cluster, EditShape shape) {
}

private double prevailingDirection_(EditShape shape, int half_edge) {
int current_parentage = getCombinedHalfEdgeParentage_(half_edge);
int cluster = m_topo_graph.getHalfEdgeOrigin(half_edge);
int clusterTo = m_topo_graph.getHalfEdgeTo(half_edge);
int signTotal = 0;
Expand All @@ -555,26 +556,28 @@ private double prevailingDirection_(EditShape shape, int half_edge) {
int path = shape.getPathFromVertex(vertex);
int geometry = shape.getGeometryFromPath(path);
int geomID = m_topo_graph.getGeometryID(geometry);
final boolean goodPar = (current_parentage & geomID) != 0;
int nextVert = shape.getNextVertex(vertex);
int prevVert = shape.getPrevVertex(vertex);

int firstVert = shape.getFirstVertex(path);
if (firstVert == vertex) {// remember the first half edge of the
// path. We use it to produce correct
// startpath for closed polyline loops
if (firstVert == vertex && goodPar) {
// remember the first vertex of the path.
// We use it to produce correct startpath for closed polyline loops
m_from_edge_for_polylines = half_edge;
}

if (nextVert != -1
&& m_topo_graph.getClusterFromVertex(nextVert) == clusterTo) {
signTotal++;
if (isGoodParentage(geomID)) {
if (firstVert == nextVert) {// remember the first vertex of
// the path. We use it to
// produce correct startpath for
// closed polyline loops
m_from_edge_for_polylines = m_topo_graph
.getHalfEdgeNext(half_edge);
if (goodPar) {
if (m_from_edge_for_polylines == -1 && firstVert == nextVert) {
// remember the first vertex of the path.
// We use it to produce correct startpath for closed polyline loops
int next = m_topo_graph.getHalfEdgeNext(half_edge);
if (isGoodParentage(getCombinedHalfEdgeParentage_(next))) {
m_from_edge_for_polylines = next;
}
}

// update the sign
Expand All @@ -583,13 +586,14 @@ private double prevailingDirection_(EditShape shape, int half_edge) {
} else if (prevVert != -1
&& m_topo_graph.getClusterFromVertex(prevVert) == clusterTo) {
signTotal--;
if (isGoodParentage(geomID)) {
if (firstVert == prevVert) {// remember the first vertex of
// the path. We use it to
// produce correct startpath for
// closed polyline loops
m_from_edge_for_polylines = m_topo_graph
.getHalfEdgeNext(half_edge);
if (goodPar) {
if (m_from_edge_for_polylines != -1 && firstVert == prevVert) {
// remember the first vertex of the path.
// We use it to produce correct startpath for closed polyline loops
int next = m_topo_graph.getHalfEdgeNext(half_edge);
if (isGoodParentage(getCombinedHalfEdgeParentage_(next))) {
m_from_edge_for_polylines = next;
}
}

// update the sign
Expand Down Expand Up @@ -657,23 +661,17 @@ private void restorePolylineParts_(int first_edge, int newGeometry,
int halfEdgeTwin = m_topo_graph.getHalfEdgeTwin(half_edge);
m_topo_graph.setHalfEdgeUserIndex(half_edge, visitedEdges, 1);
m_topo_graph.setHalfEdgeUserIndex(halfEdgeTwin, visitedEdges, 1);
double prevailingLength = prevailingDirection_(shape, half_edge);// prevailing
// direction
// is
// used
// to
// figure
// out
// the
// polyline
// direction.
//set by the prevailingDirection_()
m_from_edge_for_polylines = -1;

//prevailing direction is used to figure out the polyline direction.
double prevailingLength = prevailingDirection_(shape, half_edge);
// Prevailing length is the sum of the length of vectors that constitute
// the polyline.
// Vector length is positive, if the halfedge direction coincides with
// the direction of the original geometry
// and negative otherwise.

m_from_edge_for_polylines = -1;
int fromEdge = half_edge;
int toEdge = -1;
boolean b_found_impassable_crossroad = false;
Expand All @@ -689,21 +687,21 @@ private void restorePolylineParts_(int first_edge, int newGeometry,
// there is only a single way to pass through.
//When doing planar_simplify we'll never go through the crossroad.
half_edge = tryMoveThroughCrossroadBackwards_(half_edge);
if (half_edge == -1)
if (half_edge == -1) {
b_found_impassable_crossroad = true;
break;
}
else {
b_found_impassable_crossroad = true;
halfEdgeTwin = m_topo_graph.getHalfEdgeTwin(half_edge);
}
} else {
half_edge = halfEdgePrev;
halfEdgeTwin = halfEdgeTwinNext;
}

if (half_edge == first_edge) {// we are in a loop. No need to search
// for the toEdge. Just remember the
// toEdge and skip the next while
// loop.
if (half_edge == first_edge) {
// we are in a loop. No need to search for the toEdge.
//Just remember the toEdge and skip the next while loop.
toEdge = first_edge;
break;
}
Expand Down Expand Up @@ -763,11 +761,9 @@ private void restorePolylineParts_(int first_edge, int newGeometry,

if (m_from_edge_for_polylines != -1) {
fromEdge = m_from_edge_for_polylines;
//try simply getting prev
toEdge = m_topo_graph
.getHalfEdgePrev(m_from_edge_for_polylines);// try
// simply
// getting
// prev
.getHalfEdgePrev(m_from_edge_for_polylines);
int fromEdgeTwin = m_topo_graph.getHalfEdgeTwin(fromEdge);
int fromEdgeTwinNext = m_topo_graph
.getHalfEdgeNext(fromEdgeTwin);
Expand All @@ -788,10 +784,8 @@ private void restorePolylineParts_(int first_edge, int newGeometry,
int e = toEdge;
toEdge = fromEdge;
fromEdge = e;
toEdge = m_topo_graph.getHalfEdgeTwin(toEdge);// switch to twin so
// that we can use
// next instead of
// Prev
//switch to twin so that we can use next instead of Prev
toEdge = m_topo_graph.getHalfEdgeTwin(toEdge);
assert (isGoodParentage(getCombinedHalfEdgeParentage_(toEdge)));
fromEdge = m_topo_graph.getHalfEdgeTwin(fromEdge);
assert (isGoodParentage(getCombinedHalfEdgeParentage_(fromEdge)));
Expand Down
16 changes: 16 additions & 0 deletions src/test/java/com/esri/core/geometry/TestDifference.java
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Original file line number Diff line number Diff line change
Expand Up @@ -511,6 +511,22 @@ public static void testDifferencePolylineAlongPolygonBoundary() {
assertEquals(GeometryEngine.geometryToJson(null, result), "{\"paths\":[[[0,5],[-2,5]]]}");
}

@Test
public static void testIssue328() {
//https://github.com/Esri/geometry-api-java/issues/328
Geometry g1 = OperatorImportFromWkt.local().execute(0,Geometry.Type.Polyline,"MULTILINESTRING ( ( 117422 -64366,119336 -64652,119218 -65440,114999 -64810,115034 -64578,115117 -64022,117422 -64366),(111611 -62617,111365 -64268,110476 -64135,110722 -62484,110975 -62522,111611 -62617))",null);
Geometry g2 = OperatorImportFromWkt.local().execute(0,Geometry.Type.Polyline,"MULTILINESTRING ( (117422 -64366, 117911 -61089))",null);
Geometry g2Backwards = OperatorImportFromWkt.local().execute(0,Geometry.Type.Polyline,"MULTILINESTRING ( (117911 -61089, 117422 -64366))",null);
Geometry res_geom = OperatorDifference.local().execute(g1, g2,null,null);
Geometry resGeomBackwards = OperatorDifference.local().execute(g1, g2Backwards,null,null);
String str = GeometryEngine.geometryToJson(0, res_geom);
String strBackwards = GeometryEngine.geometryToJson(0, resGeomBackwards);
String expectedResult = "{\"paths\":[[[117422,-64366],[119336,-64652],[119218,-65440],[114999,-64810],[115034,-64578],[115117,-64022],[117422,-64366]],[[111611,-62617],[111365,-64268],[110476,-64135],[110722,-62484],[110975,-62522],[111611,-62617]]]}";
assertEquals(str, expectedResult);
assertEquals(strBackwards, expectedResult);
}


public static Polygon makePolygon1() {
Polygon poly = new Polygon();
poly.startPath(0, 0);
Expand Down