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Isochrone calculation with GraphHopper
/* This program is free software: you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License
as published by the Free Software Foundation, either version 3 of
the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see seedEdges) {
Set processed = new HashSet<>();
List rings = new ArrayList<>();
for (ReadableQuadEdge f : seedEdges) {
ReadableQuadEdge e = f.getPrimary();
if (processed.contains(e))
continue;
processed.add(e);
int cut = cut(e.orig().getZ(), e.dest().getZ(), z0);
if (cut == 0) {
continue; // While, next edge
}
List polyPoints = new ArrayList<>();
boolean ccw = cut > 0;
while (true) {
// Add a point to polyline
Coordinate cC;
if (isFrameVertex(e.orig())) {
cC = moveEpsilonTowards(e.dest().getCoordinate(), e.orig().getCoordinate());
} else if (isFrameVertex(e.dest())) {
cC = moveEpsilonTowards(e.orig().getCoordinate(), e.dest().getCoordinate());
} else {
cC = e.orig().midPoint(e.dest()).getCoordinate();
}
polyPoints.add(new Coordinate(cC.x, cC.y)); // Strip z coordinate
processed.add(e);
ReadableQuadEdge E1 = ccw ? e.oNext().getPrimary() : e.oPrev().getPrimary();
ReadableQuadEdge E2 = ccw ? e.dPrev().getPrimary() : e.dNext().getPrimary();
int cut1 = E1 == null ? 0 : cut(E1.orig().getZ(), E1.dest().getZ(), z0);
int cut2 = E2 == null ? 0 : cut(E2.orig().getZ(), E2.dest().getZ(), z0);
boolean ok1 = cut1 != 0 && !processed.contains(E1);
boolean ok2 = cut2 != 0 && !processed.contains(E2);
if (ok1) {
e = E1;
ccw = cut1 > 0;
} else if (ok2) {
e = E2;
ccw = cut2 > 0;
} else {
// This must be the end of the polyline...
break;
}
}
// Close the polyline
polyPoints.add(polyPoints.get(0));
if (polyPoints.size() >= 4) {
LinearRing ring = geometryFactory.createLinearRing(polyPoints
.toArray(new Coordinate[polyPoints.size()]));
rings.add(ring);
}
}
List isolinePolygons = punchHoles(rings);
return geometryFactory.createMultiPolygon(isolinePolygons.toArray(new Polygon[isolinePolygons.size()]));
}
private boolean isFrameVertex(Vertex v) {
return v.getZ() == Double.MAX_VALUE;
}
private Coordinate moveEpsilonTowards(Coordinate coordinate, Coordinate distantFrameCoordinate) {
return new Coordinate(coordinate.x + EPSILON * (distantFrameCoordinate.x - coordinate.x), coordinate.y + EPSILON * (distantFrameCoordinate.y - coordinate.y));
}
private int cut(double za, double zb, double z0) {
if (za <= z0 && zb > z0) return 1;
if (za > z0 && zb <= z0) return -1;
return 0;
}
@SuppressWarnings("unchecked")
private List punchHoles(List rings) {
List shells = new ArrayList<>(rings.size());
List holes = new ArrayList<>(rings.size() / 2);
// 1. Split the polygon list in two: shells and holes (CCW and CW)
for (LinearRing ring : rings) {
if (CGAlgorithms.signedArea(ring.getCoordinateSequence()) > 0.0)
holes.add(ring);
else
shells.add(new PreparedPolygon(geometryFactory.createPolygon(ring)));
}
// 2. Sort the shells based on number of points to optimize step 3.
shells.sort((o1, o2) -> o2.getGeometry().getNumPoints() - o1.getGeometry().getNumPoints());
for (PreparedPolygon shell : shells) {
shell.getGeometry().setUserData(new ArrayList());
}
// 3. For each hole, determine which shell it fits in.
for (LinearRing hole : holes) {
outer: {
// Probably most of the time, the first shell will be the one
for (PreparedPolygon shell : shells) {
if (shell.contains(hole)) {
((List) shell.getGeometry().getUserData()).add(hole);
break outer;
}
}
throw new RuntimeException("Found a hole without a shell.");
}
}
// 4. Build the list of punched polygons
List punched = new ArrayList<>(shells.size());
for (PreparedPolygon shell : shells) {
List shellHoles = ((List) shell.getGeometry().getUserData());
punched.add(geometryFactory.createPolygon((LinearRing) (((Polygon) shell.getGeometry()).getExteriorRing()),
shellHoles.toArray(new LinearRing[shellHoles.size()])));
}
return punched;
}
}