org.opensphere.geometry.algorithm.ConcaveHull Maven / Gradle / Ivy
/* This file is based on code copied from project OpenSphere, see the LICENSE file for further information. */
package org.opensphere.geometry.algorithm;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import java.util.Map.Entry;
import java.util.TreeMap;
import org.opensphere.geometry.triangulation.DoubleComparator;
import org.opensphere.geometry.triangulation.model.Edge;
import org.opensphere.geometry.triangulation.model.Triangle;
import org.opensphere.geometry.triangulation.model.Vertex;
import org.locationtech.jts.geom.Coordinate;
import org.locationtech.jts.geom.Geometry;
import org.locationtech.jts.geom.GeometryCollection;
import org.locationtech.jts.geom.GeometryFactory;
import org.locationtech.jts.geom.LineSegment;
import org.locationtech.jts.geom.LineString;
import org.locationtech.jts.geom.LinearRing;
import org.locationtech.jts.geom.Point;
import org.locationtech.jts.geom.Polygon;
import org.locationtech.jts.geom.impl.CoordinateArraySequence;
import org.locationtech.jts.operation.linemerge.LineMerger;
import org.locationtech.jts.triangulate.ConformingDelaunayTriangulationBuilder;
import org.locationtech.jts.triangulate.quadedge.QuadEdge;
import org.locationtech.jts.triangulate.quadedge.QuadEdgeSubdivision;
import org.locationtech.jts.triangulate.quadedge.QuadEdgeTriangle;
import org.locationtech.jts.util.UniqueCoordinateArrayFilter;
/**
* Computes a concave hull of a {@link Geometry} which is
* a concave {@link Geometry} that contains all the points
* in the input {@link Geometry}.
* The concave hull is not be defined as unique; here, it is
* defined according to a threshold which is the maximum length
* of border edges of the concave hull.
*
*
* Uses the Duckham and al. (2008) algorithm defined in the paper
* untitled "Efficient generation of simple polygons for characterizing
* the shape of a set of points in the plane".
*
* @author Eric Grosso
*
*/
public class ConcaveHull {
private GeometryFactory geomFactory;
private GeometryCollection geometries;
private double threshold;
public HashMap segments = new HashMap();
public HashMap edges = new HashMap();
public HashMap triangles = new HashMap();
public TreeMap lengths = new TreeMap();
public HashMap shortLengths = new HashMap();
public HashMap coordinates = new HashMap();
public HashMap vertices = new HashMap();
/**
* Create a new concave hull construction for the input {@link Geometry}.
*
* @param geometry
* @param threshold
*/
public ConcaveHull(Geometry geometry, double threshold) {
this.geometries = transformIntoPointGeometryCollection(geometry);
this.threshold = threshold;
this.geomFactory = geometry.getFactory();
}
/**
* Create a new concave hull construction for the input {@link GeometryCollection}.
*
* @param geometries
* @param threshold
*/
public ConcaveHull(GeometryCollection geometries, double threshold) {
this.geometries = transformIntoPointGeometryCollection(geometries);
this.threshold = threshold;
this.geomFactory = geometries.getFactory();
}
/**
* Transform into GeometryCollection.
*
* @param geom
* input geometry
* @return
* a geometry collection
*/
private static GeometryCollection transformIntoPointGeometryCollection(Geometry geom) {
UniqueCoordinateArrayFilter filter = new UniqueCoordinateArrayFilter();
geom.apply(filter);
Coordinate[] coord = filter.getCoordinates();
Geometry[] geometries = new Geometry[coord.length];
for (int i = 0 ; i < coord.length ; i++) {
Coordinate[] c = new Coordinate[] { coord[i] };
CoordinateArraySequence cs = new CoordinateArraySequence(c);
geometries[i] = new Point(cs, geom.getFactory());
}
return new GeometryCollection(geometries, geom.getFactory());
}
/**
* Transform into GeometryCollection.
*
* @param geom
* input geometry
* @return
* a geometry collection
*/
private static GeometryCollection transformIntoPointGeometryCollection(GeometryCollection gc) {
UniqueCoordinateArrayFilter filter = new UniqueCoordinateArrayFilter();
gc.apply(filter);
Coordinate[] coord = filter.getCoordinates();
Geometry[] geometries = new Geometry[coord.length];
for (int i = 0 ; i < coord.length ; i++) {
Coordinate[] c = new Coordinate[] { coord[i] };
CoordinateArraySequence cs = new CoordinateArraySequence(c);
geometries[i] = new Point(cs, gc.getFactory());
}
return new GeometryCollection(geometries, gc.getFactory());
}
/**
* Returns a {@link Geometry} that represents the concave hull of the input
* geometry according to the threshold.
* The returned geometry contains the minimal number of points needed to
* represent the concave hull.
*
* @return if the concave hull contains 3 or more points, a {@link Polygon};
* 2 points, a {@link LineString};
* 1 point, a {@link Point};
* 0 points, an empty {@link GeometryCollection}.
*/
public Geometry getConcaveHull() {
if (this.geometries.getNumGeometries() == 0) {
return this.geomFactory.createGeometryCollection(null);
}
if (this.geometries.getNumGeometries() == 1) {
return this.geometries.getGeometryN(0);
}
if (this.geometries.getNumGeometries() == 2) {
return this.geomFactory.createLineString(this.geometries.getCoordinates());
}
return concaveHull();
}
/**
* Create the concave hull.
*
* @return
* the concave hull
*/
private Geometry concaveHull() {
// triangulation: create a DelaunayTriangulationBuilder object
ConformingDelaunayTriangulationBuilder cdtb = new ConformingDelaunayTriangulationBuilder();
// add geometry collection
cdtb.setSites(this.geometries);
QuadEdgeSubdivision qes = cdtb.getSubdivision();
Collection quadEdges = qes.getEdges();
List qeTriangles = QuadEdgeTriangle.createOn(qes);
Collection qeVertices =
qes.getVertices(false);
int iV = 0;
for (org.locationtech.jts.triangulate.quadedge.Vertex v : qeVertices) {
this.coordinates.put(v.getCoordinate(), iV);
this.vertices.put(iV, new Vertex(iV, v.getCoordinate()));
iV++;
}
// border
List qeFrameBorder = new ArrayList();
List qeFrame = new ArrayList();
List qeBorder = new ArrayList();
for (QuadEdge qe : quadEdges) {
if (qes.isFrameBorderEdge(qe)) {
qeFrameBorder.add(qe);
}
if (qes.isFrameEdge(qe)) {
qeFrame.add(qe);
}
}
// border
for (int j = 0 ; j < qeFrameBorder.size() ; j++) {
QuadEdge q = qeFrameBorder.get(j);
if (! qeFrame.contains(q)) {
qeBorder.add(q);
}
}
// deletion of exterior edges
for (QuadEdge qe : qeFrame) {
qes.delete(qe);
}
HashMap qeDistances = new HashMap();
for (QuadEdge qe : quadEdges) {
qeDistances.put(qe, qe.toLineSegment().getLength());
}
DoubleComparator dc = new DoubleComparator(qeDistances);
TreeMap qeSorted = new TreeMap(dc);
qeSorted.putAll(qeDistances);
// edges creation
int i = 0;
for (QuadEdge qe : qeSorted.keySet()) {
LineSegment s = qe.toLineSegment();
s.normalize();
Integer idS = this.coordinates.get(s.p0);
Integer idD = this.coordinates.get(s.p1);
Vertex oV = this.vertices.get(idS);
Vertex eV = this.vertices.get(idD);
Edge edge;
if (qeBorder.contains(qe)) {
oV.setBorder(true);
eV.setBorder(true);
edge = new Edge(i, s, oV, eV, true);
if (s.getLength() < this.threshold) {
this.shortLengths.put(i, edge);
} else {
this.lengths.put(i, edge);
}
} else {
edge = new Edge(i, s, oV, eV, false);
}
this.edges.put(i, edge);
this.segments.put(s, i);
i++;
}
// hm of linesegment and hm of edges // with id as key
// hm of triangles using hm of ls and connection with hm of edges
i = 0;
for (QuadEdgeTriangle qet : qeTriangles) {
LineSegment sA = qet.getEdge(0).toLineSegment();
LineSegment sB = qet.getEdge(1).toLineSegment();
LineSegment sC = qet.getEdge(2).toLineSegment();
sA.normalize();
sB.normalize();
sC.normalize();
Edge edgeA = this.edges.get(this.segments.get(sA));
Edge edgeB = this.edges.get(this.segments.get(sB));
Edge edgeC = this.edges.get(this.segments.get(sC));
if (edgeA == null || edgeB == null || edgeC == null)
continue;
Triangle triangle = new Triangle(i, qet.isBorder()?true:false);
triangle.addEdge(edgeA);
triangle.addEdge(edgeB);
triangle.addEdge(edgeC);
edgeA.addTriangle(triangle);
edgeB.addTriangle(triangle);
edgeC.addTriangle(triangle);
this.triangles.put(i, triangle);
i++;
}
// add triangle neighbourood
for (Edge edge : this.edges.values()) {
if (edge.getTriangles().size() > 1) {
Triangle tA = edge.getTriangles().get(0);
Triangle tB = edge.getTriangles().get(1);
tA.addNeighbour(tB);
tB.addNeighbour(tA);
}
}
// concave hull algorithm
int index = 0;
while (index != -1) {
index = -1;
Edge e = null;
// find the max length (smallest id so first entry)
int si = this.lengths.size();
if (si != 0) {
Entry entry = this.lengths.firstEntry();
int ind = entry.getKey();
if (entry.getValue().getGeometry().getLength() > this.threshold) {
index = ind;
e = entry.getValue();
}
}
if (index != -1) {
Triangle triangle = e.getTriangles().get(0);
List neighbours = triangle.getNeighbours();
// irregular triangle test
if (neighbours.size() == 1) {
this.shortLengths.put(e.getId(), e);
this.lengths.remove(e.getId());
} else {
Edge e0 = triangle.getEdges().get(0);
Edge e1 = triangle.getEdges().get(1);
// test if all the vertices are on the border
if (e0.getOV().isBorder() && e0.getEV().isBorder()
&& e1.getOV().isBorder() && e1.getEV().isBorder()) {
this.shortLengths.put(e.getId(), e);
this.lengths.remove(e.getId());
} else {
// management of triangles
if (neighbours.size() < 1) continue; //not sure this is safe
Triangle tA = neighbours.get(0);
Triangle tB = neighbours.get(1);
tA.setBorder(true); // FIXME not necessarily useful
tB.setBorder(true); // FIXME not necessarily useful
this.triangles.remove(triangle.getId());
tA.removeNeighbour(triangle);
tB.removeNeighbour(triangle);
// new edges
List ee = triangle.getEdges();
Edge eA = ee.get(0);
Edge eB = ee.get(1);
Edge eC = ee.get(2);
if (eA.isBorder()) {
this.edges.remove(eA.getId());
eB.setBorder(true);
eB.getOV().setBorder(true);
eB.getEV().setBorder(true);
eC.setBorder(true);
eC.getOV().setBorder(true);
eC.getEV().setBorder(true);
// clean the relationships with the triangle
eB.removeTriangle(triangle);
eC.removeTriangle(triangle);
if (eB.getGeometry().getLength() < this.threshold) {
this.shortLengths.put(eB.getId(), eB);
} else {
this.lengths.put(eB.getId(), eB);
}
if (eC.getGeometry().getLength() < this.threshold) {
this.shortLengths.put(eC.getId(), eC);
} else {
this.lengths.put(eC.getId(), eC);
}
this.lengths.remove(eA.getId());
} else if (eB.isBorder()) {
this.edges.remove(eB.getId());
eA.setBorder(true);
eA.getOV().setBorder(true);
eA.getEV().setBorder(true);
eC.setBorder(true);
eC.getOV().setBorder(true);
eC.getEV().setBorder(true);
// clean the relationships with the triangle
eA.removeTriangle(triangle);
eC.removeTriangle(triangle);
if (eA.getGeometry().getLength() < this.threshold) {
this.shortLengths.put(eA.getId(), eA);
} else {
this.lengths.put(eA.getId(), eA);
}
if (eC.getGeometry().getLength() < this.threshold) {
this.shortLengths.put(eC.getId(), eC);
} else {
this.lengths.put(eC.getId(), eC);
}
this.lengths.remove(eB.getId());
} else {
this.edges.remove(eC.getId());
eA.setBorder(true);
eA.getOV().setBorder(true);
eA.getEV().setBorder(true);
eB.setBorder(true);
eB.getOV().setBorder(true);
eB.getEV().setBorder(true);
// clean the relationships with the triangle
eA.removeTriangle(triangle);
eB.removeTriangle(triangle);
if (eA.getGeometry().getLength() < this.threshold) {
this.shortLengths.put(eA.getId(), eA);
} else {
this.lengths.put(eA.getId(), eA);
}
if (eB.getGeometry().getLength() < this.threshold) {
this.shortLengths.put(eB.getId(), eB);
} else {
this.lengths.put(eB.getId(), eB);
}
this.lengths.remove(eC.getId());
}
}
}
}
}
// concave hull creation
List edges = new ArrayList();
for (Edge e : this.lengths.values()) {
LineString l = e.getGeometry().toGeometry(this.geomFactory);
edges.add(l);
}
for (Edge e : this.shortLengths.values()) {
LineString l = e.getGeometry().toGeometry(this.geomFactory);
edges.add(l);
}
// merge
LineMerger lineMerger = new LineMerger();
lineMerger.add(edges);
LineString merge = (LineString)lineMerger.getMergedLineStrings().iterator().next();
if (merge.isRing()) {
LinearRing lr = new LinearRing(merge.getCoordinateSequence(), this.geomFactory);
Polygon concaveHull = new Polygon(lr, null, this.geomFactory);
return concaveHull;
}
return merge;
}
}