Class IncrementalDelaunayTriangulator

1	/*
2	* Copyright (c) 2016 Vivid Solutions.
3	*
4	* All rights reserved. This program and the accompanying materials
5	* are made available under the terms of the Eclipse Public License 2.0
6	* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
7	* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
8	* and the Eclipse Distribution License is available at
9	*
10	* http://www.eclipse.org/org/documents/edl-v10.php.
11	*/
12
13	package org.locationtech.jts.triangulate;
14
15	import java.util.Collection;
16	import java.util.Iterator;
17
18	import org.locationtech.jts.triangulate.quadedge.LocateFailureException;
19	import org.locationtech.jts.triangulate.quadedge.QuadEdge;
20	import org.locationtech.jts.triangulate.quadedge.QuadEdgeSubdivision;
21	import org.locationtech.jts.triangulate.quadedge.Vertex;
22
23
24	/**
25	* Computes a Delaunay Triangulation of a set of {@link Vertex}es, using an
26	* incremental insertion algorithm.
27	*
28	* @author Martin Davis
29	* @version 1.0
30	*/
31	public class IncrementalDelaunayTriangulator
32	{
33	private QuadEdgeSubdivision subdiv;
34	private boolean isUsingTolerance = false;
35
36	/**
37	* Creates a new triangulator using the given {@link QuadEdgeSubdivision}.
38	* The triangulator uses the tolerance of the supplied subdivision.
39	*
40	* @param subdiv
41	* a subdivision in which to build the TIN
42	*/
43	public IncrementalDelaunayTriangulator(QuadEdgeSubdivision subdiv) {
44	this.subdiv = subdiv;
45	isUsingTolerance = subdiv.getTolerance() > 0.0;
46
47	}
48
49	/**
50	* Inserts all sites in a collection. The inserted vertices <b>MUST</b> be
51	* unique up to the provided tolerance value. (i.e. no two vertices should be
52	* closer than the provided tolerance value). They do not have to be rounded
53	* to the tolerance grid, however.
54	*
55	* @param vertices a Collection of Vertex
56	*
57	* @throws LocateFailureException if the location algorithm fails to converge in a reasonable number of iterations
58	*/
59	public void insertSites(Collection vertices) {
60	for (Iterator i = vertices.iterator(); i.hasNext();) {
61	Vertex v = (Vertex) i.next();
62	insertSite(v);
63	}
64	}
65
66	/**
67	* Inserts a new point into a subdivision representing a Delaunay
68	* triangulation, and fixes the affected edges so that the result is still a
69	* Delaunay triangulation.
70	* <p>
71	*
72	* @return a quadedge containing the inserted vertex
73	*/
74	public QuadEdge insertSite(Vertex v) {
75
76	/**
77	* This code is based on Guibas and Stolfi (1985), with minor modifications
78	* and a bug fix from Dani Lischinski (Graphic Gems 1993). (The modification
79	* I believe is the test for the inserted site falling exactly on an
80	* existing edge. Without this test zero-width triangles have been observed
81	* to be created)
82	*/
83	QuadEdge e = subdiv.locate(v);
84
85	if (subdiv.isVertexOfEdge(e, v)) {
86	// point is already in subdivision.
87	return e;
88	}
89	else if (subdiv.isOnEdge(e, v.getCoordinate())) {
90	// the point lies exactly on an edge, so delete the edge
91	// (it will be replaced by a pair of edges which have the point as a vertex)
92	e = e.oPrev();
93	subdiv.delete(e.oNext());
94	}
95
96	/**
97	* Connect the new point to the vertices of the containing triangle
98	* (or quadrilateral, if the new point fell on an existing edge.)
99	*/
100	QuadEdge base = subdiv.makeEdge(e.orig(), v);
101	QuadEdge.splice(base, e);
102	QuadEdge startEdge = base;
103	do {
104	base = subdiv.connect(e, base.sym());
105	e = base.oPrev();
106	} while (e.lNext() != startEdge);
107
108	// Examine suspect edges to ensure that the Delaunay condition
109	// is satisfied.
110	do {
111	QuadEdge t = e.oPrev();
112	if (t.dest().rightOf(e) && v.isInCircle(e.orig(), t.dest(), e.dest())) {
113	QuadEdge.swap(e);
114	e = e.oPrev();
115	} else if (e.oNext() == startEdge) {
116	return base; // no more suspect edges.
117	} else {
118	e = e.oNext().lPrev();
119	}
120	} while (true);
121	}
122
123	}
124