Class GeometryCombiner

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.geom.util;
14
15	import java.util.ArrayList;
16	import java.util.Collection;
17	import java.util.Iterator;
18	import java.util.List;
19
20	import org.locationtech.jts.geom.Geometry;
21	import org.locationtech.jts.geom.GeometryCollection;
22	import org.locationtech.jts.geom.GeometryFactory;
23	import org.locationtech.jts.geom.Polygonal;
24
25
26	/**
27	* Combines {@link Geometry}s
28	* to produce a {@link GeometryCollection} of the most appropriate type.
29	* Input geometries which are already collections
30	* will have their elements extracted first.
31	* No validation of the result geometry is performed.
32	* (The only case where invalidity is possible is where {@link Polygonal} geometries
33	* are combined and result in a self-intersection).
34	*
35	* @author mbdavis
36	* @see GeometryFactory#buildGeometry
37	*/
38	public class GeometryCombiner
39	{
40	/**
41	* Combines a collection of geometries.
42	*
43	* @param geoms the geometries to combine
44	* @return the combined geometry
45	*/
46	public static Geometry combine(Collection geoms)
47	{
48	GeometryCombiner combiner = new GeometryCombiner(geoms);
49	return combiner.combine();
50	}
51
52	/**
53	* Combines two geometries.
54	*
55	* @param g0 a geometry to combine
56	* @param g1 a geometry to combine
57	* @return the combined geometry
58	*/
59	public static Geometry combine(Geometry g0, Geometry g1)
60	{
61	GeometryCombiner combiner = new GeometryCombiner(createList(g0, g1));
62	return combiner.combine();
63	}
64
65	/**
66	* Combines three geometries.
67	*
68	* @param g0 a geometry to combine
69	* @param g1 a geometry to combine
70	* @param g2 a geometry to combine
71	* @return the combined geometry
72	*/
73	public static Geometry combine(Geometry g0, Geometry g1, Geometry g2)
74	{
75	GeometryCombiner combiner = new GeometryCombiner(createList(g0, g1, g2));
76	return combiner.combine();
77	}
78
79	/**
80	* Creates a list from two items
81	*
82	* @param obj0
83	* @param obj1
84	* @return a List containing the two items
85	*/
86	private static List createList(Object obj0, Object obj1)
87	{
88	List list = new ArrayList();
89	list.add(obj0);
90	list.add(obj1);
91	return list;
92	}
93
94	/**
95	* Creates a list from two items
96	*
97	* @param obj0
98	* @param obj1
99	* @return a List containing the two items
100	*/
101	private static List createList(Object obj0, Object obj1, Object obj2)
102	{
103	List list = new ArrayList();
104	list.add(obj0);
105	list.add(obj1);
106	list.add(obj2);
107	return list;
108	}
109
110	private GeometryFactory geomFactory;
111	private boolean skipEmpty = false;
112	private Collection inputGeoms;
113
114	/**
115	* Creates a new combiner for a collection of geometries
116	*
117	* @param geoms the geometries to combine
118	*/
119	public GeometryCombiner(Collection geoms)
120	{
121	geomFactory = extractFactory(geoms);
122	this.inputGeoms = geoms;
123	}
124
125	/**
126	* Extracts the GeometryFactory used by the geometries in a collection
127	*
128	* @param geoms
129	* @return a GeometryFactory
130	*/
131	public static GeometryFactory extractFactory(Collection geoms) {
132	if (geoms.isEmpty())
133	return null;
134	return ((Geometry) geoms.iterator().next()).getFactory();
135	}
136
137	/**
138	* Computes the combination of the input geometries
139	* to produce the most appropriate {@link Geometry} or {@link GeometryCollection}
140	*
141	* @return a Geometry which is the combination of the inputs
142	*/
143	public Geometry combine()
144	{
145	List elems = new ArrayList();
146	for (Iterator i = inputGeoms.iterator(); i.hasNext(); ) {
147	Geometry g = (Geometry) i.next();
148	extractElements(g, elems);
149	}
150
151	if (elems.size() == 0) {
152	if (geomFactory != null) {
153	// return an empty GC
154	return geomFactory.createGeometryCollection();
155	}
156	return null;
157	}
158	// return the "simplest possible" geometry
159	return geomFactory.buildGeometry(elems);
160	}
161
162	private void extractElements(Geometry geom, List elems)
163	{
164	if (geom == null)
165	return;
166
167	for (int i = 0; i < geom.getNumGeometries(); i++) {
168	Geometry elemGeom = geom.getGeometryN(i);
169	if (skipEmpty && elemGeom.isEmpty())
170	continue;
171	elems.add(elemGeom);
172	}
173	}
174
175	}
176