Class CommonBitsRemover

1
2	/*
3	* Copyright (c) 2016 Vivid Solutions.
4	*
5	* All rights reserved. This program and the accompanying materials
6	* are made available under the terms of the Eclipse Public License 2.0
7	* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
8	* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
9	* and the Eclipse Distribution License is available at
10	*
11	* http://www.eclipse.org/org/documents/edl-v10.php.
12	*/
13	package org.locationtech.jts.precision;
14
15	import org.locationtech.jts.geom.Coordinate;
16	import org.locationtech.jts.geom.CoordinateFilter;
17	import org.locationtech.jts.geom.CoordinateSequence;
18	import org.locationtech.jts.geom.CoordinateSequenceFilter;
19	import org.locationtech.jts.geom.Geometry;
20
21	/**
22	* Removes common most-significant mantissa bits
23	* from one or more {@link Geometry}s.
24	* <p>
25	* The CommonBitsRemover "scavenges" precision
26	* which is "wasted" by a large displacement of the geometry
27	* from the origin.
28	* For example, if a small geometry is displaced from the origin
29	* by a large distance,
30	* the displacement increases the significant figures in the coordinates,
31	* but does not affect the <i>relative</i> topology of the geometry.
32	* Thus the geometry can be translated back to the origin
33	* without affecting its topology.
34	* In order to compute the translation without affecting
35	* the full precision of the coordinate values,
36	* the translation is performed at the bit level by
37	* removing the common leading mantissa bits.
38	* <p>
39	* If the geometry envelope already contains the origin,
40	* the translation procedure cannot be applied.
41	* In this case, the common bits value is computed as zero.
42	* <p>
43	* If the geometry crosses the Y axis but not the X axis
44	* (and <i>mutatis mutandum</i>),
45	* the common bits for Y are zero,
46	* but the common bits for X are non-zero.
47	*
48	* @version 1.7
49	*/
50	public class CommonBitsRemover
51	{
52	private Coordinate commonCoord;
53	private CommonCoordinateFilter ccFilter = new CommonCoordinateFilter();
54
55	public CommonBitsRemover()
56	{
57	}
58
59	/**
60	* Add a geometry to the set of geometries whose common bits are
61	* being computed. After this method has executed the
62	* common coordinate reflects the common bits of all added
63	* geometries.
64	*
65	* @param geom a Geometry to test for common bits
66	*/
67	public void add(Geometry geom)
68	{
69	geom.apply(ccFilter);
70	commonCoord = ccFilter.getCommonCoordinate();
71	}
72
73	/**
74	* The common bits of the Coordinates in the supplied Geometries.
75	*/
76	public Coordinate getCommonCoordinate() { return commonCoord; }
77
78	/**
79	* Removes the common coordinate bits from a Geometry.
80	* The coordinates of the Geometry are changed.
81	*
82	* @param geom the Geometry from which to remove the common coordinate bits
83	* @return the shifted Geometry
84	*/
85	public Geometry removeCommonBits(Geometry geom)
86	{
87	if (commonCoord.x == 0.0 && commonCoord.y == 0.0)
88	return geom;
89	Coordinate invCoord = new Coordinate(commonCoord);
90	invCoord.x = -invCoord.x;
91	invCoord.y = -invCoord.y;
92	Translater trans = new Translater(invCoord);
93	geom.apply(trans);
94	geom.geometryChanged();
95	return geom;
96	}
97
98	/**
99	* Adds the common coordinate bits back into a Geometry.
100	* The coordinates of the Geometry are changed.
101	*
102	* @param geom the Geometry to which to add the common coordinate bits
103	*/
104	public void addCommonBits(Geometry geom)
105	{
106	Translater trans = new Translater(commonCoord);
107	geom.apply(trans);
108	geom.geometryChanged();
109	}
110
111	static class CommonCoordinateFilter
112	implements CoordinateFilter
113	{
114	private CommonBits commonBitsX = new CommonBits();
115	private CommonBits commonBitsY = new CommonBits();
116
117	public void filter(Coordinate coord)
118	{
119	commonBitsX.add(coord.x);
120	commonBitsY.add(coord.y);
121	}
122
123	public Coordinate getCommonCoordinate()
124	{
125	return new Coordinate(
126	commonBitsX.getCommon(),
127	commonBitsY.getCommon());
128	}
129	}
130
131	static class Translater
132	implements CoordinateSequenceFilter
133	{
134	Coordinate trans = null;
135
136	public Translater(Coordinate trans)
137	{
138	this.trans = trans;
139	}
140
141	public void filter(CoordinateSequence seq, int i) {
142	double xp = seq.getOrdinate(i, 0) + trans.x;
143	double yp = seq.getOrdinate(i, 1) + trans.y;
144	seq.setOrdinate(i, 0, xp);
145	seq.setOrdinate(i, 1, yp);
146	}
147
148	public boolean isDone() {
149	return false;
150	}
151
152	public boolean isGeometryChanged() {
153	return true;
154	}
155
156	}
157
158	}
159