Class RandomPointsInGridBuilder

1	/*
2	* Copyright (c) 2016 Martin Davis.
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.shape.random;
14
15	import org.locationtech.jts.geom.Coordinate;
16	import org.locationtech.jts.geom.Geometry;
17	import org.locationtech.jts.geom.GeometryFactory;
18	import org.locationtech.jts.geom.MultiPoint;
19	import org.locationtech.jts.math.MathUtil;
20	import org.locationtech.jts.shape.GeometricShapeBuilder;
21
22
23	/**
24	* Creates random point sets
25	* where the points are constrained to lie in the cells of a grid.
26	*
27	* @author mbdavis
28	*
29	*/
30	public class RandomPointsInGridBuilder
31	extends GeometricShapeBuilder
32	{
33	private boolean isConstrainedToCircle = false;
34	private double gutterFraction = 0;
35
36	/**
37	* Create a builder which will create shapes using the default
38	* {@link GeometryFactory}.
39	*/
40	public RandomPointsInGridBuilder()
41	{
42	super(new GeometryFactory());
43	}
44
45	/**
46	* Create a builder which will create shapes using the given
47	* {@link GeometryFactory}.
48	*
49	* @param geomFact the factory to use
50	*/
51	public RandomPointsInGridBuilder(GeometryFactory geomFact)
52	{
53	super(geomFact);
54	}
55
56	/**
57	* Sets whether generated points are constrained to lie
58	* within a circle contained within each grid cell.
59	* This provides greater separation between points
60	* in adjacent cells.
61	* <p>
62	* The default is to not be constrained to a circle.
63	* @param isConstrainedToCircle
64	*/
65	public void setConstrainedToCircle(boolean isConstrainedToCircle)
66	{
67	this.isConstrainedToCircle = isConstrainedToCircle;
68	}
69
70	/**
71	* Sets the fraction of the grid cell side which will be treated as
72	* a gutter, in which no points will be created.
73	* The provided value is clamped to the range [0.0, 1.0].
74	*
75	* @param gutterFraction
76	*/
77	public void setGutterFraction(double gutterFraction)
78	{
79	this.gutterFraction = gutterFraction;
80	}
81
82	/**
83	* Gets the {@link MultiPoint} containing the generated point
84	*
85	* @return a MultiPoint
86	*/
87	public Geometry getGeometry()
88	{
89	int nCells = (int) Math.sqrt(numPts);
90	// ensure that at least numPts points are generated
91	if (nCells * nCells < numPts)
92	nCells += 1;
93
94	double gridDX = getExtent().getWidth() / nCells;
95	double gridDY = getExtent().getHeight() / nCells;
96
97	double gutterFrac = MathUtil.clamp(gutterFraction, 0.0, 1.0);
98	double gutterOffsetX = gridDX * gutterFrac/2;
99	double gutterOffsetY = gridDY * gutterFrac/2;
100	double cellFrac = 1.0 - gutterFrac;
101	double cellDX = cellFrac * gridDX;
102	double cellDY = cellFrac * gridDY;
103
104	Coordinate[] pts = new Coordinate[nCells * nCells];
105	int index = 0;
106	for (int i = 0; i < nCells; i++) {
107	for (int j = 0; j < nCells; j++) {
108	double orgX = getExtent().getMinX() + i * gridDX + gutterOffsetX;
109	double orgY = getExtent().getMinY() + j * gridDY + gutterOffsetY;
110	pts[index++] = randomPointInCell(orgX, orgY, cellDX, cellDY);
111	}
112	}
113	return geomFactory.createMultiPointFromCoords(pts);
114	}
115
116	private Coordinate randomPointInCell(double orgX, double orgY, double xLen, double yLen)
117	{
118	if (isConstrainedToCircle) {
119	return randomPointInCircle(
120	orgX,
121	orgY,
122	xLen, yLen);
123	}
124	return randomPointInGridCell(orgX, orgY, xLen, yLen);
125	}
126
127	private Coordinate randomPointInGridCell(double orgX, double orgY, double xLen, double yLen)
128	{
129	double x = orgX + xLen * Math.random();
130	double y = orgY + yLen * Math.random();
131	return createCoord(x, y);
132	}
133
134	private static Coordinate randomPointInCircle(double orgX, double orgY, double width, double height)
135	{
136	double centreX = orgX + width/2;
137	double centreY = orgY + height/2;
138
139	double rndAng = 2 * Math.PI * Math.random();
140	double rndRadius = Math.random();
141	// use square root of radius, since area is proportional to square of radius
142	double rndRadius2 = Math.sqrt(rndRadius);
143	double rndX = width/2 * rndRadius2 * Math.cos(rndAng);
144	double rndY = height/2 * rndRadius2 * Math.sin(rndAng);
145
146	double x0 = centreX + rndX;
147	double y0 = centreY + rndY;
148	return new Coordinate(x0, y0);
149	}
150
151	}
152