Class HilbertCurveBuilder

1	/*
2	* Copyright (c) 2019 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.fractal;
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.LineSegment;
19	import org.locationtech.jts.geom.LineString;
20	import org.locationtech.jts.shape.GeometricShapeBuilder;
21	import static org.locationtech.jts.shape.fractal.HilbertCode.*;
22
23	/**
24	* Generates a {@link LineString} representing the Hilbert Curve
25	* at a given level.
26	*
27	* @author Martin Davis
28	* @see HilbertCode
29	*/
30	public class HilbertCurveBuilder
31	extends GeometricShapeBuilder
32	{
33	private int order = -1;
34
35	/**
36	* Creates a new instance using the provided {@link GeometryFactory}.
37	*
38	* @param geomFactory the geometry factory to use
39	*/
40	public HilbertCurveBuilder(GeometryFactory geomFactory)
41	{
42	super(geomFactory);
43	// use a null extent to indicate no transformation
44	// (may be set by client)
45	extent = null;
46	}
47
48	/**
49	* Sets the level of curve to generate.
50	* The level must be in the range [0 - 16].
51	*
52	* @param level the order of the curve
53	*/
54	public void setLevel(int level) {
55	this.numPts = size(level); }
56
57	@Override
58	public Geometry getGeometry() {
59	int level = level(numPts);
60	int nPts = size(level);
61
62	double scale = 1;
63	double baseX = 0;
64	double baseY = 0;
65	if (extent != null) {
66	LineSegment baseLine = getSquareBaseLine();
67	baseX = baseLine.minX();
68	baseY = baseLine.minY();
69	double width = baseLine.getLength();
70	int maxOrdinate = maxOrdinate(level);
71	scale = width / maxOrdinate;
72	}
73
74	Coordinate[] pts = new Coordinate[nPts];
75	for (int i = 0; i < nPts; i++) {
76	Coordinate pt = decode(level, i);
77	double x = transform(pt.getX(), scale, baseX );
78	double y = transform(pt.getY(), scale, baseY );
79	pts[i] = new Coordinate(x, y);
80	}
81	return geomFactory.createLineString(pts);
82	}
83
84	private static double transform(double val, double scale, double offset) {
85	return val * scale + offset;
86	}
87
88	}
89