Class BufferResultValidator

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	package org.locationtech.jts.operation.buffer.validate;
13
14	import org.locationtech.jts.geom.Coordinate;
15	import org.locationtech.jts.geom.Envelope;
16	import org.locationtech.jts.geom.Geometry;
17	import org.locationtech.jts.geom.MultiPolygon;
18	import org.locationtech.jts.geom.Polygon;
19
20	/**
21	* Validates that the result of a buffer operation
22	* is geometrically correct, within a computed tolerance.
23	* <p>
24	* This is a heuristic test, and may return false positive results
25	* (I.e. it may fail to detect an invalid result.)
26	* It should never return a false negative result, however
27	* (I.e. it should never report a valid result as invalid.)
28	* <p>
29	* This test may be (much) more expensive than the original
30	* buffer computation.
31	*
32	* @author Martin Davis
33	*/
34	public class BufferResultValidator
35	{
36	private static boolean VERBOSE = false;
37
38	/**
39	* Maximum allowable fraction of buffer distance the
40	* actual distance can differ by.
41	* 1% sometimes causes an error - 1.2% should be safe.
42	*/
43	private static final double MAX_ENV_DIFF_FRAC = .012;
44
45	public static boolean isValid(Geometry g, double distance, Geometry result)
46	{
47	BufferResultValidator validator = new BufferResultValidator(g, distance, result);
48	if (validator.isValid())
49	return true;
50	return false;
51	}
52
53	/**
54	* Checks whether the geometry buffer is valid,
55	* and returns an error message if not.
56	*
57	* @param g
58	* @param distance
59	* @param result
60	* @return an appropriate error message
61	* or null if the buffer is valid
62	*/
63	public static String isValidMsg(Geometry g, double distance, Geometry result)
64	{
65	BufferResultValidator validator = new BufferResultValidator(g, distance, result);
66	if (! validator.isValid())
67	return validator.getErrorMessage();
68	return null;
69	}
70
71	private Geometry input;
72	private double distance;
73	private Geometry result;
74	private boolean isValid = true;
75	private String errorMsg = null;
76	private Coordinate errorLocation = null;
77	private Geometry errorIndicator = null;
78
79	public BufferResultValidator(Geometry input, double distance, Geometry result)
80	{
81	this.input = input;
82	this.distance = distance;
83	this.result = result;
84	}
85
86	public boolean isValid()
87	{
88	checkPolygonal();
89	if (! isValid) return isValid;
90	checkExpectedEmpty();
91	if (! isValid) return isValid;
92	checkEnvelope();
93	if (! isValid) return isValid;
94	checkArea();
95	if (! isValid) return isValid;
96	checkDistance();
97	return isValid;
98	}
99
100	public String getErrorMessage()
101	{
102	return errorMsg;
103	}
104
105	public Coordinate getErrorLocation()
106	{
107	return errorLocation;
108	}
109
110	/**
111	* Gets a geometry which indicates the location and nature of a validation failure.
112	* <p>
113	* If the failure is due to the buffer curve being too far or too close
114	* to the input, the indicator is a line segment showing the location and size
115	* of the discrepancy.
116	*
117	* @return a geometric error indicator
118	* or null if no error was found
119	*/
120	public Geometry getErrorIndicator()
121	{
122	return errorIndicator;
123	}
124
125	private void report(String checkName)
126	{
127	if (! VERBOSE) return;
128	System.out.println("Check " + checkName + ": "
129	+ (isValid ? "passed" : "FAILED"));
130	}
131
132	private void checkPolygonal()
133	{
134	if (! (result instanceof Polygon
135	\|\| result instanceof MultiPolygon))
136	isValid = false;
137	errorMsg = "Result is not polygonal";
138	errorIndicator = result;
139	report("Polygonal");
140	}
141
142	private void checkExpectedEmpty()
143	{
144	// can't check areal features
145	if (input.getDimension() >= 2) return;
146	// can't check positive distances
147	if (distance > 0.0) return;
148
149	// at this point can expect an empty result
150	if (! result.isEmpty()) {
151	isValid = false;
152	errorMsg = "Result is non-empty";
153	errorIndicator = result;
154	}
155	report("ExpectedEmpty");
156	}
157
158	private void checkEnvelope()
159	{
160	if (distance < 0.0) return;
161
162	double padding = distance * MAX_ENV_DIFF_FRAC;
163	if (padding == 0.0) padding = 0.001;
164
165	Envelope expectedEnv = new Envelope(input.getEnvelopeInternal());
166	expectedEnv.expandBy(distance);
167
168	Envelope bufEnv = new Envelope(result.getEnvelopeInternal());
169	bufEnv.expandBy(padding);
170
171	if (! bufEnv.contains(expectedEnv)) {
172	isValid = false;
173	errorMsg = "Buffer envelope is incorrect";
174	errorIndicator = input.getFactory().toGeometry(bufEnv);
175	}
176	report("Envelope");
177	}
178
179	private void checkArea()
180	{
181	double inputArea = input.getArea();
182	double resultArea = result.getArea();
183
184	if (distance > 0.0
185	&& inputArea > resultArea) {
186	isValid = false;
187	errorMsg = "Area of positive buffer is smaller than input";
188	errorIndicator = result;
189	}
190	if (distance < 0.0
191	&& inputArea < resultArea) {
192	isValid = false;
193	errorMsg = "Area of negative buffer is larger than input";
194	errorIndicator = result;
195	}
196	report("Area");
197	}
198
199	private void checkDistance()
200	{
201	BufferDistanceValidator distValid = new BufferDistanceValidator(input, distance, result);
202	if (! distValid.isValid()) {
203	isValid = false;
204	errorMsg = distValid.getErrorMessage();
205	errorLocation = distValid.getErrorLocation();
206	errorIndicator = distValid.getErrorIndicator();
207	}
208	report("Distance");
209	}
210	}
211