1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.geometry.spherical.twod;
18
19 import org.apache.commons.geometry.euclidean.threed.Vector3D;
20 import org.apache.commons.geometry.spherical.oned.AngularInterval;
21 import org.apache.commons.geometry.spherical.oned.Point1S;
22 import org.apache.commons.numbers.core.Precision;
23
24 /** Class containing factory methods for constructing {@link GreatCircle} and {@link GreatCircleSubset} instances.
25 */
26 public final class GreatCircles {
27
28 /** Utility class; no instantiation. */
29 private GreatCircles() {
30 }
31
32 /** Create a great circle instance from its pole vector. An arbitrary u-axis is chosen.
33 * @param pole pole vector for the great circle
34 * @param precision precision context used to compare floating point values
35 * @return a great circle defined by the given pole vector
36 */
37 public static GreatCircle fromPole(final Vector3D pole, final Precision.DoubleEquivalence precision) {
38 final Vector3D.Unit u = pole.orthogonal();
39 final Vector3D.Unit v = pole.cross(u).normalize();
40 return new GreatCircle(pole.normalize(), u, v, precision);
41 }
42
43 /** Create a great circle instance from its pole vector and a vector representing the u-axis
44 * in the equator plane. The u-axis vector defines the {@code 0pi} location for the embedded
45 * subspace.
46 * @param pole pole vector for the great circle
47 * @param u u-axis direction for the equator plane
48 * @param precision precision context used to compare floating point values
49 * @return a great circle defined by the given pole vector and u-axis direction
50 */
51 public static GreatCircle fromPoleAndU(final Vector3D pole, final Vector3D u,
52 final Precision.DoubleEquivalence precision) {
53
54 final Vector3D.Unit unitPole = pole.normalize();
55 final Vector3D.Unit unitX = pole.orthogonal(u);
56 final Vector3D.Unit unitY = pole.cross(u).normalize();
57
58 return new GreatCircle(unitPole, unitX, unitY, precision);
59 }
60
61 /** Create a great circle instance from two points on the circle. The u-axis of the
62 * instance points to the location of the first point. The orientation of the circle
63 * is along the shortest path between the two points.
64 * @param a first point on the great circle
65 * @param b second point on the great circle
66 * @param precision precision context used to compare floating point values
67 * @return great circle instance containing the given points
68 * @throws IllegalArgumentException if either of the given points is NaN or infinite, or if the given points are
69 * equal or antipodal as evaluated by the given precision context
70 */
71 public static GreatCircle fromPoints(final Point2S a, final Point2S b,
72 final Precision.DoubleEquivalence precision) {
73
74 if (!a.isFinite() || !b.isFinite()) {
75 throw new IllegalArgumentException("Invalid points for great circle: " + a + ", " + b);
76 }
77
78 String err = null;
79
80 final double dist = a.distance(b);
81 if (precision.eqZero(dist)) {
82 err = "equal";
83 } else if (precision.eq(dist, Math.PI)) {
84 err = "antipodal";
85 }
86
87 if (err != null) {
88 throw new IllegalArgumentException("Cannot create great circle from points " + a + " and " + b +
89 ": points are " + err);
90 }
91
92 final Vector3D.Unit u = a.getVector().normalize();
93 final Vector3D.Unit pole = u.cross(b.getVector()).normalize();
94 final Vector3D.Unit v = pole.cross(u).normalize();
95
96 return new GreatCircle(pole, u, v, precision);
97 }
98
99 /** Construct an arc along the shortest path between the given points. The underlying
100 * great circle is oriented in the direction from {@code start} to {@code end}.
101 * @param start start point for the interval
102 * @param end end point point for the interval
103 * @param precision precision context used to compare floating point numbers
104 * @return an arc representing the shortest path between the given points
105 * @throws IllegalArgumentException if either of the given points is NaN or infinite, or if the given
106 * points are equal or antipodal as evaluated by the given precision context
107 * @see GreatCircles#fromPoints(Point2S, Point2S, org.apache.commons.numbers.core.Precision.DoubleEquivalence)
108 */
109 public static GreatArc arcFromPoints(final Point2S start, final Point2S end,
110 final Precision.DoubleEquivalence precision) {
111 final GreatCircle circle = GreatCircles.fromPoints(start, end, precision);
112
113 final Point1S subspaceStart = circle.toSubspace(start);
114 final Point1S subspaceEnd = circle.toSubspace(end);
115 final AngularInterval.Convex interval = AngularInterval.Convex.of(subspaceStart, subspaceEnd, precision);
116
117 return arcFromInterval(circle, interval);
118 }
119
120 /** Construct an arc from a great circle and an angular interval.
121 * @param circle circle defining the arc
122 * @param interval interval representing the portion of the circle contained
123 * in the arc
124 * @return an arc created from the given great circle and interval
125 */
126 public static GreatArc arcFromInterval(final GreatCircle circle, final AngularInterval.Convex interval) {
127 return new GreatArc(circle, interval);
128 }
129
130 /** Validate that the actual great circle is equivalent to the expected great circle,
131 * throwing an exception if not.
132 * @param expected the expected great circle
133 * @param actual the actual great circle
134 * @throws IllegalArgumentException if the actual great circle is not equivalent to the
135 * expected great circle
136 */
137 static void validateGreatCirclesEquivalent(final GreatCircle expected, final GreatCircle actual) {
138 if (!expected.eq(actual, expected.getPrecision())) {
139 throw new IllegalArgumentException("Arguments do not represent the same great circle. Expected " +
140 expected + " but was " + actual + ".");
141 }
142 }
143 }