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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    *      https://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  
18  /*
19   * This is not the original file distributed by the Apache Software Foundation
20   * It has been modified by the Hipparchus project
21   */
22  package org.hipparchus.geometry.euclidean.twod;
23  
24  import org.hipparchus.geometry.Point;
25  import org.hipparchus.util.FastMath;
26  
27  /** Simple container for a two-points segment.
28   */
29  public class Segment {
30  
31      /** Start point of the segment. */
32      private final Vector2D start;
33  
34      /** End point of the segment. */
35      private final Vector2D end;
36  
37      /** Line containing the segment. */
38      private final Line     line;
39  
40      /** Build a segment.
41       * @param start start point of the segment
42       * @param end end point of the segment
43       * @param tolerance of the line.
44       */
45      public Segment(final Vector2D start, final Vector2D end, final double tolerance) {
46          this(start, end, new Line(start, end, tolerance));
47      }
48  
49      /** Build a segment.
50       * @param start start point of the segment
51       * @param end end point of the segment
52       * @param line line containing the segment
53       */
54      public Segment(final Vector2D start, final Vector2D end, final Line line) {
55          this.start  = start;
56          this.end    = end;
57          this.line   = line;
58      }
59  
60      /** Get the start point of the segment.
61       * @return start point of the segment
62       */
63      public Vector2D getStart() {
64          return start;
65      }
66  
67      /** Get the end point of the segment.
68       * @return end point of the segment
69       */
70      public Vector2D getEnd() {
71          return end;
72      }
73  
74      /** Get the line containing the segment.
75       * @return line containing the segment
76       */
77      public Line getLine() {
78          return line;
79      }
80  
81      /**
82       * Get the length of the line segment.
83       *
84       * @return line segment length.
85       */
86      public double getLength() {
87          return getEnd().distance(getStart());
88      }
89  
90      /** Calculates the shortest distance from a point to this line segment.
91       * <p>
92       * If the perpendicular extension from the point to the line does not
93       * cross in the bounds of the line segment, the shortest distance to
94       * the two end points will be returned.
95       * </p>
96       *
97       * Algorithm adapted from:
98       * <a href="http://www.codeguru.com/forum/printthread.php?s=cc8cf0596231f9a7dba4da6e77c29db3&amp;t=194400&amp;pp=15&amp;page=1">
99       * Thread @ Codeguru</a>
100      *
101      * @param p to check
102      * @return distance between the instance and the point
103      */
104     public double distance(final Vector2D p) {
105         final double deltaX = end.getX() - start.getX();
106         final double deltaY = end.getY() - start.getY();
107 
108         final double r = ((p.getX() - start.getX()) * deltaX + (p.getY() - start.getY()) * deltaY) /
109                          (deltaX * deltaX + deltaY * deltaY);
110 
111         // r == 0 => P = startPt
112         // r == 1 => P = endPt
113         // r < 0 => P is on the backward extension of the segment
114         // r > 1 => P is on the forward extension of the segment
115         // 0 < r < 1 => P is on the segment
116 
117         // if point isn't on the line segment, just return the shortest distance to the end points
118         if (r < 0 || r > 1) {
119             final double dist1 = getStart().distance((Point<Euclidean2D>) p);
120             final double dist2 = getEnd().distance((Point<Euclidean2D>) p);
121 
122             return FastMath.min(dist1, dist2);
123         }
124         else {
125             // find point on line and see if it is in the line segment
126             final double px = start.getX() + r * deltaX;
127             final double py = start.getY() + r * deltaY;
128 
129             final Vector2D interPt = new Vector2D(px, py);
130             return interPt.distance((Point<Euclidean2D>) p);
131         }
132     }
133 }