    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017    package org.apache.commons.math3.geometry.euclidean.twod;
    018
    019    import org.apache.commons.math3.util.FastMath;
    020
    021    /** Simple container for a two-points segment.
    022     * @version $Id: Segment.java 1422195 2012-12-15 06:45:18Z psteitz $
    023     * @since 3.0
    024     */
    025    public class Segment {
    026
    027        /** Start point of the segment. */
    028        private final Vector2D start;
    029
    030        /** End point of the segments. */
    031        private final Vector2D end;
    032
    033        /** Line containing the segment. */
    034        private final Line     line;
    035
    036        /** Build a segment.
    037         * @param start start point of the segment
    038         * @param end end point of the segment
    039         * @param line line containing the segment
    040         */
    041        public Segment(final Vector2D start, final Vector2D end, final Line line) {
    042            this.start  = start;
    043            this.end    = end;
    044            this.line   = line;
    045        }
    046
    047        /** Get the start point of the segment.
    048         * @return start point of the segment
    049         */
    050        public Vector2D getStart() {
    051            return start;
    052        }
    053
    054        /** Get the end point of the segment.
    055         * @return end point of the segment
    056         */
    057        public Vector2D getEnd() {
    058            return end;
    059        }
    060
    061        /** Get the line containing the segment.
    062         * @return line containing the segment
    063         */
    064        public Line getLine() {
    065            return line;
    066        }
    067
    068        /** Calculates the shortest distance from a point to this line segment.
    069         * <p>
    070         * If the perpendicular extension from the point to the line does not
    071         * cross in the bounds of the line segment, the shortest distance to
    072         * the two end points will be returned.
    073         * </p>
    074         *
    075         * Algorithm adapted from:
    076         * <a href="http://www.codeguru.com/forum/printthread.php?s=cc8cf0596231f9a7dba4da6e77c29db3&t=194400&pp=15&page=1">
    077         * Thread @ Codeguru</a>
    078         *
    079         * @param p to check
    080         * @return distance between the instance and the point
    081         * @since 3.1
    082         */
    083        public double distance(final Vector2D p) {
    084            final double deltaX = end.getX() - start.getX();
    085            final double deltaY = end.getY() - start.getY();
    086
    087            final double r = ((p.getX() - start.getX()) * deltaX + (p.getY() - start.getY()) * deltaY) /
    088                             (deltaX * deltaX + deltaY * deltaY);
    089
    090            // r == 0 => P = startPt
    091            // r == 1 => P = endPt
    092            // r < 0 => P is on the backward extension of the segment
    093            // r > 1 => P is on the forward extension of the segment
    094            // 0 < r < 1 => P is on the segment
    095
    096            // if point isn't on the line segment, just return the shortest distance to the end points
    097            if (r < 0 || r > 1) {
    098                final double dist1 = getStart().distance(p);
    099                final double dist2 = getEnd().distance(p);
    100
    101                return FastMath.min(dist1, dist2);
    102            }
    103            else {
    104                // find point on line and see if it is in the line segment
    105                final double px = start.getX() + r * deltaX;
    106                final double py = start.getY() + r * deltaY;
    107
    108                final Vector2D interPt = new Vector2D(px, py);
    109                return interPt.distance(p);
    110            }
    111        }
    112    }