intersect Line Segment With Polygon - Java java.lang

Java examples for java.lang:Math Geometry Line

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Description

intersect Line Segment With Polygon

Demo Code


import java.awt.geom.*;
import java.util.*;

public class Main{
    public static double[][] intersectLineSegmentWithPolygon(double x1,
            double y1, double x2, double y2, double[][] polygon) {

        java.util.List intersectionList = new java.util.LinkedList();

        // intersect the line segment with each side of the polygon
        for (int i = 1; i < polygon.length; i++) {
            double[] intersection = GeometryUtils.intersectLineSegments(x1,
                    y1, x2, y2, polygon[i - 1][0], polygon[i - 1][1],
                    polygon[i][0], polygon[i][1]);
            if (intersection != null) {
                intersectionList.add(intersection);
            }//from   w  w  w. j av  a 2s . c  o m
        }

        if (intersectionList.isEmpty()) {
            return null;
        }

        // order the intersection points by increasing distance from the start point
        java.util.Collections.sort(intersectionList, new DistComp());

        // copy the coordinates of the intersection points
        double[][] intersections = new double[intersectionList.size()][2];
        for (int i = 0; i < intersections.length; ++i) {
            final double[] inter = (double[]) intersectionList.get(i);
            intersections[i][0] = inter[0];
            intersections[i][1] = inter[1];
        }
        return intersections;
    }
    public static double[] intersectLineSegments(double x1, double y1,
            double x2, double y2, double x3, double y3, double x4, double y4) {

        final double denominator = (y4 - y3) * (x2 - x1) - (x4 - x3)
                * (y2 - y1);
        if (denominator == 0.d) {
            return null; // lines are parallel
        }

        final double ua = ((x4 - x3) * (y1 - y3) - (y4 - y3) * (x1 - x3))
                / denominator;
        if (ua <= 0.d || ua >= 1.d) {
            return null; // no intersection
        }

        final double ub = ((x2 - x1) * (y1 - y3) - (y2 - y1) * (x1 - x3))
                / denominator;
        if (ub <= 0.d || ub >= 1.d) {
            return null; // no intersection
        }

        return new double[] { x1 + ua * (x2 - x1), y1 + ua * (y2 - y1), ua };
    }
}

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