Circle Line Intersections - Java java.lang

Java examples for java.lang:Math Geometry Line

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Description

Circle Line Intersections

Demo Code


import static java.lang.Math.sqrt;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;

public class Main{
    public static List<Point> CircleLineIntersections(List<Line> lines,
            Circle cir) {/*from  www.j  a v  a 2  s  . c o  m*/
        List<Point> arr = new ArrayList<Point>();
        //int n = 0;
        //do {
        for (int i = 0; i < lines.size(); i++) {
            List<Point> a = CircleLineIntersection(lines.get(i).pt1,
                    lines.get(i).pt2, cir.center, cir.radius);
            if (a != null) {
                arr.addAll(a);
            }
        }
        //n++;
        //} while (n < lines.size());
        return arr;
    }
    /**
     * 
     * Code adapted from Paul Bourke:
     * http://local.wasp.uwa.edu.au/~pbourke/geometry/sphereline/raysphere.c
     * 
     * @param A
     * @param B
     * @param C
     * @param rad
     * @return
     */

    public static List<Point> CircleLineIntersection(Point A, Point B,
            Point C, int rad) {
        // boolean circleLineIntersect(float x1, float y1, float x2, float y2,
        // float cx, float cy, float cr ) {
        float dx = B.x - A.x;
        float dy = B.y - A.y;
        float a = dx * dx + dy * dy;
        float b = 2 * (dx * (A.x - C.x) + dy * (A.y - C.y));
        float c = C.x * C.x + C.y * C.y;
        c += A.x * A.x + A.y * A.y;
        c -= 2 * (C.x * A.x + C.y * A.y);
        c -= rad * rad;
        float bb4ac = b * b - 4 * a * c;
        // println(bb4ac);

        if (bb4ac < 0) // Not intersecting
            return null;
        //
        float mu1 = (float) (-b + sqrt(b * b - 4 * a * c)) / (2 * a);
        float ix1 = A.x + mu1 * (dx);
        float iy1 = A.y + mu1 * (dy);
        float mu2 = (float) (-b - sqrt(b * b - 4 * a * c)) / (2 * a);
        float ix2 = A.x + mu2 * (dx);
        float iy2 = A.y + mu2 * (dy);
        //
        // // if ((mu1 > 1 && mu2 < 0) || (mu1 < 0 && mu2 > 1))
        // // return null;
        //
        Point p1 = new Point(ix1, iy1);
        Point p2 = new Point(ix2, iy2);
        ArrayList arr = new ArrayList();
        arr.add(p1);
        arr.add(p2);

        return arr;

    }
}

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