Find the angle between three points. - Java java.lang

Java examples for java.lang:Math Geometry

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Description

Find the angle between three points.

Demo Code



public class Main{
    /**/*w w w  . j a  va  2s  .c o  m*/
     * Find the angle between three points. P0 is center point
     *
     * @param p0, p1, p2 Three points finding angle between [x,y,z].
     * @return Angle (in radians) between given points.
     */
    public static double computeAngle(double[] p0, double[] p1, double[] p2) {
        double[] v0 = GeometryUtils.createVector(p0, p1);
        double[] v1 = GeometryUtils.createVector(p0, p2);

        double dotProduct = GeometryUtils.computeDotProduct(v0, v1);

        double length1 = GeometryUtils.length(v0);
        double length2 = GeometryUtils.length(v1);

        double denominator = length1 * length2;

        double product = denominator != 0.0 ? dotProduct / denominator
                : 0.0;

        double angle = Math.acos(product);

        return angle;
    }
    /**
     * Construct the vector specified by two points.
     *
     * @param p0, p1 Points the construct vector between [x,y,z].
     * @return v Vector from p0 to p1 [x,y,z].
     */
    public static double[] createVector(double[] p0, double[] p1) {
        double v[] = { p1[0] - p0[0], p1[1] - p0[1], p1[2] - p0[2] };
        return v;
    }
    /**
     * Compute the dot product (a scalar) between two vectors.
     *
     * @param v0, v1 Vectors to compute dot product between [x,y,z].
     * @return Dot product of given vectors.
     */
    public static double computeDotProduct(double[] v0, double[] v1) {
        return v0[0] * v1[0] + v0[1] * v1[1] + v0[2] * v1[2];
    }
    /**
     * Return the length of a vector.
     *
     * @param v Vector to compute length of [x,y,z].
     * @return Length of vector.
     */
    public static double length(double[] v) {
        return Math.sqrt(v[0] * v[0] + v[1] * v[1] + v[2] * v[2]);
    }
    /**
     * Compute distance between two points.
     *
     * @param p0, p1 Points to compute distance between [x,y,z].
     * @return Distance between points.
     */
    public static double length(double[] p0, double[] p1) {
        double[] v = GeometryUtils.createVector(p0, p1);
        return length(v);
    }
    /**
     * Compute the length of the line from (x0,y0) to (x1,y1)
     *
     * @param x0, y0 First line end point.
     * @param x1, y1 Second line end point.
     * @return Length of line from (x0,y0) to (x1,y1).
     */
    public static double length(int x0, int y0, int x1, int y1) {
        return GeometryUtils.length((double) x0, (double) y0, (double) x1,
                (double) y1);
    }
    /**
     * Compute the length of the line from (x0,y0) to (x1,y1)
     *
     * @param x0, y0 First line end point.
     * @param x1, y1 Second line end point.
     * @return Length of line from (x0,y0) to (x1,y1).
     */
    public static double length(double x0, double y0, double x1, double y1) {
        double dx = x1 - x0;
        double dy = y1 - y0;

        return Math.sqrt(dx * dx + dy * dy);
    }
    /**
     * Compute the length of a polyline.
     *
     * @param x, y Arrays of x,y coordinates
     * @param nPoints Number of elements in the above.
     * @param isClosed True if this is a closed polygon, false otherwise
     * @return Length of polyline defined by x, y and nPoints.
     */
    public static double length(int[] x, int[] y, boolean isClosed) {
        double length = 0.0;

        int nPoints = x.length;
        for (int i = 0; i < nPoints - 1; i++) {
            length += GeometryUtils.length(x[i], y[i], x[i + 1], y[i + 1]);
        }

        // Add last leg if this is a polygon
        if (isClosed && nPoints > 1) {
            length += GeometryUtils.length(x[nPoints - 1], y[nPoints - 1],
                    x[0], y[0]);
        }

        return length;
    }
}

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