Calculates the absolute orientation of a given vector. - Java java.lang

Java examples for java.lang:Math Vector

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Description

Calculates the absolute orientation of a given vector.

Demo Code


//package com.java2s;

import java.awt.geom.Point2D;

public class Main {
    /** A quarter pi. */
    public static final double M_PI_4 = Math.PI * 0.25;
    /** A double pi. */
    public static final double M_2_PI = 2.0 * Math.PI;

    /**/*from w  ww .  ja va  2  s .  com*/
     * Calculates the absolute orientation of a given vector.
     * 
     * @param vec The vector.
     * @return The angle from this vector to the x-axis in counter-clockwise or
     *         negative y-axis order. The range is from
     *         {@code 0.0 - 2.0 * Math.PI}. The vector (0, 0) results in an angle
     *         of <code>0</code>. Note that positive y direction points downwards.
     */
    public static double getOrientation(final Point2D vec) {
        final double x = vec.getX();
        final double y = -vec.getY();
        if (x == 0.0)
            return Math.PI * (y > 0.0 ? 0.5 : 1.5);
        return (x < 0 ? Math.PI : (y < 0 ? M_2_PI : 0)) + fastArcTan(y / x);
    }

    /**
     * A fast implementation of {@link Math#atan(double)}. The maximum error is
     * <code>0.0015</code> radians. The behavior is the same as the library
     * function. The algorithm comes from:
     * <em>"Efficient approximations for the arctangent function",
     * Rajan, S. Sichun Wang Inkol, R. Joyal, A., May 2006</em>
     * 
     * @param a The value whose arc tangent is to be returned.
     * @return The arc tangent of the argument.
     * @see Math#atan(double)
     */
    public static double fastArcTan(final double a) {
        if (a < -1 || a > 1)
            return Math.atan(a);
        return M_PI_4 * a - a * (Math.abs(a) - 1)
                * (0.2447 + 0.0663 * Math.abs(a));
    }
}

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