Compute the angle between the vector (1,0) and the given vector. - Java java.lang

Java examples for java.lang:Math Vector

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Description

Compute the angle between the vector (1,0) and the given vector.

Demo Code

/* /*w w  w  .j av a 2 s  .  c om*/
 * $Id$
 * 
 * Copyright (c) 2007-13 Stephane GALLAND.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * This program is free software; you can redistribute it and/or modify
 */
import javax.vecmath.Vector2d;

public class Main{
    /** Compute the angle between the vector (1,0) and the given vector.
     * 
     * @param orientation
     * @return the angle
     */
    public static double toOrientationAngle(Vector2d orientation) {
        return signedAngle(new Vector2d(1, 0), orientation);
    }
    /** Replies the angle between the vector v1 and v2.
     * <p>
     * The replied angle is the smallest rotation angle to turn v1 to be equals to
     * v2. 
     * <p>
     * Assumed that: <ul>
     * <li>signedAngle(v1,v2) == -signedAngle(v2,v2)</li>
     * <li>v2.equals( turnVector( v1, signedAngle(v1,v2) ) )</li>
     * </ul>
     * 
     * @param v1
     * @param v2
     * @return the signed angle between v1 and v2
     */
    public static double signedAngle(Vector2d v1, Vector2d v2) {
        Vector2d a = new Vector2d(v1);
        if (a.length() == 0)
            return Double.NaN;
        Vector2d b = new Vector2d(v2);
        if (b.length() == 0)
            return Double.NaN;
        a.normalize();
        b.normalize();

        double cos = a.x * b.x + a.y * b.y;
        // A x B = |A|.|B|.sin(theta).N = sin(theta) (where N is the unit vector perpendicular to plane AB)
        double sin = a.x * b.y - a.y * b.x;

        double angle = Math.atan2(sin, cos);

        return angle;
    }
}

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