magma.util.geometry.Geometry.java Source code

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Here is the source code for magma.util.geometry.Geometry.java

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/* Copyright 2009 Hochschule Offenburg
 * Klaus Dorer, Mathias Ehret, Stefan Glaser, Thomas Huber,
 * Simon Raffeiner, Srinivasa Ragavan, Thomas Rinklin,
 * Joachim Schilling, Ingo Schindler, Rajit Shahi
 *
 * This file is part of magmaOffenburg.
 *
 * magmaOffenburg is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * magmaOffenburg 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with magmaOffenburg. If not, see <http://www.gnu.org/licenses/>.
 */
package magma.util.geometry;

import org.apache.commons.math.geometry.Vector3D;

/**
 * Utilities for geometric calculations
 * @author dorer
 */
public class Geometry {
    /**
     * Checks if the passed 2D point is inside the passed polygon
     * @param position the point to check (x,y) (it has to be in the same
     *        coordinate system as the points of the polygon
     * @param polygon corner points 2D of the polygon in clockwise direction
     * @return true if the passed point is inside the polygon
     */
    public static boolean isInsidePolygon(Vector3D position, Vector3D[] polygon) {
        int index0 = polygon.length - 1;
        int index1 = 0;
        double x2 = position.getX();
        double y2 = position.getY();
        for (int i = 0; i < polygon.length; i++) {
            double x0 = polygon[index0].getX();
            double y0 = polygon[index0].getY();
            double x1 = polygon[index1].getX();
            double y1 = polygon[index1].getY();
            // if points are clockwise then the determinant has to be positive
            // ----1 | x0 y0 1 |
            // A = - | x1 y1 1 |
            // ----2 | x2 y2 1 |
            double result = 0.5 * (x1 * y2 - y1 * x2 - x0 * y2 + y0 * x2 + x0 * y1 - y0 * x1);
            if (result > 0) {
                return false;
            }

            index0 = index1;
            index1++;
        }

        return true;
    }

    /**
     * Converts the passed points to a Vector3D array representing a polygon
     * @param points the corner points (x,y)
     * @return a Vector3D array representing a polygon
     */
    public static Vector3D[] getPolygon(double[][] points) {
        Vector3D[] polygon = new Vector3D[points.length];
        for (int i = 0; i < points.length; i++) {
            double[] point = points[i];
            polygon[i] = new Vector3D(point[0], point[1], 0);
        }
        return polygon;
    }
}