GeometryUtils.java

/* This program 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 3 of
 the License, or (at your option) any later version.

 This program 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 this program.  If not, see <http://www.gnu.org/licenses/>. */

package org.opentripplanner.common.geometry;

import org.opentripplanner.common.model.P2;

import com.vividsolutions.jts.geom.Coordinate;
import com.vividsolutions.jts.geom.CoordinateSequenceFactory;
import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.GeometryFactory;
import com.vividsolutions.jts.geom.LineString;
import com.vividsolutions.jts.linearref.LinearLocation;
import com.vividsolutions.jts.linearref.LocationIndexedLine;

public class GeometryUtils {

    private static CoordinateSequenceFactory csf = new Serializable2DPackedCoordinateSequenceFactory();
    private static GeometryFactory gf = new GeometryFactory(csf);

    public static LineString makeLineString(double... coords) {
        GeometryFactory factory = getGeometryFactory();
        Coordinate [] coordinates = new Coordinate[coords.length / 2];
        for (int i = 0; i < coords.length; i+=2) {
            coordinates[i / 2] = new Coordinate(coords[i], coords[i+1]);
        }
        return factory.createLineString(coordinates);
    }

    public static GeometryFactory getGeometryFactory() {
        return gf;
    }
    
    /**
     * Splits the input geometry into two LineStrings at the given point.
     */
    public static P2<LineString> splitGeometryAtPoint(Geometry geometry, Coordinate nearestPoint) {
        LocationIndexedLine line = new LocationIndexedLine(geometry);
        LinearLocation l = line.indexOf(nearestPoint);

        LineString beginning = (LineString) line.extractLine(line.getStartIndex(), l);
        LineString ending = (LineString) line.extractLine(l, line.getEndIndex());

        return new P2<LineString>(beginning, ending);
    }
    
    /**
     * Returns the chunk of the given geometry between the two given coordinates.
     * 
     * Assumes that "second" is after "first" along the input geometry.
     */
    public static LineString getInteriorSegment(Geometry geomerty, Coordinate first,
            Coordinate second) {
        P2<LineString> splitGeom = GeometryUtils.splitGeometryAtPoint(geomerty, first);
        splitGeom = GeometryUtils.splitGeometryAtPoint(splitGeom.getSecond(), second);
        return splitGeom.getFirst();
    }

    /**
     * Adapted from com.vividsolutions.jts.geom.LineSegment 
     * Combines segmentFraction and projectionFactor methods.
     */
    public static double segmentFraction(double x0, double y0, double x1, double y1, 
            double xp, double yp, double xscale) {
        // Use comp.graphics.algorithms Frequently Asked Questions method
        double dx = (x1 - x0) * xscale;
        double dy = y1 - y0;
        double len2 = dx * dx + dy * dy;
        // this fixes a (reported) divide by zero bug in JTS when line segment has 0 length
        if (len2 == 0)
            return 0;
        double r = ( (xp - x0) * xscale * dx + (yp - y0) * dy ) / len2;
        if (r < 0.0)
            return 0.0;
        else if (r > 1.0)
            return 1.0;
        return r;
      }
}