/* * The JTS Topology Suite is a collection of Java classes that * implement the fundamental operations required to validate a given * geo-spatial data set to a known topological specification. * * Copyright (C) 2001 Vivid Solutions * * 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 * * For more information, contact: * * Vivid Solutions * Suite #1A * 2328 Government Street * Victoria BC V8T 5G5 * Canada * * (250)385-6040 * www.vividsolutions.com */ package com.vividsolutions.jts.operation.overlay.validate; import java.util.*; import com.vividsolutions.jts.geom.*; import com.vividsolutions.jts.geom.util.*; /** * Generates points offset by a given distance * from both sides of the midpoint of * all segments in a {@link Geometry}. * Can be used to generate probe points for * determining whether a polygonal overlay result * is incorrect. * The input geometry may have any orientation for its rings, * but {@link #setSidesToGenerate(boolean, boolean)} is * only meaningful if the orientation is known. * * @author Martin Davis * @version 1.7 */ public class OffsetPointGenerator { private Geometry g; private boolean doLeft = true; private boolean doRight = true; public OffsetPointGenerator(Geometry g) { this.g = g; } /** * Set the sides on which to generate offset points. * * @param doLeft * @param doRight */ public void setSidesToGenerate(boolean doLeft, boolean doRight) { this.doLeft = doLeft; this.doRight = doRight; } /** * Gets the computed offset points. * * @return List<Coordinate> */ public List getPoints(double offsetDistance) { List offsetPts = new ArrayList(); List lines = LinearComponentExtracter.getLines(g); for (Iterator i = lines.iterator(); i.hasNext(); ) { LineString line = (LineString) i.next(); extractPoints(line, offsetDistance, offsetPts); } //System.out.println(toMultiPoint(offsetPts)); return offsetPts; } private void extractPoints(LineString line, double offsetDistance, List offsetPts) { Coordinate[] pts = line.getCoordinates(); for (int i = 0; i < pts.length - 1; i++) { computeOffsetPoints(pts[i], pts[i + 1], offsetDistance, offsetPts); } } /** * Generates the two points which are offset from the * midpoint of the segment <tt>(p0, p1)</tt> by the * <tt>offsetDistance</tt>. * * @param p0 the first point of the segment to offset from * @param p1 the second point of the segment to offset from */ private void computeOffsetPoints(Coordinate p0, Coordinate p1, double offsetDistance, List offsetPts) { double dx = p1.x - p0.x; double dy = p1.y - p0.y; double len = Math.sqrt(dx * dx + dy * dy); // u is the vector that is the length of the offset, in the direction of the segment double ux = offsetDistance * dx / len; double uy = offsetDistance * dy / len; double midX = (p1.x + p0.x) / 2; double midY = (p1.y + p0.y) / 2; if (doLeft) { Coordinate offsetLeft = new Coordinate(midX - uy, midY + ux); offsetPts.add(offsetLeft); } if (doRight) { Coordinate offsetRight = new Coordinate(midX + uy, midY - ux); offsetPts.add(offsetRight); } } }