/* * 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.simplify; import java.util.*; import com.vividsolutions.jts.geom.*; /** * Simplifies a linestring (sequence of points) using * the standard Douglas-Peucker algorithm. * * @version 1.7 */ class DouglasPeuckerLineSimplifier { public static Coordinate[] simplify(Coordinate[] pts, double distanceTolerance) { DouglasPeuckerLineSimplifier simp = new DouglasPeuckerLineSimplifier(pts); simp.setDistanceTolerance(distanceTolerance); return simp.simplify(); } private Coordinate[] pts; private boolean[] usePt; private double distanceTolerance; public DouglasPeuckerLineSimplifier(Coordinate[] pts) { this.pts = pts; } /** * Sets the distance tolerance for the simplification. * All vertices in the simplified linestring will be within this * distance of the original linestring. * * @param distanceTolerance the approximation tolerance to use */ public void setDistanceTolerance(double distanceTolerance) { this.distanceTolerance = distanceTolerance; } public Coordinate[] simplify() { usePt = new boolean[pts.length]; for (int i = 0; i < pts.length; i++) { usePt[i] = true; } simplifySection(0, pts.length - 1); CoordinateList coordList = new CoordinateList(); for (int i = 0; i < pts.length; i++) { if (usePt[i]) coordList.add(new Coordinate(pts[i])); } return coordList.toCoordinateArray(); } private LineSegment seg = new LineSegment(); private void simplifySection(int i, int j) { if((i+1) == j) { return; } seg.p0 = pts[i]; seg.p1 = pts[j]; double maxDistance = -1.0; int maxIndex = i; for (int k = i + 1; k < j; k++) { double distance = seg.distance(pts[k]); if (distance > maxDistance) { maxDistance = distance; maxIndex = k; } } if (maxDistance <= distanceTolerance) { for(int k = i + 1; k < j; k++) { usePt[k] = false; } } else { simplifySection(i, maxIndex); simplifySection(maxIndex, j); } } }