/* * 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.noding.snapround; import java.util.*; import com.vividsolutions.jts.geom.*; import com.vividsolutions.jts.algorithm.*; import com.vividsolutions.jts.noding.*; /** * Uses Snap Rounding to compute a rounded, * fully noded arrangement from a set of {@link SegmentString}s. * Implements the Snap Rounding technique described in * the papers by Hobby, Guibas & Marimont, and Goodrich et al. * Snap Rounding assumes that all vertices lie on a uniform grid; * hence the precision model of the input must be fixed precision, * and all the input vertices must be rounded to that precision. * <p> * This implementation uses simple iteration over the line segments. * This is not the most efficient approach for large sets of segments. * <p> * This implementation appears to be fully robust using an integer precision model. * It will function with non-integer precision models, but the * results are not 100% guaranteed to be correctly noded. * * @version 1.7 */ public class SimpleSnapRounder implements Noder { private final PrecisionModel pm; private LineIntersector li; private final double scaleFactor; private Collection nodedSegStrings; public SimpleSnapRounder(PrecisionModel pm) { this.pm = pm; li = new RobustLineIntersector(); li.setPrecisionModel(pm); scaleFactor = pm.getScale(); } /** * @return a Collection of NodedSegmentStrings representing the substrings * */ public Collection getNodedSubstrings() { return NodedSegmentString.getNodedSubstrings(nodedSegStrings); } /** * @param inputSegmentStrings a Collection of NodedSegmentStrings */ public void computeNodes(Collection inputSegmentStrings) { this.nodedSegStrings = inputSegmentStrings; snapRound(inputSegmentStrings, li); // testing purposes only - remove in final version //checkCorrectness(inputSegmentStrings); } private void checkCorrectness(Collection inputSegmentStrings) { Collection resultSegStrings = NodedSegmentString.getNodedSubstrings(inputSegmentStrings); NodingValidator nv = new NodingValidator(resultSegStrings); try { nv.checkValid(); } catch (Exception ex) { ex.printStackTrace(); } } private void snapRound(Collection segStrings, LineIntersector li) { List intersections = findInteriorIntersections(segStrings, li); computeSnaps(segStrings, intersections); computeVertexSnaps(segStrings); } /** * Computes all interior intersections in the collection of {@link SegmentString}s, * and returns their {@link Coordinate}s. * * Does NOT node the segStrings. * * @return a list of Coordinates for the intersections */ private List findInteriorIntersections(Collection segStrings, LineIntersector li) { IntersectionFinderAdder intFinderAdder = new IntersectionFinderAdder(li); SinglePassNoder noder = new MCIndexNoder(); noder.setSegmentIntersector(intFinderAdder); noder.computeNodes(segStrings); return intFinderAdder.getInteriorIntersections(); } /** * Computes nodes introduced as a result of snapping segments to snap points (hot pixels) * @param li */ private void computeSnaps(Collection segStrings, Collection snapPts) { for (Iterator i0 = segStrings.iterator(); i0.hasNext(); ) { NodedSegmentString ss = (NodedSegmentString) i0.next(); computeSnaps(ss, snapPts); } } private void computeSnaps(NodedSegmentString ss, Collection snapPts) { for (Iterator it = snapPts.iterator(); it.hasNext(); ) { Coordinate snapPt = (Coordinate) it.next(); HotPixel hotPixel = new HotPixel(snapPt, scaleFactor, li); for (int i = 0; i < ss.size() - 1; i++) { hotPixel.addSnappedNode(ss, i); } } } /** * Computes nodes introduced as a result of * snapping segments to vertices of other segments * * @param edges the list of segment strings to snap together */ public void computeVertexSnaps(Collection edges) { for (Iterator i0 = edges.iterator(); i0.hasNext(); ) { NodedSegmentString edge0 = (NodedSegmentString) i0.next(); for (Iterator i1 = edges.iterator(); i1.hasNext(); ) { NodedSegmentString edge1 = (NodedSegmentString) i1.next(); computeVertexSnaps(edge0, edge1); } } } /** * Performs a brute-force comparison of every segment in each {@link SegmentString}. * This has n^2 performance. */ private void computeVertexSnaps(NodedSegmentString e0, NodedSegmentString e1) { Coordinate[] pts0 = e0.getCoordinates(); Coordinate[] pts1 = e1.getCoordinates(); for (int i0 = 0; i0 < pts0.length - 1; i0++) { HotPixel hotPixel = new HotPixel(pts0[i0], scaleFactor, li); for (int i1 = 0; i1 < pts1.length - 1; i1++) { // don't snap a vertex to itself if (e0 == e1) { if (i0 == i1) continue; } //System.out.println("trying " + pts0[i0] + " against " + pts1[i1] + pts1[i1 + 1]); boolean isNodeAdded = hotPixel.addSnappedNode(e1, i1); // if a node is created for a vertex, that vertex must be noded too if (isNodeAdded) { e0.addIntersection(pts0[i0], i0); } } } } }