src/operation/overlay/validate/OffsetPointGenerator.cpp

   1 /**********************************************************************
   2  *
   3  * GEOS - Geometry Engine Open Source
   4  * http://geos.osgeo.org
   5  *
   6  * Copyright (C) 2006 Refractions Research Inc.
   7  *
   8  * This is free software; you can redistribute and/or modify it under
   9  * the terms of the GNU Lesser General Public Licence as published
  10  * by the Free Software Foundation.
  11  * See the COPYING file for more information.
  12  *
  13  ***********************************************************************
  14  *
  15  * Last port: operation/overlay/validate/OffsetPointGenerator.java rev. 1.1 (JTS-1.10)
  16  *
  17  **********************************************************************/
  18
  19 #include <geos/operation/overlay/validate/OffsetPointGenerator.h>
  20 #include <geos/geom/Geometry.h>
  21 #include <geos/geom/LineString.h>
  22 #include <geos/geom/MultiPoint.h>
  23 #include <geos/geom/CoordinateSequence.h>
  24 #include <geos/geom/GeometryFactory.h>
  25 #include <geos/geom/util/LinearComponentExtracter.h>
  26
  27 #include <cassert>
  28 #include <functional>
  29 #include <vector>
  30 #include <memory> // for auto_ptr
  31 #include <cmath>
  32 #include <algorithm> // std::for_each
  33
  34 #ifndef GEOS_DEBUG
  35 #define GEOS_DEBUG 0
  36 #endif
  37
  38 using namespace std;
  39 using namespace geos::geom;
  40 using namespace geos::algorithm;
  41
  42 namespace geos {
  43 namespace operation { // geos.operation
  44 namespace overlay { // geos.operation.overlay
  45 namespace validate { // geos.operation.overlay.validate
  46
  47 /*public*/
  48 OffsetPointGenerator::OffsetPointGenerator(const geom::Geometry& geom,
  49                 double offset)
  50         :
  51         g(geom),
  52         offsetDistance(offset)
  53 {
  54 }
  55
  56 /*public*/
  57 std::auto_ptr< std::vector<geom::Coordinate> >
  58 OffsetPointGenerator::getPoints()
  59 {
  60         assert (offsetPts.get() == NULL);
  61         offsetPts.reset(new vector<Coordinate>());
  62
  63         vector<const LineString*> lines;
  64         geos::geom::util::LinearComponentExtracter::getLines(g, lines);
  65         for_each(lines.begin(), lines.end(),
  66                 bind1st(mem_fun(&OffsetPointGenerator::extractPoints), this));
  67
  68         return offsetPts;
  69 }
  70
  71 /*private*/
  72 void
  73 OffsetPointGenerator::extractPoints(const LineString* line)
  74 {
  75         const CoordinateSequence& pts = *(line->getCoordinatesRO());
  76         assert(pts.size() > 1 );
  77
  78         for (size_t i=0, n=pts.size()-1; i<n; ++i)
  79         {
  80                 computeOffsets(pts[i], pts[i + 1]);
  81         }
  82 }
  83
  84 /*private*/
  85 void
  86 OffsetPointGenerator::computeOffsets(const Coordinate& p0,
  87                 const Coordinate& p1)
  88 {
  89         double dx = p1.x - p0.x;
  90         double dy = p1.y - p0.y;
  91         double len = sqrt(dx * dx + dy * dy);
  92
  93         // u is the vector that is the length of the offset,
  94         // in the direction of the segment
  95         double ux = offsetDistance * dx / len;
  96         double uy = offsetDistance * dy / len;
  97
  98         double midX = (p1.x + p0.x) / 2;
  99         double midY = (p1.y + p0.y) / 2;
 100
 101         Coordinate offsetLeft(midX - uy, midY + ux);
 102         Coordinate offsetRight(midX + uy, midY - ux);
 103
 104         offsetPts->push_back(offsetLeft);
 105         offsetPts->push_back(offsetRight);
 106 }
 107
 108 } // namespace geos.operation.overlay.validate
 109 } // namespace geos.operation.overlay
 110 } // namespace geos.operation
 111 } // namespace geos
 112