Accuray issue with geometry::difference() in version Boost 1.57 (and 1.58)

[mikkel.stegmann@…]

I'm having an accuracy issue with geometry::difference() in Boost v1.57 (and v1.58) that I didn't see with v1.55. The test program is listed below. I compiled using g++ 4.4.7 on Ubuntu 12.04.

Result using Boost v1.55:

         249.232           761.09
         249.232           760.98
          265.89           760.98
          265.89          729.219
          94.021          729.219
          94.021           761.09
         249.232           761.09

Result using Boost v1.57 (and v1.58):

249.232003466816           761.09
         249.232           760.98
          265.89 760.979984987659
          265.89          729.219
          94.021          729.219
          94.021           761.09
249.232003466816           761.09

Apparently, it is related to the rescaling policy introduced in v1.56. I can mitigate the issue by defining the BOOST_GEOMETRY_NO_ROBUSTNESS.

Best regards,

Mikkel B. Stegmann

---

#include <boost/foreach.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry.hpp>

#include <cstdio>
#include <assert.h>

int main() {

  // 2D point with double precision
  typedef boost::geometry::model::d2::point_xy<double> BoostPoint;

  // 2D polygon, ring type: clockwise, closed ("the first point must be spatially equal to the last point")
  typedef boost::geometry::model::polygon<BoostPoint> BoostPolygon;

  BoostPolygon rectangleA;
  rectangleA.outer().push_back(BoostPoint( 94.021, 729.219)); // clock-wise points
  rectangleA.outer().push_back(BoostPoint( 94.021, 761.090));
  rectangleA.outer().push_back(BoostPoint(265.890, 761.090));
  rectangleA.outer().push_back(BoostPoint(265.890, 729.219));
  rectangleA.outer().push_back(BoostPoint( 94.021, 729.219)); // close

  BoostPolygon rectangleB;
  rectangleB.outer().push_back(BoostPoint(249.232, 760.980)); // clock-wise points
  rectangleB.outer().push_back(BoostPoint(249.232, 780.980));
  rectangleB.outer().push_back(BoostPoint(319.232, 780.980));
  rectangleB.outer().push_back(BoostPoint(319.232, 760.980));
  rectangleB.outer().push_back(BoostPoint(249.232, 760.980)); // close

  std::list<BoostPolygon> differencePolygons;
  boost::geometry::difference(rectangleA, rectangleB, differencePolygons);
  assert(differencePolygons.size()==1);

  BOOST_FOREACH(const BoostPoint &point, differencePolygons.front().outer()) {
    printf("%16.15g %16.15g\n", point.x(), point.y());
  }

  return 0;
}