union_ fails to create holes

[jan.kleemann@…]

When uniting 2 polygons union_ does not create holes when it can also express the resulting polygon as a single ring, even if that ring has self-tangencies, which makes the polygon invalid.

The following code

typedef double FloatType;
typedef model::d2::point_xy<FloatType> Point;
typedef model::polygon<Point> Polygon;
typedef model::multi_polygon<Polygon> MultiPolygon;
typedef model::ring<Point> Ring;
typedef model::box<Point> Box;
typedef model::linestring<Point> LineString;


int main(int argc, char *argv[])
{
   using namespace std;

   Polygon p1, p2;
   boost::geometry::read_wkt("POLYGON((0 0, 0 1, 3 1, 3 0, 0 0))", p1);
   boost::geometry::read_wkt("POLYGON((0 1, 0 3, 3 3, 3 1, 2 2, 1 2 , 1 1, 0 1))", p2);

   boost::geometry::correct(p1);
   boost::geometry::correct(p2);

   MultiPolygon p3;
   boost::geometry::union_(p1, p2, p3);
   boost::geometry::correct(p3);

   cout << "p1: " << boost::geometry::wkt(p1) << endl;
   cout << "p2: " << boost::geometry::wkt(p2) << endl;
   cout << "p3: " << boost::geometry::wkt(p3) << endl;

   cout << "is_simple(p1): " << boost::geometry::is_simple(p1) << endl;
   cout << "is_simple(p2): " << boost::geometry::is_simple(p2) << endl;
   cout << "is_simple(p3): " << boost::geometry::is_simple(p3) << endl;
   cout << "is_valid(p1): " << boost::geometry::is_valid(p1) << endl;
   cout << "is_valid(p2): " << boost::geometry::is_valid(p2) << endl;
   cout << "is_valid(p3): " << boost::geometry::is_valid(p3) << endl;
   return 0;
}

has the output

p1: POLYGON((0 0,0 1,3 1,3 0,0 0))
p2: POLYGON((0 1,0 3,3 3,3 1,2 2,1 2,1 1,0 1))
p3: MULTIPOLYGON(((0 1,0 3,3 3,3 1,2 2,1 2,1 1,3 1,3 0,0 0,0 1)))
is_simple(p1): 1
is_simple(p2): 1
is_simple(p3): 1
is_valid(p1): 1
is_valid(p2): 1
is_valid(p3): 0

but p3 should be

MULTIPOLYGON(((0 1,0 3,3 3,3 0,0 0,0 1),(3 1,2 2,1 2,1 1,3 1)))

[jan.kleemann@…]

difference has the same problem:

p1: POLYGON((0 0,0 3,3 3,3 0,0 0))
p2: POLYGON((3 1,1 1,1 2,2 2,3 1))
is_valid(p1): 1
is_valid(p2): 1
p1 - p2: MULTIPOLYGON(((3 1,3 0,0 0,0 3,3 3,3 1,2 2,1 2,1 1,3 1)))
is_valid(p1 - p2): 0

Should also be

p1 - p2: MULTIPOLYGON(((0 1,0 3,3 3,3 0,0 0,0 1),(3 1,2 2,1 2,1 1,3 1)))

[Barend Gehrels]

Thanks for the report. It is fixed now in branch feature/cluster_touch. Hope to get it in 1.61

[jan.kleemann@…]

Nice! Thank you for your work.