Opened 5 years ago

## #9804 new Bugs

# boost::geometry::intersection returns input polygon when the result should be empty.

Reported by: | Owned by: | Barend Gehrels | |
---|---|---|---|

Milestone: | To Be Determined | Component: | geometry |

Version: | Boost 1.55.0 | Severity: | Problem |

Keywords: | Cc: |

### Description

The result of an intersection is sometimes equal to one of the input polygons, when the result should be empty. For example:

typedef boost::geometry::model::d2::point_xy<double> Point; typedef boost::geometry::model::polygon<Point> Polygon; Polygon pg1; Polygon pg2; boost::geometry::model::multi_polygon<Polygon> result; boost::geometry::append(pg1, Point(-6.0, 3.2500000000000013)); boost::geometry::append(pg1, Point(-9.0, 3.2500000000000022)); boost::geometry::append(pg1, Point(-9.0, 6.5)); boost::geometry::append(pg1, Point(-6.0, 6.5)); boost::geometry::append(pg1, Point(-6.0, 3.2500000000000013)); boost::geometry::append(pg2, Point(-3.0, 0.0)); boost::geometry::append(pg2, Point(-6.0, 0.0)); boost::geometry::append(pg2, Point(-6.0, 3.2500000000000013)); boost::geometry::append(pg2, Point(-3.0, 3.2500000000000009)); boost::geometry::append(pg2, Point(-3.0, 0.0)); boost::geometry::intersection(pg1, pg2, result);

After the intersection, result contains a polygon equal to pg1. We're using boost 1.55 and also tried the rescale_to_integer branch, which gives the same results.

The problem seems to be with boost::geometry::within. We've previously had problems with within that we resolved by using a different strategy. Changing the strategy of the within calls in the function update_selection_map in select_rings.hpp makes intersection return the correct result for this case.

**Note:**See TracTickets for help on using tickets.