**Subject:** [Boost-bugs] [Boost C++ Libraries] #13566: difference and intersection yield wrong result

**From:** Boost C++ Libraries (*noreply_at_[hidden]*)

**Date:** 2018-05-16 06:51:43

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#13566: difference and intersection yield wrong result

--------------------------------------+----------------------------

Reporter: Henrik Zimmer <henrik@â€¦> | Owner: Barend Gehrels

Type: Bugs | Status: new

Milestone: To Be Determined | Component: geometry

Version: Boost 1.66.0 | Severity: Showstopper

Keywords: |

--------------------------------------+----------------------------

We are developing new algorithm that will hopefully be based on

boost::geometry. Unfortunately we have come across some errors in the

difference and intersection computations (possibly related to #13522 and

#13553), which are a central part of the algorithm.

I posted my original problem as a comment in #13522

(https://wandbox.org/permlink/ThHHAW13DOdHbgEx)

After reading #13553 I tried out the define BOOST_GEOMETRY_NO_ROBUSTNESS

which at first seemed to work. However, I then ran into a problem at

another position (https://wandbox.org/permlink/8YH8EiIRMtsUd1LH)

The two polygons have finite, not too small intersection, but both the

intersection and the difference are empty.

The problem seems be that the two geometries overlap almost exactly in one

vertex (0.0054, -0.02436) - this is the second vertex of the green polygon

and the first vertex of the blue polygon.

Changing the coordinate (0.0054) in the green polygon only slightly yields

the correct result.

-- Ticket URL: <https://svn.boost.org/trac10/ticket/13566> Boost C++ Libraries <http://www.boost.org/> Boost provides free peer-reviewed portable C++ source libraries.

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