[Boost-bugs] [Boost C++ Libraries] #13636: distance calculation can be wrong for rings with collinear segments

Subject: [Boost-bugs] [Boost C++ Libraries] #13636: distance calculation can be wrong for rings with collinear segments
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2018-07-17 12:49:55

#13636: distance calculation can be wrong for rings with collinear segments
-------------------------------------------------+-------------------------
 Reporter:  stfn <p1433025@…>                    |      Owner:  Barend
                                                 |  Gehrels
     Type:  Bugs                                 |     Status:  new
Milestone:  To Be Determined                     |  Component:  geometry
  Version:  Boost 1.67.0                         |   Severity:  Problem
 Keywords:  distance ring collinear pythagoras   |
  segment                                        |
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 While unit-testing our code using boost::geometry, I stumbled upon a weird
 distance calculation: For two rings that are perfect 2d boxes and share
 the orientation and one segment length, their distance is calculated as
 zero although they are clearly not intersecting:

 https://wandbox.org/permlink/Z9DMLo52IdhZRCFb

 I made a rough sketch of the situation:
 https://www.desmos.com/calculator/7jbmeu9jqq.

 ----

 Note the line

 {{{
 // slightly change the values
 vehicleRing[2] = Point2D(vehicleRing[2].x() + 1e-10, vehicleRing[2].y() +
 1e-10);
 }}}

 .. changing vehicleRing[0] or vehicleRing[1] also results in zero
 distance, whereas slightly moving vehicleRing[2] results in the expected
 distance.

 ----

 Sorry for being lazy and not finding a simpler test-case (resp. simpler
 numbers), I just copied the values I generated in my own testing pipeline.

-- 
Ticket URL: <https://svn.boost.org/trac10/ticket/13636>
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