Boost C++ Libraries: Ticket #10642: polygon_set_data bug with small coordinates

attachment set

lopresti@… — Thu, 09 Oct 2014 18:53:37 GMT

attachment → boostbug.cc

Small test case demonstrating bug in Boost.Polygon polygon_set_data

owner changed

Andrii Sydorchuk — Wed, 12 Nov 2014 22:06:52 GMT

owner changed from Lucanus Simonson to Andrii Sydorchuk

status, version changed; resolution set

Andrii Sydorchuk — Wed, 01 Apr 2015 01:41:07 GMT

status new → closed
version Boost 1.56.0 → Boost 1.58.0
resolution → fixed

Hi Patrick,

Thank you for your report. The issue was fixed as part of ticket #10976 . I added your example as another unittest. The fix was merged into master and develop branches and will be part of the Boost 1.58 release.

status changed; resolution deleted

Andrii Sydorchuk — Fri, 03 Apr 2015 22:47:27 GMT

status closed → reopened
resolution fixed

anonymous — Sat, 04 Apr 2015 16:40:59 GMT

Are you sure this is fixed in master? I ask because I just pulled a fresh copy from github and this test case still fails.

Also the patch adding the unit test (commit 3189de98d8299075d725bb59beb5c89cf53195e4) appears to have a typo... It reads:

BOOST_CHECK_EQUAL(32.0, area(polygon)); BOOST_CHECK_EQUAL(32.0, area(polygon));

I believe one of those should be "area(pset)" instead of "area(polygon)".

anonymous — Sat, 04 Apr 2015 16:43:58 GMT

Are you sure this is fixed in master? I ask because I just pulled a fresh copy from github and this test case still fails.

Also the patch adding the unit test (commit 3189de98d8299075d725bb59beb5c89cf53195e4) appears to have a typo... It reads:

BOOST_CHECK_EQUAL(32.0, area(polygon)); BOOST_CHECK_EQUAL(32.0, area(polygon));

I believe one of those should be "area(pset)" instead of "area(polygon)".

Andrii Sydorchuk — Sat, 04 Apr 2015 16:48:49 GMT

No, it's not fixed. That's why the ticket was reopened yesterday. I am going to do a deeper investigation of the issue this weekend.

Andrii Sydorchuk — Mon, 06 Apr 2015 21:16:10 GMT

The issue is related to the integer grid snapping logic the Polygon uses to handle boolean ops. Basically, any edge of the polygon that has another vertex of a polygon located within an integer 1x1 square has a chance to be broken into two separate edges at that point. That is what happens in this case. One way of fixing it, is to scale polygon to make sure that it doesn't have vertices and edges in 1x1 grid proximity. The best solution would be to fix snapping implementation, however this requires too many changes to the large legacy code base. Thus, I am skipping this option, being a single maintainer.

I am going to update the documentation that Polygon operations require sufficient proximity between polygon elements.