Error in polygon set shrink

[Jakob Schou Jensen <jakob.schou.jensen@…>]

I have a case where shrinking a four vertex polygon (polygon set) gives a wrong result. The input vertices are

(4000, 0)
(2500, 500)
(0, 3000)
(0, 0)

This is shrunken by an amount of 1000. The result should be a triangle but it is not. See attached image where the input polygon is red and the result is green.

[Jakob Schou Jensen <jakob.schou.jensen@…>]

red=input, green=result (shrink by 1000)

[Jakob Schou Jensen <jakob.schou.jensen@…>]

I compile the attached code with:

clang++ -I <path to boost>/boost_1_55_0 -std=c++11 shrink.cpp

on mac osx maverics.

[Jakob Schou Jensen <jakob.schou.jensen@…>]

Correction: The attach example should not give a triangle as the shrink result - rather an empty result. However, reducing the shrink to 750 instead of should give a triangle but it produces a result similar to the attached image. Both cases are wrong (unless I am violating some input constraint that I am unaware of).

[Andrii Sydorchuk]

Hi Jakob,

Thank you for your report and the attached image. I am going to investigate the issue.

[Andrii Sydorchuk]

Jakob,

The resizing (bloat, shrink) operation implementation is seriously broken. This is a known issue and am going to mark this as duplicate of "Ticket #6063". There is no explicit timeline for the issue to be fixed at the moment.

[Jakob Schou Jensen <jakob.schou.jensen@…>]

If these functions are known to be "seriously broken" would it not be better to remove them? Or mention the issue in the documentation?

[Jakob Schou Jensen <jakob.schou.jensen@…>]

(by the way boost::polygon is extremely cool and amazing!)

[Andrii Sydorchuk]

Thanks!

[Andrii Sydorchuk]

I will update documentation accordingly.