Regression 1.78.0 - 1.79.0 (still in 1.82.0): difference of two polygons gives unexpected empty result

[gastald88]

I have two polygons p1 and p2, where the difference p1 - p2 is clearly non-empty (see image, p1 blue, p2 orange), but the difference operation returns an empty polygon.

Here below a godbolt link to replicate this problem:
https://godbolt.org/z/YTjM3GG1G

The result is correct in boost version 1.78.0 (you can set at the godbolt platform in the compiler arguments -I/opt/compiler-explorer/libs/boost_1_78_0)

From version 1.79.0 on (until the 1.82.0 that I recentely tested on my local environment) the result is incorrect.

I also tried to define the macro BOOST_GEOMETRY_ROBUSTNESS_ALTERNATIVE, but the bug is still there.

[vissarion]

Thanks for filing this issue.

I can reproduce your issue locally.

However, defining BOOST_GEOMETRY_ROBUSTNESS_ALTERNATIVE (before all includes) is working for me.
This seems to be one regression of rescaling removal in 1.79.

[gastald88]

Thanks for your answer,
I have wrongly put the macro definitions after all includes rather than before. Once fixed this, it worked as you said.
Thanks again!

[barendgehrels]

Fixed by commit eb879fe in PR #1193
It now also works without rescaling.
I will create a unit test and close the issue.

[barendgehrels]

Unit test in #1202