Inside region is not always on the left hand (parameter domain).

Cauchy Ding's picture
Cauchy Ding
Sun, 04/20/2025 - 11:06
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Modeling Data and Algorithms

Hi Guys,

I was taught in school that the inside region of the polygon is always on the left hand of the edge. But after tracing many cases from different .iges files in OCC, I find that's not true. I mean the algorithm in BRepTopAdaptor_FClass2d doesn't suppose the left hand theory. Is my observation right? If the left hand theory is not guaranteed in OCC, how does BRepTopAdaptor_FClass2d judge point inside/outside state?
Regards.

Ding

FYI: I've asked DeepSeek to analyze the code of BRepTopAdaptor_FClass2d. It always said the outer wire should be counter-clockwise (CCW), and the inner wire should be clockwise(CW). I guess it's wrong in OCC.