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Subject: [ggl] Clipping (i.e. intersection) issues, still.
From: Chris Browet (cbro)
Date: 2009-07-06 05:51:17

2009/7/6 Barend Gehrels <Barend.Gehrels_at_[hidden]>

> Hi list,
>> There is still polygon-box intersection isues, unfortunately (with SVN
>> revision 869, at least).
> It turned out that it is the direction. If polygons are directed
> counter-clockwise, the generated intersection is the outside of that polygon
> with the inside of the box. Which is theoretically correct by the
> conventions we made. But it is of course not the intention.
> OGC defines that all polygons are directed clockwise, holes (interior
> rings) counter-clockwise.
> Chris, can you live for the moment with solution 1)? It means to call
> "ggl::correct", meaning that you probably have to make a copy, or call that
> immediately after the user edits the polygon, or whatever is convenient?
> Otherwhise we could think about 5) which is also feasable in a limited
> time?
Solution 1) is perfectly ok for me even as a long-term solution. Due to the
relative complexity for me of making custom polygons, I'm already making a
copy, and, as a matter of fact, was "correct"-ing at some point, but removed
it because I had in my mind "correct" only checked that the polygon is
closed (and was unaware of the "clockwiseness" importance while

I would suggest emphasizing this topic in the documentation for preview 5,
including detailing a bit what the "correct" function does.

- Chris -
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