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Subject: Re: [geometry] #8376: difference of non-closed polygons returns closed polygon
From: Volker Schöch (vschoech_at_[hidden])
Date: 2014-10-10 04:39:35

> I tried this example as well (see attached program and output).
> What I see is that the output has 18 points (I can see that from both the dsv printout of the geometry, as well as from bg::num_points). So the resulting multi-polygon is not closed, but when you output it through bg::wkt, it is shown as closed.

Thank you very much for double-checking! In the mean time I, too, found that things may not be what they appear to be, but I could not yet nail it. Apparently, not only wkt but also read_wkt mix up the closedness. I got caught by this because I have a number of unit tests in place based on read_wkt, which are now triggering like crazy.

I'm glad that it's just wkt/read_wkt, and not the actual algorithm, that is at fault.

Should I file a ticket for the wkt/read_wkt issue? It interferes with debugging, unit-testing, and with reporting issues, too!
Volker Schöch | vschoech_at_[hidden]
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