Geometry Boost List: [ggl] Touching polygons and floating-point

Subject: [ggl] Touching polygons and floating-point
From: Barend Gehrels (barend)
Date: 2011-02-11 05:40:19

Op 11-2-2011 11:19, Denis Pesotsky schreef:
> Thanks for answer. But I mean a bit other thing. You noticied same
> thing in your blog ("Precision, the cause of spikes").
Sure.
> For example, 1st polygon have coordinates like (1, 1) and (4, 2.3)
> (and 1 more coordinate somewhere) and other have coordinates like
> (2.1, y1) and (3, y2), where y1 is y coordinate for crosspoint of
> Line({1, 1} {4, 2.3}) and y=2.1, while y2 is y coordinate for
> cross-point of same line and y=3. In float-point presentation that
> points can be not exactly on this line, but very close. Can this
> result in leaving 2 separate polygons after union?
>
In this described case, probably not, using float or double. But it 
might occur, yes. There is no fuzzy detection indeed. I'll come back to 
this with some details.

Barend