Re: [boost] Formal Review: Boost.Polygon starts today August 24, 2009

Subject: Re: [boost] Formal Review: Boost.Polygon starts today August 24, 2009
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-09-03 09:20:18

Simonson, Lucanus J wrote:
> John Phillips wrote:
> >    You have made variations of this assertion a few times in this
> > thread, and I wanted to point out one problem with it.
> >
> >    The distribution of the integers is not the same as the
> > distribution of the floating point numbers.
[snip]
> > So the user will be forced to choose between overflow errors
> > or lost precision.
>
> This is true, of course.  However, in such systems where
> large and small scales mix, floating point is itself
> problematic.  When snapping a large scale intersection point
> to the floating point grid it may cause a long edge to sweep
> arbitrarily far, potentially crossing to the other side of
> large numbers over vertices at a small scale near the
> floating point origin.  I would say that in general planar
> geometry has the property that precision of all points is
> equally important, and that floating point just provides the
> convenience of ignoring scale.  We mix large and small scale
> features in VLSI, our package layer looks like a PCB, while
> the metal layers below are many orders of magnitude smaller.
> If you can't represent the small features in your integer
> type because the extents of your large features are simply
> too huge you have many many many orders of magnitude
> difference between them, enough that by definition you won't
> be happy with floating point calculations either.

FAQ fodder?

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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