Re: gEDA-user: GL pcb bugs and a question re the log/library window, gerber outline output

[Peter Clifton <pcjc2@xxxxxxxxx>]

On Tue, 2009-02-17 at 13:29 -0800, Ben Jackson wrote:
> On Tue, Feb 17, 2009 at 09:08:33PM +0000, Peter Clifton wrote:

> It usually boils down to numerical instability in the polygon code.
> I may have an example.  I save all the strange boards people send in with
> bug reports to use as regression tests.

If that is due to the "snap rounding" problem, then the code _ought_ to
avoid it. If it is real instability, then presumably we'd end up having
trouble with cases other than coincident lines. (The line caps on the
end of two lines have a higher order of symmetry than the line
its-self).

I always have difficulty distilling simple test-cases on polygon
problems. Once some combination of geometry conspires to break one of
the invariants PCB's polygon code expects to hold true, all hell breaks
loose, and it can be hard to track down which piece of geometry was the
first aggressor. I probably have some of my own boards saved which cause
various printf / failures, but it is very hard to bisect the board to
get a single failing case.

Self-intersecting contours probably aren't a well-tested case, I'd
guess.



-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)



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