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 12:58 -0800, Ben Jackson wrote:
> On Tue, Feb 17, 2009 at 08:02:42PM +0000, Peter Clifton wrote:
> > 
> > I think the first hint of trouble is exemplified by PCB's failure to
> > clear this the 360 degree arc from the polygon. I've distilled a
> > test-case from your example (attached).
> 
> Yes, as soon as he said it I figured that the self-intersecting arc would
> blow up.
> 
> > I wonder if (as a workaround) you'd get better results from two
> > half-arcs, rather than one arc which touches its-self.
> 
> If it were a line PCB would meld it, but it might work for an arc.  On
> the other hand, coincident lines (which normally would have been merged
> but were not for some reason) have caused other clearing problems.
> 
> I think the only straightforward way to fix the self-intersecting arc is
> to build it internally from two parts and union them.  Might be slow on
> teardrop'd boards.

Probably just need some simple geometry to work out if it would
self-intersect or not fn(radius, width, angle), and do something
different with those cases which do. Unfortunately, there is (of
course), a whole family of potential intersections, so its not quite as
simple as just specifying an outer circle poly, with a circular hole.

Since this probably isn't a common case, I'd not have a problem in
requiring the performance hit for it.

Ben, did you figure out what specifically causes co-incident lines to
cause grief? My understanding of the code was that they shouldn't cause
problems. (I'd love to see any simple test-cases you have where they
do).

As you may have noticed, I've done a bit of hacking on the polygon code
recently. Not specifically in the contour intersection routines (yet),
rather in the contour gathering.


-- 
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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