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Date: Sun, 27 Dec 2015 18:10:05 +0100
From: "Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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Subject: Re: [geda-user] Re: DRC clearance work in progress
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> "Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via
> geda-user AT delorie DOT com]" <geda-user AT delorie DOT com> writes:
> 
> >> "Peter Clifton (petercjclifton AT googlemail DOT com) [via
> >> geda-user AT delorie DOT com]" <geda-user AT delorie DOT com> writes:
> >> 
> >> > Focus on within-layer clearances for now.
> >> >
> >> > Any more complex design rules (such as dielectric breakdown through
> >> > the layer stack) requires more data than we have in PCB's data-model,
> >> > and may actually belong in a separate calculation utility that would
> >> > calculate out a geometric design rule that can be applied in PCB.
> >> 
> >> I am playing with the idea to build a DRC tool that works on the gerber
> >> output, using libgerbv and the clipper library (C++)
> >> 
> >>  http://angusj.com/delphi/clipper.php
> >> 
> >> I have made Python bindings for importing gerbers into clipper polygon
> >> data structures, perform bloating/shrinking and clipping operations.
> >> 
> >> Design rules would be specified as boolean operations on suitably bloated
> >> layer data, and anything left in the end is a violation.
> >> 
> >> An example that I have working now:
> >> 
> >>  from pyclipper import Clipper, gerbv, OffsetPolygons
> >>  proj = gerbv.project()
> >>  proj.load("v01.front.gbr")
> >>  proj.load("v01.plated-drill.cnc")
> >>  scale=10000
> >>  raw     = proj[0].polygons(scale)
> >>  drill   = proj[1].polygons(scale)
> >>  clip = Clipper()
> >>  clip.clear() 
> >>  clip.addsubject(raw)
> >>  # clean up, and remove keyholes
> >>  routing = OffsetPolygons(clip.union(),1)
> >>  # require 12 mil annuklar rings
> >>  annular = OffsetPolygons(drill, 120)
> >>  clip.clear()
> >>  clip.addsubject(annular)
> >>  clip.addclip(routing)
> >>  annular = clip.difference()
> >> 
> >> Any polygon left in annular is a violation.
> >> 
> >> For net specific rules I'd need to add some input that gives for each
> >> net at least one coordinate (per relevant layer).  And some code to find
> >> the polygon at the given coordinate.  Some rules, like clearance checks,
> >> require iterations over the individual ploygons in a layer.  At that
> >> point they could be tagged with a netname by the given coordinates.  And
> >> then there could be overrides of bloat values for specifiv nets.
> >> 
> >> I plot the ploygons with gnuplot right now.  A gerber export may be
> >> usefull to visualize the violations in gerbv.  Or some gui.
> >
> > Great!
> >
> > I think your work will would be useful within pcb to.
> >
> > Simple scale will give a little bit to large distance value in outer
> > corner, attached picture, there need to be a circle segment but it
> > could be fixed later at any point and to large distance is usually
> > less of a problem than to small distance.
> 
> Currently my Python bindings only support circle segments, but the
> Clipper library can do other corner handling as well :-)

Actually a full circle with clearance distance radius should work fine for all corners.