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Date: Tue, 22 Jul 2014 19:21:24 +0200
From: Gabriel Paubert <paubert AT iram DOT es>
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Subject: Re: [geda-user] Gerber Export Generates Abitrary Drill Tool Numbers
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On Tue, Jul 22, 2014 at 11:32:22AM -0400, Geoffrey Yerem - HEAT, LLC wrote:
> Hi,
> 
> >This said, it was also probably the weakest of my arguments. You simply
> >can't mixup Gerber photoplotter files and Excellon drill files, therefore
> >independent number spaces should never cause a problem.
> 
> I imagine that in the worst case that you could add a check box to
> the gerber dialog that enables an independent number space ("start
> Excellon drill count from one") for the Excellon files.

This is really overkill, this unified number space was introduced
with a rewrite of the Gerber exporter around 2008 (from looking at 
the archives of the drill files I produced) and I consider that it 
was a mistake to unify drill and apertures number spaces (that's
why I submitted the patch to separate them, I use it on all
my boards right now).

A long time ago, Gerber exporter used overlapping number spaces
for all Gerber files (a given aperture had the same number on all
layers), while now the Gerber files use disjoint aperture spaces.
Actually I already suggested that we should give the option of
3 possible aperture allocation policies:
1) start at D10 (or D11) on each layer
2) use a global aperture space (like old PCB versions)
3) use disjoints aperture spaces (like now)

I think that 2 should be the default, especially if we switch
to flashed apertures. The problem with 3 is that it can create
an enormous number of apertures for no real good reason. Current
limit of the Gerber specification is ~2^31 but it was 999 until
recently. Option 1 could be used if you really overflow the
999 limit with option 2, and option 2 is a reasonable compromise.

	Gabriel