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Date: Tue, 10 Jul 2012 11:12:34 -0400
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Subject: Re: [geda-user] gerber export - outline layer
From: Nathan Stewart <therealnathanstewart AT gmail DOT com>
To: geda-user AT delorie DOT com
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> Again we see that the pcb terminology of "layer groups" containing
> one or more "layers" is biting someone.
>
> Unless you have a good reason to do otherwise, always put
> exactly one layer in each layer group.
>
> Let's all pretend that these concepts are called "layers" and
> "sublayers" to make it clear which is the fundamental one.  It has
> been proposed that we call them "board layers" and "drawing layers"
> or something like that, but I'm not really satisfied with that
> since it should be completely clear from the name which is the
> top-level entity.  Actually if we could use a word other than
> "layer" for these sublayers it would be best.  I know that graphics
> and drawing programs use "layer" in general but it causes confusion
> since PCBs already use this term in a very specific way.  What
> other word could replace "layer"?
>
> Anyway, I've found that the current "sublayers" (simply "layers" in
> current pcb terminology) are seldom useful, since you can't show or
> hide specific layers in a layer group, and there are no useful
> per-layer properties (except color) that can be set.  I thought it
> would be useful to help separate the ground flood polygons on the
> bottom of a 2-layer board from the ground traces, but the only real
> benefit is that you can assign a different display color to it.

I interpreted it as follows: 'Layer' is a conceptual layer  'Group' is
a physical layer

Thus my two layer board had two 'groups', but 6 or 8 layers. I see
that 'silk', 'solder mask', and 'rat lines' are global conceptual
layers which do not belong to any group, as they don't show up in the
group dialog.

When I export, I do get a correct by default bottom solder mask, but
there doesn't appear to be any way for me to actually make changes on
the bottom solder mask layer due to the current arrangement. Likewise
- I haven't figured out how to do bottom silk.  Rat lines probably
should be global. I think defaults for N layer boards should be
outline, layer N, top silk, top mask, bottom silk, bottom mask. I
think a 2 layer board startup default should probably be the default -
since that 1) probably fits 80% of the boards done with PCB, and 2) is
going to be less confusing to new users.

On Tue, Jul 10, 2012 at 9:22 AM, Colin D Bennett <colin AT gibibit DOT com> wrote: