Re: gEDA-user: General Layers questions

[Martin Kupec <martin.kupec@xxxxxxxxx>]

On Wed, Mar 16, 2011 at 10:36:24AM -0600, John Doty wrote:
> 
> On Mar 16, 2011, at 4:24 AM, Stephan Boettcher wrote:
> 
> >> Ok. So "via" should be a circle element on "hole" typed layer.
> > 
> > No.  A Via is a composit, consisting of a circle on the hole layer, and
> > various circles on copper layers, and circles on mask layes, and
> > thermals.
> 
> The "layer" concept should be physical, not a metaphysical abstraction. Objects in a layer may contain holes, but a "hole layer" is nonsensical, a toxic conceptual shortcut. An "outline" layer is similarly bad: the insulating layers may all have the same shape sometimes, but not always.

The outline layer will be part of 'physical' layer. So if you have 2
'physical' layers with different shape, it will play nicely.

What I am prosposing is 2 level concept. There will be 'physical'
layers, so you can add properties to them. And than there will be
'drawing' surfaces. And 'outline' is just drawing suface telling the
'physical' layer it's edges.

But I am not convinced that we need special 'hole' typed layer. Maybe we
can things like 'holes' which are not part of any specific layer just
float in space. I thing that it would work.
> 
> Trying to model things that aren't layers as if they were layers is one common mistake in this kind of tool. Equally common is leaving out layers: the insulating layers in a PCB are just as important as the copper, and have their own properties (shape, thickness, material, etc.). They're a critical part of the layer stack.

The problem I see with the insulating layers is that there is nothing on
them...So you don't need them as 'drawing' layers. But I agree that
there should be a way how to add some attributes to them.
> 
> The description language needs to be able to express "feature p in layer x is aligned with feature q in layer y" in order to build up composites. This is the geometrically sensible way to describe the result of drilling through several layers. But the geometric description language should not be tied to any particular fabrication procedure.

I agree with this one.



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