On Mar 16, 2011, at 11:09 AM, Stephan Boettcher wrote: > John Doty <j...@noqsi.com> writes: >> >> 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. > > So, a via needs a separate hole in each copper and insulating layer? And > each layer needs its own discription of it's shape?
Just as a program needs to know that every object in an array of integers is an integer. The composition machinery is responsible for keeping track: you don't need to declare each array element separately. > >> 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 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. > > This is all too physikal for my taste. I assert that if you do it any other way, you wind up with the following catastrophe: the code for every layer type needs to incorporate a specific definition of its interaction with the code for every other layer type. A total collapse of factoring, poisoning flexibility and maintainability. But if layers correspond to actual geometric layers, this can be avoided, I believe. > > Why are you so attached to the concept of drilling? I'm not. Indeed, I would urge our developers to purge the idea that a hole implies a drill from their minds when considering geometry. Export to instructions for a specific fabrication technology is a different problem from geometry capture, and in well factored software these will be kept separate. > For the design of a > layout, all that matters is that there are conductive connections > between layers. At the netlist level, that's all that matters. But at the layout level, it's geometry that matters. John Doty Noqsi Aerospace, Ltd. http://www.noqsi.com/ j...@noqsi.com _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user