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Date: Sat, 23 Jan 2016 00:12:31 +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] PCB data structures
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Precedence: bulk

> >> > The PCB layout has an object of type pcb_layout as the root object, which can contain an arbitrary number of pcb_layer objects--which in turn contain the geometric primitives--and pcb_element objects which aren't associated with a layer.  Objects of type pcb_polygon can have child objects of type pcb_polygon_hole:
> >> >
> >> > pcb_layout
> >> > +- pcb_layer
> >> >    +- pcb_arc
> >> >    +- pcb_line
> >> >    +- pcb_pad
> >> >    +- pcb_pin
> >> >    +- pcb_polygon
> >> >       +- pcb_polygon_hole
> >> >    +- pcb_rat
> >> >    +- pcb_text
> >> >    +- pcb_via
> >> > +- pcb_element
> >> 
> >> Sounds reasonable, and similar to what we have now but with much cleaned up
> >> naming and hierarchy.
> >
> > I would say then looking at data layer by layer there are: arc, line,
> > circle, polygon and cutout of these drawing primitives.
> >
> > Pad/pin/via is a composite of these drawing primitives on different
> > layer, this is the case no matter how they are represented. 
> 
> I believe it is a mistake to have pcb_layer contain the drawing
> primitives.  A pcb_via or pcb_element shall contain the same drawing
> primitives, for any layers.  There may be a (hierarchy of) container(s)
> for drawing elements not contained in a pcb_via or pcb_element.  pcb_via
> and pcb_element shall be subclasses of such containers.

Sometimes it is useful with drawing primitives on layers for example then drawing lines on copper layer for connections. It is also useful to place footprint/elements on different layers, as is now top and up side down on bottom. For embedded components there would be a need to place footprints/elements on other copper layers facing up or down.

With a container I assume you mean something to collect objects. A footprint may for example have both drawing primitives on differenet layers and padstack containers for the pins/pads. As is now footprint/element container have lines and pads/pins but no padstack container.

> 
> > A hole is equal to a round cut out usually thru all board layers with
> > or without plating. Text is probably also a composite of other drawing
> > primitives.
> 
> A hole is a connection between layers.  No further assumptions about
> holes is needed before an export HID or a DRC ruleset is called.
> 
> -- 
> Stephan

A plated hole is a connection between layers but sometimes there is a need for other shapes than round and a cutout make sense for other kind of holes. As is today only possible cut out is a hole thru all layers with or without plating.


Nicklas Karlsson