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From: karl AT aspodata DOT se
To: geda-user AT delorie DOT com
Subject: Re: [geda-user] footprint conversions (was: Valve / nixie symbols)
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Comments: In-reply-to "Erich Heinzle (a1039181 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
   message dated "Tue, 08 Mar 2016 21:35:36 +1030."
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Erich Heinzle:
> the problem to solve next is how to render polygons (from Eagle footprints)
> and trapezoids (in kicad footprints) in the converted gEDA footprint.

Do you have examples as png/jpg or something ?

> I think I will have to build them with concentric chains of end to end
> pads.

If you accept roundings at the corners that would work, if you want
sharp corners !=90° && < 180°, then I'm at loss since pcb don't support
polygons in element files.

I think it's sane to require:
. closed polygon (first point connects with last point)
. no self-intersections
. no holes

One could have a chain of incr. thicker pads, starting with the
thinnest on the polygon perimeter and the thickest at the polygon
center - or
 one could fill the interiour first, and then fill the corners to some
minimun radius.

I guess it's more economical to fill the interiour first, but filling
the perimeter first gives you the same corner radius for all corners.

Using perimeter first and filling a square (for ease of modelling)
using a corner radius r, first line is 2*r thick. Using an overlap
of o, the next line will have thickness of 2*R, where
sqrt(2)*2*r - o + R = sqrt(2)*R # think going from corner to next line center
i.e. (sqrt(2)2r - o)/(sqrt(2) - 1) = R, or if o = f*r
next line with is 2R = (2sqrt(2) - f)/(sqrt(2) - 1) * 2*r or
R/r = k = (2sqrt(2) - f)/(sqrt(2) - 1), and if h = square height
then h/2 >= k^(n-1) * r, n = number of lines (pads)

soo, if h = 10mm, r = 0.3mm, o = 0.1; then we need 3 lines (pads)
around to fill the square (I think...).

Using center first, we put a circle in the center and then fill the 
corners to some limit.

I'd think I like perimeter first even tough there will be a lot
of overlapping pads along the edges.

> Luckily, not many eagle and kicad footprints use them. Once
> implemented, it will work for kicad and eagle sourced footprints.

If there only is a few of them, maybe it's feasable to manually make
new fp's for them.

Regards,
/Karl Hammar

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