Re: gEDA-user: neck-down example

[DJ Delorie <dj@xxxxxxxxxxx>]

> DJ does everything with arcs.  ;-)

I don't normally use them during manual layout, though.

> If you want a leg up on the math for this,

let a := width of thick line / 2
let b := width of thin line / 2
let r := distance from via center to thin line etch (radius + clearance)

Imagine a triangle that goes from the center of the via to the point
on the thin line perpendicular to the via to the endpoint for the
thick line.

The three legs of this triangle are:

r+a	(via to line ends)
r+b	(via to centerpoint)
c	(line ends to centerpoint)

Calculate c := sqrt ( (r+a)^2 - (r + b)^2 )

Calculate t = acos ( (r+b) / (r+a) )

So you need an arc of radius (r+b), thickness b, and angle t, and
switch from thick to thin line at c from the centerpoint.


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