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Date: Sun, 13 Sep 2015 23:04:46 +0200
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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On Sun, 13 Sep 2015 13:31:57 -0600
John Doty <jpd AT noqsi DOT com> wrote:

> 
> On Sep 13, 2015, at 12:24 PM, DJ Delorie <dj AT delorie DOT com> wrote:
> 
> > 
> >> If you do this right, you wind up with *exact* knowledge of every
> >> point in the x/y Cartesian geometry. Sines and cosines of these
> >> angles are rational numbers. No roundoff error. You can choose any
> >> unit basis you want (I'd go with meters).
> > 
> > I thought of this for arcs - define the endpoints and the radius, not
> > the center and angles (there are other issues in this example, but
> > still).  You're limited to what snaps to your grid, but if your grid
> > is nanometers that's a very small error.
> > 
> > You do tend to go off-angle pretty quickly though, since so many
> > angles result in irrational numbers.
> > 
> 
> What I meant to say is that the rational number solution is gridless. It has a base unit, but you can have coordinates like 45634/1299709.

It actually sound good if it could be implemented with a reasonable effort in practice.