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Date: Thu, 26 Jun 2014 15:27:37 -0700
From: Cirilo Bernardo <cirilo_bernardo AT yahoo DOT com>
Subject: Re: [geda-user] pcb: Patch for arcs with different radii for x and y on screen
To: "geda-user AT delorie DOT com" <geda-user AT delorie DOT com>
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----- Original Message -----

> From: DJ Delorie <dj AT delorie DOT com>
> To: geda-user AT delorie DOT com
> Cc: 
> Sent: Friday, June 27, 2014 2:25 AM
> Subject: Re: [geda-user] pcb: Patch for arcs with different radii for x and y on screen
> 
> 
>>  Speaking of Gerber - at some point, we should re-validate our output
>>  choices against current UCAMCO recommended practice.
> 
> Note that UCAMCO says "standard gerber is obsolete" so we're going 
> to
> have a hard time following them...
> 


It's not a problem, when they say "standard Gerber" they mean the
original commands for driving the historic photo typsetting machine.
Some of that of course is now a subset of the 274-X specification
which is now on Revision J. Since Revision J has just been released
it will be some time before we see the new features exploited by
CAM software, but even when that happens you don't have to make use
of the newer features.

>>  I would suggest that we re-enable arc features in gerbers at some
>>  point,
> 
> We only interpolate non-circular arcs, which gerber simply doesn't
> 
> support.


Nor is Gerber ever likely to support non-circular arcs. The question
should be what types of arcs do you want to support and why?
I think circular arcs only makes the most sense since it is so simple.
If someone wants more interesting board edges or cutouts then it's
better to draw those in 2D CAD and use some tool to import the shapes,
possibly converting to straight segments. Even the elliptical arcs
aren't currently adequately supported - how do you control the rotation,
the arc angle, or the endpoints? What is the value of having elliptical
arcs?

- Cirilo