Re: gEDA-user: arcs in pcb

[Mark Rages <markrages@xxxxxxxxx>]

On Fri, Jan 29, 2010 at 6:28 AM, Peter Clifton <pcjc2@xxxxxxxxx> wrote:
> On Thu, 2010-01-28 at 19:05 -0600, Mark Rages wrote:
>> On Thu, Jan 28, 2010 at 3:50 PM, DJ Delorie <dj@xxxxxxxxxxx> wrote:
>> >
>> >> I was afraid of that...
>> >
>> > :-)
>> >
>>
>> So I guess I need to change the Arc object to store the angles in
>> floating-point and bump the file format version.
>>
>> Any objections?  It looks like a fair amount of work, including the
>> dark and foreboding "puller.c".
>
> Last time we discussed this, there was some comment on what to use.
> Fixed point seems appropriate, since it retains precision most
> uniformly.
>

Ok, what precision do we need?  A reasonable value would be to have
the uncertainty of the largest radius arc to be equal to the precision
of linear measurements.

Assuming: largest arc is 24 inches, and the desired precision 1e-5 inches.

Then the precision of the smallest angle is (1e-5)/24 radians or
2.38*10-5 degrees.  To be safe, the new units should be millionths of
a degree, so one revolution is 360000000.  Sounds good?  Or a
double-precision floating-point would maintain more than sufficient
accuracy over the (0,360] range.

> Other alternatives included adding an additional arc representation,
> defined by end-points in the usual PCB coordinates, and a third
> parameter, either a radius, curvature or a third point on the arc. (for
> example).

These are all equivalent within their precisions, right?  I think I'll
stick with what we use now because dxflib seems to work this way
(except using the normal X-Y directions) and we've pretty much got the
geometry worked out for this.  No need to open a new can of worms.

Regards,
Mark
markrages@gmail
-- 
Mark Rages, Engineer
Midwest Telecine LLC
markrages@xxxxxxxxxxxxxxxxxxx


_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user