Re: gEDA-user: pcb, how to remove mm garbage (very short lines)?

[John Doty <jpd@xxxxxxxxx>]

On Nov 19, 2008, at 11:22 AM, Steve Meier wrote:

> The Pads ASCII format uses a base unit of 0.00000002624671916 inches
> which is 1.0333354 nM
>
> Converting it to metric causes an error of about 0.5 nM
>
> The PCB base unit is 0.00001 inches
>
> Converting it to metric causes an error of 19.7 nM
>
> All I can figure out about why pads uses that weird number is that
> multiplying it by 38100 converts the base unit to mills
>
> Multiplying it by 9678 converts the base to 10 microns with an error
> of .6 nM
>
>
> So making the base smaller will reduce error (no surprise) the  
> question
> is what is a tolerable error?

If you insist on no artifacts, it's zero.

If you round imperial units to the nearest 0.01 mil, you have no  
additional roundoff error if your fundamental unit is 1 nm, because  
0.01 mil is *exactly* (by definition) 254 nm.

It's much harder to go the other way with a humanly comprehensible  
rounding because of the factor of 127 in the definition of the inch.

2^32 nm is about 4.3 meters, large enough for any PCB I've ever seen.  
2^64 nm is about 0.12 astronomical unit ;-)

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

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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