Re: gEDA-user: pcb crooked traces

[DJ Delorie <dj@xxxxxxxxxxx>]

The root cause of the problem is that the grid setting is a floating
point number.  It has to be to reduce cumulative error in metric grid
points, but it cannot convert metric grids to our mil-based grid
exactly.

Example:

A metric grid might have a "grid" setting of 100.11.  A particular
trace between two grid points that *would* have been a perfect 45, and
up being (made-up example) between 100,400 (100.11,400.44) and 200,501
(200.22,500.55) because of conversion rounding.  The off-by-one error
is due to the inexact representation of our grid settings as well as
rounding artifacts when converting to integer units.

Solution:

The solution - in this case - is to switch to a small metric-based
core unit.  Then, at least, our "normal" grid settings will always be
a whole number of core units, instead of being some unrepresentable
fraction.


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