Re: gEDA-user: pcb, mm rounding issue

[David Kuehling <dvdkhlng@xxxxxx>]

>>>>> "Stefan" == Stefan Salewski <mail@xxxxxxxxxxxx> writes:

> I have 0.5 mm grid size, 0.25 mm line width and 0.25 mm "Minimum
> copper spacing" in Preferences/Design Rule Checking.

> It was clear for me that this can cause problems -- indeed it does.
> Sometimes it is not possible to draw copper lines on adjoining grid
> points if Settings/Auto Enforce DRC cleararance in enabled.

I recently stumbled into a related problem.  Running the DRC after the
board was almost finished, it reported lots of errors for those corner
cases.  (0.15mm lines with 0.15mm minimum spacing).

I fixed it by manually reducing the DRC limits by one "epsilon"
(i.e. 1/100 mil) in my .pcb file, changing 'DRC[591...' to 'DRC[590...]'

Looking at the integer units internally used by PCB, it is obvious that
591 is slightly more than 0.15mm, while 590 is slightly less.  So maybe
that's the reason that exact 0.15mm spacing is just not achievable.

Of course, if PCB somehow hid thes rounding issues from the user, some
people (like me) would be much happier.

David
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