kicad-developers team mailing list archive

[jp charras <jp.charras@xxxxxxxxxx>]

Le 06/08/2015 08:39, Lorenzo Marcantonio a écrit :
> On Wed, 05 Aug 2015 16:56:02 +0200,
> Wayne Stambaugh wrote:
>>> There is a technical reason to not do inch plotting.
>>> I recently explained it.
> 
> Seems a pretty good reason, actually... sorry I don't ready every thread
> on the list.
> 
>>> Therefore, until someone give me a *very good reason* why inches are
>>> better than mm in Gerber files, I *do not want* a inch option in Gerber
>>> plot menu ( or, if this option exists, commit an algo to avoid self
>>> intersecting polygons).
> 
> Silly question: couldn't we raise the decimal figures on MOIN too, to
> avoid the problem or is it already at the max?

It is currently the max (6 digits max both in inches and mm), unless I
missed something.
6 digits for mantissa is the value given as best value in Gerber file
format spec.

 Or maybe the rounding
> creep is of that kind that couldn't by fixed by brute force but only
> using 'correctly directed' rounding (i.e. point on the left rounded up,
> point on right rounded down or something like that).

Yes, an algo is needed to modify corners coordinates.
The tests are not easy.

I remember difficulties when I had to debug such an issue in a Gerber
file, just to see if a corner was on the left or on the right of a
outline segment.

The best way (from the point of view on Gerber format) is to use a
representation not sensible to rounding coordinates (namely a polygon
with no hole linked to the main outline, and holes given as negative
objects).

(See last gerber file format spec, chapters 4.6.10 to 4.6.14)


> 
> Just curious, I don't actually expect that someone could reject a MOMM
> gerber file... (OTOH I know people which would reject a metric gencad
> file :(
> 

Gencad always creates issues: I saw data mandatory with a gencad reader,
and not accepted by an other reader.

-- 
Jean-Pierre CHARRAS