kicad-developers team mailing list archive

[jp charras <jp.charras@xxxxxxxxxx>]

Le 05/08/2015 19:41, Jean-Paul Louis a écrit :
> I do not understand why 6 significant digit will cause rounding error if Gerber generation uses inches as unit.
> you have a nanometer resolution which provides 6 decimals for millimeter units.
> When you divide this number by 25.4 to convert to inches, you might loose a bit of resolution, but you will not generate a rounding error.
> 123.456789mm = 4.86050350” wich is now 4.860503 when using only 6 decimals.
> 
> Where is the rounding error coming from? From the software processing gerber data? I really doubt that CAM software will care about 1 micro-inch error.
> 
> Just curious,
> 
> Jean-Paul
> AC9GH
> 

When rounding a coordinate, you slightly move corners of polygons.

1 micro-inch (25 pcbnew internal units) error has no matter for CAM
software (and users...) as long it does not create self intersecting
polygons.

If happens, an error report is made.
I am guessing this issue does not create actual problems (at least, when
happens, I did not see any issue with Gerber viewers I used).

But I already received bug reports about that issue.

And what is the reason a Gerber file needs inches ?
Currently I do not yet see the answer to my question.

I understand a Gerber reader (for instance Gerbview) has to accept a
Gerber file both in inches and mm (like all Gerber readers), but why
this is needed for Gerber file creation?

Moreover, there are many other parameters for Gerber coordinates notation.
First versions of Pcbnew have these options in plot dialog.
But because very few users are able to correctly choose these options,
they are now removed.

I never saw a board house which is unable to read Gerbers files in mm.
I cannot even imagine it could exist in 2015.
But if happens to me, be sure I will use an other board house.

-- 
Jean-Pierre CHARRAS