kicad-developers team mailing list archive

[Wayne Stambaugh <stambaughw@xxxxxxxxxxx>]

On 10/17/2014 8:44 AM, jp charras wrote:
> Le 17/10/2014 14:22, Mark Roszko a écrit :
>> Alright, I've played around. It appears there is many CAM/gerber
>> software that cannot handle G75 arcs that are full 360 degrees. I
>> tested this with the board from Jon and the 1 pin test board from
>> Nick. If I generate 359 degree arcs, the 3d viewer is happy and draws
>> good circles. If I generate 360 degrees then the arcs disappear/screw
>> up.
>> As far as I can tell, the math is right for the arcs regardless of 360
>> or 359. I think it's because the start point == end point for a 360
>> degree arc, that some viewers may break down due to their graphics
>> libraries.
>>
>> I modified KiCAD to generate the circles as two arcs and the same
>> viewers seem happy.
>>
>> i.e. I made
>>
>> void GERBER_PLOTTER::Circle( const wxPoint& aCenter, int aDiameter,
>> FILL_T aFill,
>>                              int aWidth )
>> {
>>     Arc( aCenter, 0, 3600, aDiameter / 2, aFill, aWidth );
>> }
>>
>> into
>>
>> void GERBER_PLOTTER::Circle( const wxPoint& aCenter, int aDiameter,
>> FILL_T aFill,
>>                              int aWidth )
>> {
>>     Arc( aCenter, 0, 1800, aDiameter / 2, aFill, aWidth );
>>     Arc( aCenter, 1800, 3600, aDiameter / 2, aFill, aWidth );
>> }
>>
>> Many other CAD software also generate circles as multiple arcs instead
>> of a full g75.
>>
>> Attached are my generated gerbers, 360 won't work, but 270, 359 and
>> split arcs will work I believe.

Do we really want to be in the business of working around other peoples
broken software?  I really don't want KiCad to be part of that world.
It's one of the reasons I am willing to work on KiCad for free.  While I
appreciate your effort, this is something I would not commit unless we
are violating the gerber specification which appears not to be the case
if JP is correct.  What we should be doing is sending high quality bug
reports including references to the gerber specification, screen shots,
files that cause the problem, etc. so the developers of the various
broken gerber viewer apps and make it their responsibility to fix their
code.

> 
> OK.
> However, the Gerber specification says:
> "Under G75, if the start point of the arc is equal to the end point, the
> arc is a full circle of 360°"
> 
> See
> http://www.ucamco.com/files/downloads/file/81/the_gerber_file_format_specification.pdf?46dfe8d5c8aee229e773d81222fd4db4
> 
> page 55, chapter 4.4.6
>