Re: gEDA-user: pick and place ?plugin?footprints.c? for

[Dave N6NZ <n6nz@xxxxxxxx>]

Dan McMahill wrote:
> Dave N6NZ wrote:
>> What are the barriers to other angles?
> 
> Think about a SOIC package for example.  It is fairly easy to decide 
> what quadrant pin #1 is and once you know that, you're done if you only 
> allow 90 degree steps.  Now suppose you allow 45 degree steps.  Pin 1 
> for a SO6 will be in a different 45 degree slice than pin 1 of a SO16 of 
> the same orientation.  If you want to support arbitrary rotations, you 
> now have to take more steps to estimate what the axis of the part is. 
> There could be some metrics like "look for rows of pins that fall on a 
> line" but that will clearly fail for something that has its pads/pins 
> distributed around a circle.

OK, I understand the algorithm now.

But... since most pads are strokes, wouldn't looking at the XY endpoints 
of any single pad give you the rotation of one axis?  This fails on 
precisely square pads, of course.  But on any SO or TQFP part, just 
looking at the end points of pin 1 will tell you rotation.

> 
> Still, the suggestion about letting a footprint optionally include this 
> information to deal with "problem" parts might be an option.

Yes, even as I suggested it I considered it a band-aid.  If PnP info can 
be computed reliably, it should be done automatically. But let's face 
it, in every footprint library there are some footprints that are 
"higher maintenance" than others.  With a manually entered fall-back 
clause for cases where automatic calculation fails you can at least get 
a decent output file.  When the software gets smart grep will find all 
the tweaked footprints in your library so can rip out the manual band-aid.

-dave

> 
> -Dan
> 
> 


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