gEDA-dev: PCB - XY values of centrioid in BOM/DXF exproter (was gEDA-user: PCB Element for a Molex 71661-2068?)

[Peter Clifton]

On Thu, 2007-03-08 at 08:03 -0500, Dan McMahill wrote:
[snip]

> > IMO it would be a good practice to use the center of gravity as a
> > mark/insertion point for pcb footprints/3D models.
> 
> yes.

What do other packages with 3D modelling use for their models?

Do you really mean centre of gravity, or some kind of geometric centre?
(Thinking of modelling components with non-uniform material density).

I'd have expected to use some centroid in the plane of the PCB, and to
have the Z axis of the attach point on the component correspond to the
plane of the PCB it rests on.

Eg. SMDs would start at Z=0 and go upwards in Z the height of the
component.

A through-hole capacitor would have its base at just above Z=0
(clearance for lead expansion / contraction), have the cylinder
extending up with +ve Z, and leads protruding down with -ve Z. (assuming
we go so far as modelling leads).


-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)