Date: Sat, 4 Apr 2015 23:50:16 +0000 (UTC)
From: Cirilo Bernardo <cirilo_bernardo AT yahoo DOT com>
To: "geda-user AT delorie DOT com" <geda-user AT delorie DOT com>
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In-Reply-To: <1427552235.7680.22.camel@cam.ac.uk>
References: <1427552235 DOT 7680 DOT 22 DOT camel AT cam DOT ac DOT uk>
Subject: Re: [geda-user] 3D view
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My apologies for such a late reply; an overzealous spam
filter has been hiding things from me.

----- Original Message -----
> From: Peter Clifton <pcjc2 AT cam DOT ac DOT uk>
> To: geda-user AT delorie DOT com
> Cc: 
> Sent: Sunday, March 29, 2015 1:17 AM
> Subject: Re: [geda-user] 3D view
> 
>>  > I'd rather not put 3D models in the realm of pcb. An UI 
> infrastructure to 
>>  > design in 3D is far beyond the scope of a EDA layout application. But 
> even 
>>  > a good render engine is non trivial. These are tasks that are better 
>>  > relegated to 3D CAD applications and specialized render engines. 
>>  > 
>> 
>>  I agree; after all this is not the task of an EDA. For over 2 years 
> I've
>>  had some software to create parametric VRML models
>>  (http://kicad3dmodels.sourceforge.net) and since the models seem to get
>>  very little exposure and use I proposed to merge it with KiCad but was
>>  rejected.
> 
> Presumably is has a place in generating models which can then form part
> of the larger parts-library?
> 


Some volunteers are currently fixing things up for KiCad and my software
has been used to add over 150 new VRML models. However, many people are
more comfortable using a modeler like Wings3D since using this parametric
modeler would require learning either Python or C++.

> I just grabbed the code and had a very quick (30 seconds) skim. I had
> wondered how difficult it might be to translate to emit STEP, but I
> think we would have to know certain properties about the geometry were
> true (like avoiding self intersections), to do this without a solid
> modelling kernel. I don't see why we couldn't emit STEP surface geometry
> though, even if we don't go the whole way to solids.
> 
> In addition, the code was (obviously) designed to emit VRML, and not
> STEP, so whatever would require some work.
> 


I would (almost) completely rewrite the parametric modeler if I
wanted to output STEP; likewise if I would want to produce IGES.
However, it is possible to take the VRML output of this modeler
and generate IGES with no loss in data; however I would not recommend
that since (a) the representation would be extremely inefficient
and (b) a lot of VRML models will have surfaces which do not form
part of an object with non-0 volume so MCAD software will complain
endlessly about gaps in the model. I wouldn't even try to convert
VRML to STEP because edges and loops must be inferred and the end
result would be awful. However, I see no reason to create a
parametric modeler to emit STEP unless you want nicely colored models
rather than the usual gray ones in the wild. I think this dearth
of colored models will ensure KiCad's use of VRML well into the future;
I may rant a lot about VRML being nothing but eye-candy but it
gets some management types going 'ooh! aaah!' and it helps to sell
a project.

> Out of curiosity (and my laziness to figure this out for myself), how
> does KiCAD associate the transformation between a 3D model (granted, in
> VRML), and the footprint / package origin?
> 
> 
> Peter
> 


In KiCad the association is made by providing orientation and offset
data for each instance of the model. The export code is then responsible
for further transformations to position the model on the correct side of
the board and with the correct orientation. The transformations are
fairly trivial really; the VRML specification has a TRANSFORM entity so
the exporter only has to calculate the parameters to put into that
entity and doesn't have to deal with actually transforming all the
vertices (that's the task of the VRML viewer).

- Cirilo