----- Original Message -----
> From: Lorenzo Marcantonio <[email protected]>
> To: Kicad Developers <[email protected]>
> Cc:
> Sent: Sunday, May 5, 2013 10:29 PM
> Subject: [Kicad-developers] About MCAD integration
>
> People keep asking about this... at the moment DXF is the only useful
> way to export a board to a 3D mcad (then you estrude it 1,6mm, usually,
> but you don't have component boundaries and stuff).
>
> IDF3 *is* plausible to make, but does actually someone want it? In
> SolidWorks AFAIK you have to buy a special purpose module to import it
> (strange thing: while IDF3 is designed to go both ways, it seems that
> only the ECAD->MCAD route is used). IDF4 exists but AFAIK nobody uses it
> (like IPC356B!)
>
DXF is not really useful for this purpose.
IDF3 works both ways (ECAD->MCAD and MCAD->ECAD) but all tools I have seen will
rewrite an entire set of IDF3 files; I do not know of any software which makes
changes to the files as described in the specification. IDF3 also has so many
limitations; for example everything is an extruded footprint so you can't
describe finer details - this makes more work for the mechanical designer when
checking information such as panel cutouts for PCB mounted parts. In practice
I've taken IDF3 files and replaced critical components with adequate 3D MCAD
models; this isn't so bad in many (most?) cases, but I believe we can improve
that. :)
Despite its flaws, many people do use IDF3. The specification is extremely
simple so it's not too difficult to implement; however, someone has to put in
the time to create the footprints and manage them. This is a big job and it is
why I haven't put any effort into IDF3 export.
You're right about IDF4 - very few people seem to use it. In fact I don't know
if even SolidWorks 2013 supports it. On one side people seem to use IDF3; on
the other side (EADS and other huge companies) people seem to use PSI5 (like
STEP, you pay $$$ for the specification).
See below for my comments on STEP.
> General consensus is that STEP is the desiderable format (too bad IGES
> went out of popularity... it was freely documented and it's the
> precursor of STEP). However it's huge, no, bigger than huge, it's
> ISO-committee-designed. I have found this old message around, for more
> information:
>
Don't even think about implementing a STEP library; that's a job which would
take a large team many years. It is best for us to make use of existing tools
like OpenCascade, but I also suggest that MCAD support should be done by
external tools and we should not make KiCAD dependent on any specific MCAD. A
scheme I suggested last year should work OK and require minimal support in
KiCAD - basically a few more tags to point to 3D models, which is similar to
what is currently done for VRML. The 3D model associations will have to be
abstracted so that KiCAD can manage the associations without really caring
about the specifics of the 3D tool (MCAD, VRML, etc).
> https://www.email-lists.org/pipermail/freearchitecture/2006-May/000079.html
>
> The only STEP toolkit available for open source is the one in
> OpenCASCADE. The zipped tar is more than 110MB (it's a whole geometry
> engine for cad...), I feel it's a little big as a dependency :D It seems
> that freecad uses it.
>
> I tried to look inside a STEP file. It's quite readable actually, *if*
> you have the schema to cross reference with. Too bad you have to pay,
> a lot, for that. And extremely verbose; it's actually a dump of a graph
> database (a good idea for a cad format IMHO). Too bad that for
> describing a parallelepiped geometry the ST-Developer kit (commercial)
> uses no less than 215 object (*two hundred fifteen* objects). And that
> using the AP-203 (the entry level schema). I reordered and indented the
> thing, it's quite obvious what is going on. I'll try to add a hole in
> that box to see what infernal representation it spawns:D
>
> However it seems feasible to reverse engineer the format for generating
> at least something like the IDF3 representation: board shape and prisms
> for component shapes. Not exactly like having the 'perfect' model, but
> beats extruding the board profile from the dxf at least.
>
> Any ideas on this? IIRC there were some people interested in this kind
> of thing.
>
Ultimately STEP is probably the most supported format for exchanging 3D
information; however it is an inconvenient format to use within an MCAD due to
the memory consumption. My idea was to wait until FreeCAD supports assemblies,
then work on a tool to generate a FreeCAD assembly using the KiCAD pcb file
and the native MCAD definitions for each component. This way KiCAD is not tied
to any specific MCAD. The 3D effort can also be concentrated on native FreeCAD
descriptions and these should be much smaller files than STEP. People then
have the option of doing their own packaging designs with FreeCAD, but they can
also export the assembly to STEP so that people can use whatever MCAD they want
for the mechanical design. FreeCAD can also import STEP, so we can still make
use of the numerous STEP files of parts available on sites like RS and in fact
it should be possible to mix native and STEP models in a FreeCAD assembly.
Even if we supported MCAD via FreeCAD, I imagine some people will still want
IDF3 just because that's what their work requires; recently someone was asking
about IDF3 support on the user list because their company required IDF3 and a
STEP generated via VRML->STL->STEP was not acceptable.
For 3D MCAD models I wonder if it is good enough to just model the rough
volumes (for example, pins on a QFP would be 4 wide tabs on each side of the
package rather than individual pins) or if there is currently any need or
foreseeable future need for much better fine detail in the model. Obviously
with better detail the MCAD can produce better eye candy, but for all work that
I've done I can't imagine a use for the fine detail except where cutouts are
needed.
- Cirilo
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