Re: gEDA-user: STEP Format? [WAS: Re: PCB+GL+3D Packages??]

[kai-martin knaak <kmk@xxxxxxxxxxxxxxx>]

Peter Clifton wrote:

> stl (very nice)

IMHO, stl is a mesh only format. That is, everything is made of
triangles -- no squares, no circles, no real curvatures. There are
no macros, no loops, or repetitions. A decent pcb would make for
a pretty large stl file if all the vias and pin holes were to be
modeled realistically. Named objects are unknown to stl. This
renders stl a one way format for most construction purposes. 
Vital information like the diameter of holes or boolean operations
of solids cannot be included.
In original stl there is no way to give color or texture information.
 There are color extensions, though. Their color depth is confined to
15 bit. So shades tend to look like a zebra. 

Most of the above is true for vrml, too. Due to its ability to 
associate textures with surfaces, it may be the format of choice
for good looking pictures. For construction purpose, it is a dead,
though.


> iges (simple format, but I have no clue what the syntax is ;))

syntax description is supposed to be available here:
http://www.uspro.org/documents/IGES5-3_forDownload.pdf/view
My browser is unable to connect, though. 

This format is more CAD friendly in that it allows for cylindrical,
spherical and even spline defined surfaces. In addition, it knows 
about objects. Because of this, iges can capture the exact dimensions
of engineered parts. For most CAD applications there is still loss of
information on export. Surfaces are contained as is, not as rendered
by construction points.

Color is added by object. There is no way to attach textures to 
surfaces. So unfortunately, iges does not lend itself to efficient
production of eye candy


> STEP (_utterly_ evil format).

This standard is supposed to cover every aspect in production 
of every industrial product, dismantling and recycling included.
Even with thousands of pages, it can only scratch on the breadth
of this goal. Most CAD vendors seem to have gravitated to the
automotive subsection. In addition, step exports seem to limit 
itself to about the rage of features that iges can provide. That
is, a geometrical description of the surface.

The specification of the format is kept almost as a secret. I 
wasn't able to get a glimpse on it for free.

For 3D features in pcb, all of the above suffer from some kind 
of deficiency. 

---<)kaimartin(>---
-- 
Kai-Martin Knaak
Öffentlicher PGP-Schlüssel:
http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x6C0B9F53



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