[cad-linux] Re: An open CAD file format
- From: Eric Wilhelm <ewilhelm@xxxxxxxxxxxxx>
- To: cad-linux@xxxxxxxxxxxxx
- Date: Sun, 7 Sep 2003 00:50:12 -0500
> The following was supposedly scribed by
> john kosty
> on Sunday 07 September 2003 12:33 am:
>ust identified the fatal flaw in wanting to adapt
>VRML: files are monolithic. This goes against the
>whole design concept. Disregard last... }-(
There is even more against VRML than that. Even if you can get over the
monolithic file, the data is so dirty and yet rather useless for anything
besides representation of the geometry (just a "pretty picture" as far as I
am concerned.)
The VRML spec is so flexible, that you can't write a program which will read
any compliant VRML file without allowing for every flexibility written into
the spec. If you haven't done a lot of programming, this won't be so easy to
appreciate. As a simplified explanation, consider writing if-statements
within if-statements inside a loop which is only activated if an enclosing
if-statement is satisfied (yes, that is the overly-simplified version:)
I have even found a GPL vrml viewer which utilizes a Perl library to load the
VRML into a data structure, but haven't yet been able to understand the data
structure (at least I haven't found it to be reliably any more predictable
than the VRML that it has had parsed into itself.) This is basically only
the first drawback to using VRML as an input format for modeling or
engineering data.
Now tell me how "triangle 72" knows that it is the left-front corner of the
sink and where we store the make and model (or even just density) of the sink
and tell me in a way that I can write a 30-line Perl script which pulls the
data for every sink installed in every project done in the last ten years so
that we can quickly and easily inform our clients that their sinks have been
found by the state of California to cause cancer in laboratory animals.
This is the sort of thing that should be possible with all of the data stored
in all of the dwg files and other cad-system-formats which are kicking around
out there somewhere. The issue is just how to get to it. I could write the
program to obtain this data about the sink from dwg files, but it wouldn't be
a 30-line script and it probably wouldn't even be as short as 3000 lines and
even then it would miss every project which wasn't done in AutoCAD or didn't
have a dwg file available on the search path for the final project drawings.
--Eric
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