[cad-linux] Re: the parametric project


--- Thomas Schmidt <thomas.schmidt@xxxxxxxxxx> wrote:
> 
> Roland,
> 
> It seems you actually want to setup a new parametric modeller. The
> brave =
> ones rule the world.

:-) That really hits the nail on the head - I am glad you said the
"brave ones" allthough I am sure you thought of 's/brave/crazy/' here. 

Anyway, such a modelling kernel would be some really interesting
project, especially if it is backed up by a database as was discussed
earlier. 

A CAD system that allows a user to specify dimensions by parameters is
probably built upon some form of a constraint solver. I assume that the
term "parametric" is used  because what the user actually notices and
sees is, that an edge can have a length that can be changed at any time
and the endpoints will automagically move. Parametric is a term that
refers to the application of the solver not it's implementation. 

The first and most succesful system that implemented this feature was
certainly Pro-E, they even named the company Parametric. 

Roland



> I assume that you use the term "parametric"  not to refer to the
> parametr=
> ic functions of curves and surfaces,
> but to a system, where objects interact by constraints. I have ever
> wonde=
> red why the term "parametric"
> is used to describe a constaint solving system. Does anybody know?
> Anyway, you might want to have a look here :
> http://www.cs.washington.edu=
> /research/constraints/
> The constaint solver they describe, are mostly based on local
> propagation=
>  algorithms
> and therefor not very well suited for (complex) 3D modelling, but you
> get=
>  a good introduction into the world of
> constaints and their solving algorithms. There is even some code for
> a fe=
> w solver.
> I also found many research papers about constaint solving algorithm
> on ht=
> tp://citeseer.nj.nec.com/cs.
> Search for constaints or solver. Mostly academic papers, but
> interesting =
> anyway.
> 


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