CAD -> STL

From: Terry Wohlers (Wohlers Associates)
To: RP-ML
Date: Wednesday, February 1, 1995
Subject: CAD -> STL
Jon Hunwick,
> Most people assume that it is **much** easier to generate STL data from solid
> models, as they contain all the necessary topological information to allow 

Generally, I believe it *is* much easier to generate "buildable" STL data from
solid models. 

The "ease" of creating an STL file with a CAD system is not the problem.  The
challenge can be the creation of a good model, and thus, a good STL file, ...
which means creating a closed, water-tight solid volume.  I learned long ago
that it's much easier to create a closed volume using a CAD solid modeler. 
Properly functioning solid modelers create closed volumes by default.  This is
why they are called "solid" modelers.  

I don't doubt that you can produce a good STL file with a surface modeler
because many have.  But it can be tedius, and you are more likely to
accidentally produce a model that does not represent a closed volume.  I would
not want any rp-ml subscribers to conclude from your message that surface
modelers are as intuitive as solid modelers for prototyping.   Anyone agree or
disagree? :)

Terry Wohlers
Wohlers Associates