Surface v Solid

From: Jon Hunwick (Delcam  International PLC)
To: RP-ML
Date: Thursday, February 2, 1995
Subject: Surface v Solid
Terry Wohlers writes:
To which Andre' replied:
 > In fact, there are advantages in using a surface modeller because you don't
 > *need* to create a closed volume before using RP if you have a tool that can
 > do that for you.

While I agree that (most) solid modelers are easier to use than
surface modelers, there are two important facts to be born in mind.

1 - Surface modelers allow the designer **complete** freedom to design
the shape that is actually required. Solid modelers are better at
prismatic shapes, and anyone who has ever used one will not dispute
that. But if the shape is more 'natural' and has complex free-form
curved surfaces then **most** solid modelers will be unable to do the
job. Even more true is the fact that once a curved object has been
defined, only the better surface modelers (like DUCT [sorry]) will
allow subtle changes without completely re-working the part.

2 - Surface modelers (while being more difficult to drive) impose less
restrictions on the user as he/she does not have the burden of
ensuring a manifold object at all times. This allows more creative
freedom.

So it's really a 'horses for courses' argument. What users need to do
is decide on the priority - do they want simple, or do they want total
control? The way I see it, there is no point in having even the best
CAD system in the world if it can't make the shapes **you** want to
make.  

|Jon Hunwick