Chapter 30: Using Imported Geometry and Direct Editing Techniques
and drivers to display curvy shapes. Mesh data is used by Hollywood and video game computer
graphics studios, and NURBS data is used by engineering and manufacturing companies. It is easy
to convert NURBS to mesh, but more difficult to convert mesh to NURBS. The mesh to NURBS
conversion can be done, but complex software and specialized expertise is needed for it to happen
correctly.Note
SolidWorks can make the mesh to NURBS conversion with the Scan To 3D software that is part of the
Premium package. Because this is not included in the Standard package, it is beyond the scope of this book and
will not be covered here. n
Understanding the Traditional Role
of Direct Edit Tools
What I call “direct editing” is also known by other names. You may hear it referred to as direct
modeling explicit modeling, or history-free modeling. I call it direct editing because the way the
geometry is created is all approximately the same and the difference is in the way edits are made.
In fact, one of the claims to fame of direct editing software tools is that it is the only system
that deals effectively with imported geometry, because “geometry is geometry,” regardless of its
source — native or imported. This is the reason why I cover imported geometry and direct edit
tools together in this chapter.Traditionally, direct editing CAD software has lived by the rule that how you create geometry should
not affect how you edit the geometry. Therefore, direct edit CAD packages still use functions like
extrude and revolve to build parts, but they would not return to those functions to edit the part; they
would instead directly manipulate faces of the part by moving, offsetting, and rotating.CAD software that depends on direct editing tools has existed for a long time: it has been around
longer than parametric history-based CAD software. In the last several years, some new direct edit
CAD products (Sketchup and Spaceclaim) have appeared on the scene and have renewed an inter-
est in direct edit techniques. Until this recent resurgence, the direct edit programs were seen as
old-fashioned and inferior to parametric history-based programs.Part of the charm of the direct edit scheme was that the software didn’t add any information to the
model. The model could be transferred between direct edit CAD packages without losing any
information. This is clearly not the case with parametric history-based CAD software, where you
basically lose the ability to edit the existing model when you transfer it from one parametric
history-based program to another. You can add new features, but you can’t change what originally
appears.