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Waguespack c01.tex V2 - 08/30/2008 1:44pm Page 19
UNDERSTANDING SOLIDS VS. SURFACE MODELING 19
the history tree and retrace their steps toward the beginning of the part creation process, selecting
the point to rebuild the rest of the model. Unfortunately, with history-based modeling, anything
that was previously created from that point forward would be deleted and have to be re-created.
The current generation of solid modelers provides dynamic feature-based parametric model-
ing, where powerful features can be added, modified, suppressed, deleted, or reordered within
the model without having to re-create good geometry. With the introduction of feature-based
modeling, 3D became a must-have within the engineering community. Now, complex designs can
be quickly created and modified to create virtual prototypes of complex machines without having
to cut metal to prove the design.
The following are frequent questions among 3D users: Which is better? Should I use surface or
solid modeling? Which should I use? The answer is that you should become proficient at using
both and never have to limit your abilities. Both surface and solid modeling have a place in today’s
engineering environment. Learning to use both proficiently should be on the agenda of every
aspiring modeler.
Although solid modeling is preferred by more users, primarily because it is a simpler approach
to design, the ability to add surfaces to sculpt or modify a solid model, or to add faces that would
be difficult to impossible to create using solid model features, adds a new dimension to creating a
quality model. It’s one of the little things that differentiate an expert user from the rest of the pack.
Let’s look at definitions of some of the aspects of solid and surface modeling:
Wireframe A collection of curves and lines and other geometry is connected into a 3D (XYZ)
construction representing the outer boundaries and features of a 3D part. See Figure 1.9 for an
example of a wireframe model.
Figure 1.9
Representation of a
wireframe type model
Surface A 3D mesh is composed of U and V directional wires or vectors representing a 3D
face. Surfaces are generally described by a few different types: polyface meshes (typical in graph-
ics modelers), representing planar faceted faces with joined edges culminating in one face;
triangulated meshes (typical in STL files), composed of three-sided planar faces connected into
one mesh; NURBS surfaces (based upon nonuniform rational B-splines), providing smooth, con-
stantly evolving surfaces that can be constrained and made tangent to other adjoining surfaces
and providing smooth surface transitions across a single part.
Inventor supports NURBS surface types in created or imported geometry. Figure 1.10 shows
an Inventor surface model, typically displayed as a translucent object. Surfaces can be com-
bined with solid models in a number of ways to enhance your modeling experience.