Creating 3D Geometry - AutoCAD 2011 and AutoCAD LT 2011: No Experience Required - page 907

Most 3D models today utilize the solid-modeling tools for their basic shapes
because the tools for adding, subtracting, slicing, and so forth are easy to use
and allow complex shapes to be fabricated quickly. Still, mesh-modeling, legacy
tools retained from AutoCAD's initial foray into 3D, have their uses. Any serious
3D modeler will be familiar with both sets of tools.
using Surface-Modeling tools
New to this release is a third set of tools for creating even more complex forms
and shapes as surfaces. The surface-modeling tools share a number of similar-
ities with both the solid- and mesh-modeling tools already discussed. Surfaces
are like meshes in that they do not have a true volume; the cellophane wrapper
analogy also applies to surfaces. On the other hand, you'll notice a number of
tools appear on both the Solid and Surface Ribbon tabs.
Tools like Loft, Sweep, Extrude, and Revolve are found on both tabs, and they are
nearly identical in both contexts. The core difference between the two types is the
3D object created. When these tools are used from the Solid tab, they create solid
objects, with volume and mass. Using these same tools from the Surface tab will
create a skeleton object, a cellophane wrapper, with neither volume nor mass.
Figure 16.98 shows two boxes, each created using the Extrude tool. The box on
the left was created using the Extrude tool found on the Solid tab, and is a solid
box with a top, bottom, and sides. By comparison, the box on the right was created
using the Extrude tool found on the Surface tab. Notice how it lacks both a top
and a bottom, but each of its four sides is constructed with a number of smaller
rectangles. This grid structure is more easily manipulated into complex shapes,
something that's much harder to do using solid objects.
FiGuRE 16.98 Rectangles extruded with the Extrude tool on the Solid tab (left), and
the Extrude tool on the Surface tab (right)