One last thing about Booleans--they may cause an automatic optimization
of the affected faces, meaning that unnecessary faces are removed.
Although this is often desirable, in some cases it causes polygons to
become non-planar or other mesh troubles. Test render your Boolean
results to look for problems like this, and consider turning off the opti-
mization option and re-trying the Boolean if problems show up.
Editing Mesh
When you start to manipulate only portions of a given object, you've
entered the realm of sub-object operations or mesh editing. This section deals
with a variety of options for altering your models at this level.
You witnessed the use of vertex-level editing to adjust 2D shapes back in
Chapter 2, "Delving into Cyberspace." Well, sub-polygon operations such as
vertex-, edge-, and face-editing can also be employed on 3D objects. This
process of vertex-level adjustment is often called pulling points, and is very
useful for sculpting or refining objects, adding small integrated details, and
fixing glitches in the mesh.
Vertex Operations
The tools and techniques used for vertex-level work are similar to those
used for 2D shape editing: Vertices can be copied, moved, deleted, rotated,
twisted, and otherwise manipulated with other standard transforms and
operations. Of course, a few of these transforms can't be applied to a
single vertex--some work on only a group of two or more.
Naturally, doing vertex-level editing work is tougher with 3D objects,
because you have the added dimension of depth to contend with, and
because the greater number of vertices makes it easier to accidentally select
and manipulate the wrong ones.
3 D G
R A P H I C S
& A
N I M A T I O N
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Booleans sometimes fail, either because the computer is unable to deal with the
complexities of the operation, or because their positions create vertex overlaps
or other problems. If a Boolean fails, try adjusting the position of the operands
slightly. As a last resort, you may need to either simplify the operands or tessel-
late the faces on one or both operands.
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