93
Chapter 4
Hierarchies of Objects, a Polygon
Example, Detailed Polygon
Modeling, and a NURBS Example
I
, we will continue to look at modeling. We take the approach of incre-
mentally digging more deeply into both polygon and NURBS modeling. Our goal is to
become comfortable with both, with a bit of a bias toward polygon modeling, as it is a core
3D technique with which every 3D artist needs to be familiar.
We rst examine a few semiformal and conceptual issues in Maya, then we build a
polygon model, take a high-level look at the process of creating another polygon model,
and study some techniques for performing various detailed polygon modeling tasks. And
nally, we look at constructing a NURBS model.
BASIC CONCEPTS
Modeling Hierarchies
We have been informally using the word model to refer to the goal of the 3D modeling
process. Of course, one must have a specic end point in mind. Although any complex
model (and many simple ones) will evolve during the process of creating it, you don’t want
to be making incidental models by continuing to semirandomly massage an object until it
nally looks like something interesting.
Perhaps a more critical notion is what gives a model its identity in the eyes of the mod-
eler. e quick answer is that it is at the root of an object hierarchy.
Objects
First, remember that the word object has a specic meaning inside Maya, and it refers to an
item stored in the Maya database. Objects can be things that are directly rendered or they
94 ◾ 3D Animation for the Raw Beginner Using Maya
can be abstract. In either case, they have attributes. Maya does, however, hide the specics
of its data management from us, and so it’s actually dicult to know precisely what is an
object and what is not.
We have also used the term object in a somewhat informal way to refer to pieces of a
model or early stages of a model.
Either way, models are made up of objects.
A model might be made of other models, as well. A model of a house might have smoke
coming out of the chimney, and that smoke eect might be a model that was made earlier
and then imported into the scene containing the house by going to File on the Main Menu
and selecting Import.
Formal Notions
e word model does not have a precise meaning in Maya, although we will continue to say
that a model is made of objects arranged in a hierarchy.
ere is a formal notion in Maya, though, of a project, as each project is a specic folder
in the Maya le directory. In this book, when we talk about scenes we will usually be refer-
ring to a specic .mb or .ma le within a Maya scenes folder, which is within the Projects
folder. So a scene is also a formal notion.
Maya binary les are encoded as bit les. Maya ASCII les consist of code. As an experi-
ment, you might try storing a scene as an ASCII le, and then look at the vast amount of
code that must be generated to create even
a simple model. is will give you a sense
of the astonishing amount of computational
power hidden inside Maya.
A .ma or a .mb le can be imported into
an open scene, and so our smoke eect
might be stored as its own .ma or .mb le.
We might reasonably conclude that a
scene is a precise thing that contains one or
more models, and that a model is made up
of objects.
Hierarchies
Remember the cactus we made from
NURBS curves. In Figure4.1, we choose:
any Main Menu → Window → Outliner
is window allows us to take various
objects in a scene, give them names, and
put them in a hierarchy. You can also give
objects names by using the Attribute Editor.
And of course, it is always a good idea to give
the objects in your scene meaningful names.
FIGURE 4.1 e Outliner.
Hierarchies of Objects, a Polygon Example, Detailed Polygon Modeling ◾ 95
In Figure4.2, the NURBS surfaces that we created have been renamed in the Outliner;
they are now called “trunk” and “branch.” e two NURBS spheres have been renamed
“trunkcap” and “branchcap.”
Notice that the curve we made with the EP tool is called curve1, which is not renamed.
e circles that were used for extrusion and for loing are not renamed either, although
perhaps they should have been. All of these objects started out at the same level in the
Outliner.
e trunkcap object has been selected and, using the middle mouse button (MMB),
dropped on top of the trunk object. is has put the cap underneath the trunk in the hier-
archy of objects that make up the cactus. Likewise, the cap of the branch has been MMB
dragged onto the branch, and the branch has been MMB dragged onto the trunk. is has
placed those objects in their positions in the hierarchy. Why use the Outliner to create a
hierarchy of objects? is is a critical concept in 3D modeling.
Doing this means that if we move the body of the cactus, the caps of the trunk and
branch will remain in place, and the branch will maintain its position with respect to the
trunk. In other words, if we translate the trunk in 3-space, the other objects will translate
in 3-space but strictly with respect to the location of the trunk.
In Figure4.3, only the trunk has been selected, but the entire cactus has been high-
lighted; this is because the objects now form a single hierarchy and will move as a unit if
the root, the trunk, is moved.
Models can be built out of objects or out of other models. To a nonanimator, the branch
of our cactus would probably not be viewed as an independent model, but we might want
to give it a name and look at it as a reusable component as we build a desert scene—and
so maybe it is a model as far as we are concerned. We would then make it a root of its
own hierarchy and make a copy of it every time we want to put a branch on a particular
cactus model.
FIGURE 4.2 Cactus hierarchy.
96 ◾ 3D Animation for the Raw Beginner Using Maya
If you make use of the Outliner in your
modeling, animating a scene will become
much easier, as objects will move appropri-
ately with respect to each other. It also helps
later if you want to reuse a model in a dier-
ent scene or project.
Another Example
If you look at Figures4.4, 4.5, and 4.6, you
can see that there is now some sorbet in our
glass dish. e sorbet should certainly stay
there when someone picks the dish up to
eat, so the sorbet is a child of the glass dish.
Both of these examples show why it is
so critical to rename things. In a complex
scene, you might have so many dierent
objects that it would be impossible to iden-
tify them later if you kept using the Maya
default names. Some people like to embed
the origins of a model or object in its name
so that they don’t start expecting it to act
like it was made in some other fashion.
FIGURE 4.4 Dish and sorbet.
FIGURE 4.3 e NURBS cactus.
FIGURE 4.5 Dish and sorbet Outliner selection.
Hierarchies of Objects, a Polygon Example, Detailed Polygon Modeling ◾ 97
So, our cactus trunk might be called
“trunk_NURBS_extrude.”
Extending the Notion of a Hierarchy
e Outliner actually keeps track of a
much larger notion of a hierarchy. If
you open the Outliner window and
select Show, and then select Objects,
you will see that everything else in
your scene sits in one hierarchy or
another. is includes lights, cam-
eras, and other objects that we have
not yet discussed, such as joints and
inverse kinematics (IK) handles (both
of which are used in skeletons to ani-
mate organic models).
You can select any object in your
Outliner window and it will be
highlighted in your scene. us, the
Outliner provides a quick way to
locate objects in your scene if you have
remembered to name them logically.
And, remember that what con-
stitutes a model is in the eye of the
beholder. e 3D artist uses the
Outliner to put together objects that
visually convey the model in the art-
ist’s mind. at hierarchy also facili-
tates the processes of putting materials
on the model and animating it.
The Importance of the Outliner
Later in this book, we will build a cow that
looks like a 2D (and not a 3D) model. In
Figure4.7, we see a preview of him. I have
put a cap on him. His cap moves along with
him as he walks because the cap has been
MMB dragged to the body of the cow in the
Outliner, making the cap inherit the move-
ment of the cow. e relevant fragment
from the Outliner is overlaid to the upper
right of the cow in the gure.
FIGURE 4.6 Dish and sorbet outliner.
FIGURE 4.7 A cow with a red and yellow hat.
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