409
Chapter 17
Cool Concepts
410 3D Animation for the Raw Beginner Using Maya
1: Four Coordinate Systems and Hierarchically Structured Models
2: 3D Surface Models—Components of vector-based models and pixel-based renderings
3: 3D Surface Models—Diagramatically
4: Manipulating 3D Models with Translate, Rotate, and Scale
5: Modeling—Approaches to modeling and adding detailed geometry
6: Modeling—Polygons, sculpting, and small granularity tools
7: Modeling—NURBS and its unique qualities
8: Putting Surfaces on Objects—Materials, textures, paint, and hair and fur
9: Putting Surfaces on Objects—Using textures
10: Animating 3D Models—Morphing and skeletons
11: Animating 3D Models—Physics in the large and in the small
12: Rendering and Lights—From vector to raster geometry, and the interplay of lights and materials in rendering
13: Rendering and Lights—e process of rendering, controlling the render process, and leveraging the visual artifacts of rendering
14: Creating a Scene—e big picture
15: Creating a Scene—For the novice
Cool Concepts 411
Cool Concept 2: What is a model?
Within Maya, there is a semiformal notion of an object—It can be something that will
render, like a car windshield, or something that does not directly render, like a path along
Models are in the eye of the animator. Often, the root of an object hierarchy is what the
animator considers to be a model.
4 Coordinate
Sy
stems and
Hi
erarchically
St
ructured
Mo
dels
Terms:
World Space (x, y, z):
Its center is at (0, 0, 0) of the scene
space.
Object Space (x, y, z):
a given object. Its center is at
Local Space (x, y, z):
Each object in the hierarchy
inherits the Object Space of its
parent (as its Local Space). In this
way, a complex object will move as
a coherent whole.
Surface Texture Space (u, v):
the surface of a given object.
Cool Concept 1: Object hierarchies and multiple (x, y, z) spaces
One of the most critical things a 3D animator must do is carefully place all objects in
appropriate hierarchical relationships with other objects. is allows the motion of one
object to depend on another object. is is how an object can be moved independently
but also be certain to move with respect to its parent. Building hierarchies also provides a
convenient way to place different materials on different parts of an object.
A Closer Look: Examples of using multiple (x, y, z) spaces
Consider a car on a roadway with various Objects hierarchically arranged.
Each axle has its own Object Space; its Local Space is the Object Space of the body of the car.
Now, the wheels turn independently, but they stay on the axle as the car moves forward. When a sinkhole
creating hierarchical movement. If we make the windshield of the car a child of the body of the car, it will
be easier to give the windshield its own material. It will also make it easier to reuse that windshield on
opens under the road, the road falls and the car follows, and the axles and the wheels go with it. e wheels
are still spinning.
412 3D Animation for the Raw Beginner Using Maya
A Closer Look: Why both straight and
curved line geometry?
Straight line geometry is quick to
manipulate, but often the animator uses curved
lines to specify particularly “organic” models.
its somewhat simpler cousin Bezier curves) is
surprisingly compact and reasonably quick to
mathematics that we use to represent Bezier
and NURBS curves. With only a few vertices and
some polynomials, a curve can be perfectly
3D Surface ModelsComponents of Vector-Based Models
an
d Pixel-Based Renderings
Terms: Polygons
wireframe” of a “polygon” object
contains “vertices” and straight edges
that connect the vertices in the World
Space of (x, y, z). But all edges are in 2-
space.
polygon faces
Straight edges form polygons, which
are calledfaces,” each of which is in
2-space.
A group of faces” form a “mesh.” One or
more meshes form a polygon object.”
Cool Concept 2: Vertices/edges/faces are converted to pixels
Although a polygon model is represented with line geometry in 3-space, ultimately
it will be rendered as pixels in 2-space, with each pixel having color and transpar-
ency attributes. Before it is rendered, each quad is cut into two triangles.
A NURBS model goes through an extra step: it must be turned into
a polygon model before it is rendered.
Terms: NURBS
wireframe” of a NURBSobject containscontrol verticesand “curves
In the World Space of (x, y, z). All curves are in 2- space.
curves
beginning and the end vertices are on the curve. But the other CVs are not; they are
CVs is actually a straight line.
patches
A NURBS object is a set of connected “patches.”
I

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