[Figure 24] The Transform and Shape Nodes in the Outliner.

Transform and Shape Nodes
In Maya, the transform node is the overall control modifying the object as a whole. The shape node is directly under the transform node and describes the form or shape of the geometry (NURBS, Polygons, and so on).

Hierarchy
A hierarchy is a relationship of nodes to other nodes described in terms of parent, child, and sibling. In the Outliner, relationships are defined by line segments that connect the nodes. In Figure 25, you can see the relationships that are created in a simple hierarchy. Notice how a node can be a parent, a child, and a sibling.

• Parent. A parent is a node or object that controls one or more children. A parent can be a child of another parent.
• Child. A child is a node or object that is controlled by a parent. A child can also be a parent of other children.
• Sibling. A sibling is a child with the same parent as one or more children.

[Figure 25] The Outliner with a hierarchy labeled to illustrate the parent/child/sibling relationships.

Inheriting Transformations
By default, a child object will inherit what is done to its parent object, transforming along with it and maintaining the same spatial relationship. This is behavior is known as inheriting transformations. By inheriting the transformations of the parent, the child travels with the object without changing any of its own values. For example, if you have object A (parent) at 0,0,0 and B (child) at 0,0,0, and you translate object A to 1,1,1, object B will follow in 3D space, but will not have any change in its value. If you turn off the Inherits Transform option, B will go back to 0,0,0. It is no longer calculating its transformation relative to its parent.

Hierarchy is a simple concept to grasp, and with experience, you’ll begin to understand the importance it plays in the building of 3D characters. Hierarchies may be simple, but what makes them hold together is a little more complex. Let’s take a look at the Transformation Matrix next, and see its important function in the 3D environment.

The Transformation Matrix
A transformation matrix defines how to move objects from one coordinate space into another coordinate space. Matrices are a kind of mathematical object. The theory of matrices is complicated, and is probably more sophisticated than anything you learned in your high school math classes, but the practical application is relatively simple and straightforward. A transformation matrix is a square pattern of numbers, arranged in rows and columns and enclosed in brackets, used to calculate a node’s transformations. Usually matrices are composed of a particular size, such as 4 x 4 — the first number being rows, second number being columns.

Transformation matrices are based on an order of predefined evaluations. The matrix used in Maya to update your object is actually the result of 11 separate matrix evaluations (14, if you include the individual calculations of each rotation axis.) Each time you transform an object, you are asking the computer to construct the matrices and combine them to find transformation values for that object. In most cases, this happens instantly, but when a scene is large and cumbersome you’ll begin to notice a slowdown in the speed of your computer. If you have a lot of objects that need to be evaluated, you might have to wait quite a while for the computer to construct and combine the 11 separate transformation matrices for every object in the scene.