Chapter 7
The Structure of the Head and Features

Modeling a NURBS Head
UPDATED

Copyright 1999 Peter Ratner
(Excerpt from Mastering 3D Animation)

There are many approaches to modeling the human head. Most of these methods were designed to accomplish specific goals such as easier sculpting of facial features, better facial animation, easier texturing, and so on. Few of these modeling techniques have the scope to accomplish all the necessary goals that are necessary for a realistic head and its subsequent facial expressions.

Modeling a NURBS Head

One of the better methods for modeling a NURBS or spline head is to use vertical curves that begin on the inside of the mouth. These radiate outward to follow the contours of the features and finally end at the base of the neck (Figure 7-1).



Figure 7-1 The curves that define the facial features generally follow the direction of the muscles.

This approach works very well for creating a single mesh head that defines most of the features. Since the curves normally follow the direction of the muscles, it simplifies the task of animating expressions. This is especially true around the mouth which compared to the other parts of the face has the most movement. Before starting to model the face, it is recommended that one studies the various muscles and their purpose. While reading about these muscles, you may want to use a hand held mirror to observe their effects on various expressions


The Muscles of the Head



It is important to note that no muscle acts on its own. When one muscle contracts or draws together its fibers, it activates other opposing muscles which in turn modify the action of the original contracting muscle. Normally, the head is broken up into three sets of muscles. Most of these are small, thin or deeply embedded in fatty tissue. A few of the muscles shown in Figure 7-2 warrant special attention. They play an important role in facial expressions and help define the contours of the face.


Figure 7-2 The muscles of the head are divided into three groups. These are the scalp, face and mastication.



The Masseter and the Temporalis control the movements of the jaw. These muscles are responsible for the closing and biting movements of the mandible. The muscles which open the jaw are deep-seated inside the neck and are not readily visible.

The Frontalis is a broad flat muscle located in the forehead. It wrinkles the brow horizontally and raises the eyebrows. It contributes to an angry or surprised look.

Circling the mouth is the Orbicularis Oris. This elliptical muscle has the unique characteristic of not being attached to any bones. Instead, it is connected to a number of small muscles pointing toward the mouth. It curles and tightens the lips. The creases that result from contracting this muscle radiate from the lips and can often be seen in the elderly.

The Orbicularis Oculi is another circular muscle circumscribing the eye. Its contractions create wrinkles at the corners of the eyes (crow's feet). Its primary function is to close the eyelids for expressions such as squinting.

The Zygomatic Major angles from the side to the front of the face at the corner of the mouth. Its function is the energetic upward traction at the corners of the mouth. It takes fewer muscles to smile than it does to frown.

Located at the side of the nose are the three branches of the Quadratus Labii Superioris. Their function is to raise the upper lip for sneering.

The Triangularis and Depressor Labii Inferioris are responsible for the downward pull of the mouth and lips.

The Mentalis moves the skin of the chin and pushes up the lower lip.


Creating the Curves that Define the Head

One of the first steps that is highly recommended for accurate modeling is to load several image files of the front and side of the head. An image of the top of the head is also useful but not as important. Another approach is to use an existing model of a head and then shape the curves around it. Some head templates and models of heads can be found on the accompanying CD.

Beginning with the first curve, start drawing it from the inside of the mouth, curve it over the top lip, around the nose, forehead and skull and end at the base of the neck (Figure 7-3).



Figure 7-3 The first curve defines the profile and middle of the head. It starts on the inside of the mouth and ends at the base of the neck.