CG Basics - An Introduction to Computer Graphics for Artists - page 9

Chapter 2
CG Basics

2.1 Introduction

Artists have long sought to craft convincing representations of three-dimensional
(3D) objects (Bauer 1987 ). To do this inside a computer, the computer must fi rst
be given information about the object. After the data is entered, the computer must
be told what to do with it to produce usable output. Normally, the output is an image
called a rendering . A rendering is like a photograph, except that the subject of the
image exists only as data stored in a computer, rather than as a material object
(Hagen and Bresnahan 1984 ). To understand CG, one must understand why certain
types of data are meaningful to a CG application, and how data is used to create the
results we see in video games, feature fi lms, TV advertisements, simulations, and
many other types of products.
This chapter is designed to introduce readers to how CG applications use the
data you give them to produce the results you want. It discusses the concept of
Cartesian space, polygonal geometry, textures, lighting, transformations, and ren-
dering. Chapters 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , and 15 cover each of these subjects in
greater detail.

2.2 World Space in CG

Imagine American astronaut Neil Armstrong when he fi rst landed on the moon.
Soon after this historic event, he ventured outside the moon lander and planted an
American fl ag in the dusty grey soil of the moon. Now imagine the intersection of
the fl agpole and the moon's surface as the center of the universe. In computer graphics,
this point is the world origin, and it would be the point against which every other
distance is measured (Fig. 2.1 ). With that point known, the distance from the world
origin to Armstrong's hand may be measured. However, although measurements
are made possible by a fi xed origin, the world origin is not suffi cient to determine