CG Basics - An Introduction to Computer Graphics for Artists - page 10

Fig. 2.1 ( Left ) Location of zero. ( Right ) A measurement based on zero

Fig. 2.2 2D and 3D Cartesian coordinate systems

where things are in relation to the origin point. This means that while the distance
from the origin to the Earth may be measured, the location of the Earth relative to
that point cannot be known. For this, some kind of system is required to establish
direction relative to the origin.
The French philosopher and mathematician Rene Descartes solved this problem
in the seventeenth century by describing what is now called a Cartesian coordinate
system. Cartesian coordinates defi ne the origin of any measurement as the intersec-
tion of two or three perpendicular planes. The linear intersection of these planes is
called an axis. Each axis is labeled with a letter to designate its direction. 2D coordi-
nate systems use the letters X and Y. 3D coordinate systems use the letters X, Y, and
Z (Fig. 2.2 ). To locate a point in space, one must fi nd the distance from the origin in
each of the axes being used, depending on whether it is a 2D or 3D system. Because
it is possible to describe every point in space this way, the Cartesian coordinate
system makes it possible to locate objects in 3D space relative to each other. Without