fixed at the origin. R is the projected point.</para>

- <para>What we have are two similar right triangles; the triangle formed by E, R and

- E<subscript>z</subscript>the origin; and the triangle formed by E, P, and

+ <para>What we have are two similar right triangles: the triangle formed by E, R and

+ E<subscript>z</subscript>, and the triangle formed by E, P, and

P<subscript>z</subscript>. We have the eye position and the position of the

unprojected point. To find the location of R, we simply do this:</para>

<para>Thus, we define a new space called <glossterm>camera space.</glossterm> This is

not a space that OpenGL recognizes; it is purely an arbitrary user construction.

However, it can be useful to define a particular camera space based on what we know

- of clip space. This minimizes the differences between camera space and a perspective

- form of clip space, and it can simplify our perspective projection logic.</para>

+ of our perspective projection. This minimizes the differences between camera space

+ and the perspective form of clip space, and it can simplify our perspective

+ projection logic.</para>

<para>The volume of camera space will range from positive infinity to negative infinity

in all directions. Positive X extends right, positive Y extends up, and positive Z

is <emphasis>forward</emphasis>. The last one is a change from clip space, where