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# Documents/Positioning/Tutorial 04.xml

`                         fixed at the origin. R is the projected point.</para>`
`                 </caption>`
`             </figure>`
`-            <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>`
`             <equation>`
`             <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`