By knowing the field of view (FOV) and the dimension
of the projection plane, we can calculate the angle between
subsequent rays and the distance between the player and
the projection plane. These steps are illustrated in Figure
11 (Many books define these last two values arbitarily, without
telling the reader where the values come from, here is the justification.)
FIGURE 11 Here is what we know: Here is what we can calculate (brush up on your Trigonometry if you don't understand, most of these are high school level math):
So now we know:

