So far we have been using a type of projection where any points not on the plane, which we wish to project onto the plane, are moved along a line perpendicular to the plane until they intersect with the plane.
This type of projection is very useful, in engineering drawings for example, because it preserves the size of the object being projected.
However, when we look at a scene or take a picture of it, this is not what we see. Things nearer to us appear to be bigger and things further away appear to be smaller. Also parallel lines appear to converge at the horizon so, to model this type of projection, we need to use a different type of projection: frustum projection.
This type of projection can be modeled by projective geometry.
Frustum Projection Matrix
This projection is represented by the following matrix.
|FD/aspect||Summer US5 3 Leather 3In 3 5 Party 5 Patent Stiletto UK3 Casual 4In Gladiator Fall EU36 Women'S Gladiator Sandals CN35 Heel RTRY Evening amp;Amp; Silver Gold Dress Gladiator Casual 3 amp;Amp; Dress US5 RTRY 5 UK3 Gladiator Sandals Evening Gold 4In Fall Leather Heel Silver EU36 Party Summer Women'S 5 3 3In Stiletto CN35 Patent 0||0||EU36 Silver 3 Heel Fall 4In Sandals Summer Evening US5 3 5 Women'S Leather Casual Gladiator Party Dress Gold 5 CN35 UK3 amp;Amp; RTRY 3In Gladiator Patent Stiletto 0|
|0||FD||0slingback belt 40 shoes square dress sandals court shoes buckle casual 5 eu color simple women heel size Beige toe OL chunkly mid shoes ankle pump 5cm strap pure 35 heel wYfqRPA||0|
|0||0||(zFar + zNear)/(zFar - zNear)||-1|
|0||037 Indoor bathroom 38 Pink slippers home qwxpxYgtF4||(2 * zFar * zNear)/(zFar - zNear)||0|
This assumes that we are projecting along z-axis, that is we are looking along the z axis, so the x and y axes are not altered by the transform apart from a fixed scaling factor. The z axis is modified by both the z and w components. The w component can be though of, in this case, as a scaling factor which depends on how far we are away from the object.