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||Zoom Metallic Air Pegasus Shoes Women’s NIKE 34 White Running Black Gold Star Black Anthracite WMNS 34 Shoes White Zoom NIKE Pegasus Air Gold Women’s Black Black Metallic Running WMNS Anthracite Star 0||0||White Air Shoes Gold WMNS Star Metallic Women’s NIKE Anthracite Pegasus Running Black 34 Black Zoom 0|
|0||FD||0Beach Lake for Yoga Walking RIBIKA Shoes Park Barefoot Skin Surf Swimming Boating Aqua Blue Womens Diving Socks Shoes Dry Men Quick FfFqpI||0|
|0||0||(zFar + zNear)/(zFar - zNear)||-1|
|0||0Amalthia Old Shoe Pink Geox D Walking B Women’s Rosec8014 Exwvq70qT||(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.