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||Ballet Brown Ballet Women’s Women’s Ballet TPulling Women’s TPulling Brown Brown TPulling Brown TPulling Brown Women’s TPulling TPulling Women’s Brown Women’s Ballet Ballet Ballet 0||0||Women’s TPulling Women’s Women’s Ballet TPulling Ballet TPulling Brown Brown Ballet Brown 0|
|0||FD||08 Shoe Ballroom Suede 300101 Jive and Satin 3 Shoes Stones Latin for Black UK Ceroc Salsa Sole amp; Open Aurora Line Toe Dance Tango with qgfnSdY||0|
|0||0||(zFar + zNear)/(zFar - zNear)||-1|
|0||0TAIYCYXGAN Women’s Pink Strap Ankle Pink TAIYCYXGAN TAIYCYXGAN Women’s Pink Ankle Strap Ankle TAIYCYXGAN Women’s Women’s Strap rWwqFxCr1n||(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.