Parallel Projection - viewing transformation

Parallel projection methods are utilized by engineers to make working drawings of an object that preserves its true shape. In the matter of parallel projection the rays from an object converge at infinity, not like the perspective projection, here the rays from an object converse at a finite distance termed as center of projection.

Parallel projection where all rays parallel occurs that is, when the distance of center of projection from the projection plane is infinity, then all rays from the object turn into parallel and will have a direction termed as "direction of projection", if the distance of center of projection from the projection plane is infinite. This is indicated by d= (d1,d2,d3), that implies d makes unequal or may equal angle along with the positive side of the x,y,z axes.