Projection reference point and use of Projection reference

Question

What is Projection reference point and use of Projection reference point?

Answer 1

In Perspective projection, the lines of projection are not parallel. Instead, they all converge at a single point called Projection reference point.

In Perspective projection, the object positions are transformed to the view plane along these converged projection line and the projected view of an object is determined by calculating the intersection of the converged projection lines with the view plane.