Remark for Perspective projection - Transformation
A Perspective projection can have at most three Principle Vanishing points and at any rate one Principle vanishing point. To know the consequences of a perspective transformation, identify the figure.
The figure demonstrates the perspective transformation on z=0 plane of a specified line AB that is parallel to the z-axis. The A*B* is the projected line of the specified line AB in the z=0 plane. Assume here that a centre of projection be at (0,0,-d) on the z-axis. The Figure (A) demonstrates that the line A'B' intersects the z=0 plane at the similar point as the line AB. This also intersects the z-axis at z=+d. This means the perspective transformation has transformed the intersection point.