In perspective projection (from 3D to 2D), objects behind the centre of projection are projected upside down and backward onto the view-plane. This is known as view confusion.
Vanishing point: Where all parallel points appear to meet is called vanishing point.
Perspective foreshortening: As we move from centre of projection size of object varies inversely with distance, this is known as perspective foreshortening.
Topological Distortion: A line segment joining a point lying in front of the viewer to a point in back of the viewer is projected to a broken line of infinite extent.This is known as topological distortion.