The model shows that in the case of a perspective mapping of two planes (who can be revolved one onto the other) the uniting lines of corresponding points all go through one point, the centre of perspectivity. In the model the perspective mapping of a circle into an ellipse is represented.

The intersection line of both of the carrier planes of the circle and the ellipse is a fixed point line of the perspective collineation (collineation axis). Through rotating of one of the planes (transparent) about the collineation axis the circle and the ellipse can be brought into a coplanar position, where the perspectivity stays the same. Therefore, you can deduce the perspective collineation in a plane out of the collineation in space. That is determined by the centre of perspectivity, the collineation axis and a pair of points, whose connecting line (collineation ray) includes the centre.