Vanishing point of multipoint perspective, and historian Kirsti Andersen compiled these observations. She notes, in terms of projective geometry, the vanishing point is the image of the point at infinity associated with , as the sightline from through the vanishing point is parallel to . As a vanishing point originates in a line, so a vanishing line originates in a plane that is not parallel to the picture . Given the eye point , and the plane parallel to and lying on , then the vanishing line of is . For example, when is the ground plane and is the horizon plane,
Vanishing point then the vanishing line of is the horizon line . Anderson notes, "Only one particular vanishing line occurs, often referred to as the "horizon". To put it simply, the vanishing line of some plane, say , is obtained by the intersection of the image plane with another plane, say , parallel to the plane of interest (), passing through the camera center. For different sets of lines parallel to this plane , their respective vanishing points will lie on this vanishing line. The horizon line is a theoretical line that represents the eye level of the observer. If the object