The vertical perspective projection is a map projection that corresponds to the appearance of a globe when directly viewed from some distance away with the -axis of the viewer aligned parallel to the positive -axis of the globe. It is given by the transformation equations
(1)
| |||
(2)
|
where is the distance of the point of perspective in units of sphere radii and
(3)
| |||
(4)
|
Note that points corresponding to are on the back side of the globe and so should be suppressed when making the projection.