“Sphere to Tangential Plane”: Polar (Normal) Aspect - Map Projections: Cartographic Information Systems - page 209

Fig. 5.15. Maximal extension of a normal central perspective of the sphere, the functions √ 1+ x and 1 / √ 1+ x ,
domain 0

≤ x ≤

5 ,x := 2 R/H

Fig. 5.16. Spherical vertical section, general normal perspective mapping of the sphere to the tangential plane
at the South Pole, projection plane at maximal distance