Elliptic Plane

The real projective plane with elliptic metric where the distance between two points  and  is defined as the radian angle between the projection of the points on the surface of a sphere (which is tangent to the plane at a point ) from the antipode  of the tangent point.

REFERENCES:

Coxeter, H. S. M. Introduction to Geometry, 2nd ed. New York: Wiley, p. 94, 1969.