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.
Elliptic Plane
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References
Coxeter, H. S. M. Introduction to Geometry, 2nd ed. New York: Wiley, p. 94, 1969.Referenced on Wolfram|Alpha
Elliptic PlaneCite this as:
Weisstein, Eric W. "Elliptic Plane." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/EllipticPlane.html