Stereographic projection
A stereographic projection is a projection from a sphere to a tangent plane. Stereographic projections preserve angles.
To stereographically project a point on a sphere to a plane tangent to its south pole, draw the line from the north pole of the sphere to the point in question. The stereographic projection of this point is then the intersection of this line with the plane. As such, the stereographic projection of the north pole will be undefined.
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