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Author(s): S. Welke
Abstract:
raphic projection of plane
algebraic curves onto the sphere
S.
Welke, 7n der
Spwelke@aol com
1 Introduction:
Stereographic projection is a conformal map from the x — y— plane to the
unit sphere S* C R^.
The geometric definition is:
Definition 1 Let P = (x, y, 0) be a point in the x — y— plane, let N =
(0, 0, 1) be the North Pole of the unit sphere in R^, and let lp be the unique
straight line lp through P and N .
The intersection with the unit sphere is
a point P' ^ N .
The correspondence p : P \ — > P* establishes a one-to-one
map p : R^ — > S*\{N} called Stereographic projection.
We frequently identify (x,y) £ R% with (x,y, 0) G R^.
Note that there is no
point P in the entire plane with p(P) = N.
Given a point P, the line lp is the set {(0,0,1) +t(x,y,-l) \t £ R} =
{(tx,ty,t — 1) \t G R}.
Because P' belongs to the unit sphere, its coor-
dinates satisfy the following quadratic equation: (tx)* -f (ty)* + (1 — t)* = 1
with ...
Pages: 8
Size: 791 kb
Paper DOI: 10.2495/IMS970631
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