improper point, point at infinity, infinitely-distant point
A point that completes the plane in order to describe certain geometrical relations and systems. For example, an inversion is a one-to-one mapping of the Euclidean plane completed by an ideal point; completion of the affine plane by ideal points leads to the concept of a projective plane. See also Infinitely-distant elements.
Ideal point. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Ideal_point&oldid=34379