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Pencil of lines

A set of concurrent lines in \ensuremath{{\cal P}^2}, that is, a set of lines passing through the same point, is a one-dimensional projective space called a pencil of lines. That the space is one-dimensional is the obvious result of applying the principle of duality: a set of concurrent lines is the same as a set of collinear points. We will say no more about a pencil of lines other than to mention that it exists and that it has several applications in computer vision.

Stanley Birchfield