A transformation of the plane which transforms collinear points into collinear points. A projective collineation transforms every one-dimensional form projectively, and a perspective collineation is a collineation which leaves all lines through a point and points through a line invariant. In an elation, the center and axis are incident; in a geometric homology they are not. For further discussion, see Coxeter.

affine transformation | connex | correlation | elation | equiaffinity | geometric homology | perspective collineation | projective collineation