 Spherical coordinates take this a step further by converting the pair of cylindrical coordinates ("r", "z") to polar coordinates ("ρ", "φ") giving a triple ("ρ", "θ", "φ").A point in the plane may be represented in "homogeneous coordinates" by a triple ("x", "y", "z") where "x"/"z" and "y"/"z" are the Cartesian coordinates of the point.This introduces an "extra" coordinate since only two are needed to specify a point on the plane, but this system is useful in that it represents any point on the projective plane without the use of infinity.