This paper describes a unified theory for autocalibration of a moving camera. The camera models can be 2D projective, 2D affine camera and 1D projective projections. The scenes can be either non-planar scenes or planar scenes and the camera may also undergoes a pure rotation. All these cases are unified into the same framework based on the direction bases. Each formulation on the direction bases is also paralleled with that on projective geometry concepts, essentially encoded by the various forms of the absolute conic. This unification provides not only a common theoretical framework, but also suggests unified parameterisation schema for estimation procedures.