1. A method of real-time camera tracking comprising: receiving a sequence of depth map frames from a moving mobile depth camera, each of a plurality of the depth map frames comprising a plurality of depth values at a plurality of image elements, the plurality of depth values being related to a distance from the mobile depth camera to a surface in the scene captured by the mobile depth camera; tracking the position and orientation of the mobile depth camera by computing registration parameters for the plurality of the depth map frames, the registration parameters being parameters of a transformation for aligning a first depth map frame and a preceding depth map frame; wherein computing the registration parameters comprises using an iterative process to: identify corresponding points in pairs of depth map frames without computing shapes depicted within the pairs of depth map frames and by using a parallel computing unit to optimize an error metric applied to the identified corresponding points such that the error metric is applied a plurality of the identified corresponding points in parallel.