1. A method of real-time camera tracking comprising: receiving a sequence of depth map frames from a moving mobile depth camera each depth map frame comprising a depth value at each image element that depth value 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 each depth map frame, those registration parameters being parameters of a transformation for aligning each 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 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 to each of the identified corresponding points in parallel.