1. A method of determining the pose of an object in a given 2D image relative to a 3D model of the object, comprising: matching points of the object in the given image with corresponding points of a base image, wherein each matched point has a corresponding 3D position in the 3D model, the 3D positions being determined by the poses of the images, wherein the pose of the base image is known; and calculating the pose of the given 2D image such that projections of 3D positions of matched points of the base image onto the given 2D image coincide approximately with the corresponding matched points of the given 2D image.