Abstract: A method of determining a transformation is provided between an image coordinate system and an object coordinate system including: providing an object coordinate system associated with the object of interest, providing a 3D model of at least part of the object of interest, wherein the 3D model comprises 3D features, providing an N-th input depth image of at least part of the object of interest, wherein an N-th image coordinate system is associated with the N-th input depth image, providing an N-th plurality of 3D features in the N-th image coordinate system according to the N-th input depth image, estimating an N-th coarse transformation between the object coordinate system and the N-th image coordinate system according to a trained pose model and the N-th input depth image, and determining an N-th accurate transformation between the N-th image coordinate system and the object coordinate system.