1. A method of tracking movement of an object portion in three-dimensional (3D) space, the method including: selecting five observation points on a curved volumetric model fitted to a portion of a real world object, wherein one of the observation points is at a center of the curved volumetric model and the other four observation points are along a perimeter of the curved volumetric model; capturing at times t0 and t1 projections of at least the four perimeter observation points in at least a first image plane of at least one camera, wherein the object moved between t0 and t1; calculating a retraction of the four perimeter observation points at time t1 to their positions at t0, including using the four perimeter observation points to: map the captured projections of the perimeter observation points at t0 to a first image plane; and calculate orientation of a second image plane such that the captured projections of the perimeter observation points at t1 to the second image plane are collinear with respective projections in the first image plane with respect to the retracted center observation point; and determining at least translation of the curved volumetric model between the times t0 and t1 using the calculated orientation of the second image plane.