1. A method of processing data defining at least three polyhedra, each respective polyhedron comprising a plurality of planar faces in a three-dimensional space defining a volume within which at least part of a subject object lies, to generate a 3D computer model of the subject object comprising points in the three-dimensional space representing points on the surface of the subject object connected to form a polygon mesh, the method comprising: calculating points in the three-dimensional space representing points on the surface of the subject object by calculating the respective points at which a predetermined number of planar faces from the polyhedra intersect; assigning an identification to each calculated point representing a point on the subject object in dependence upon the planar faces which meet at the point; and after calculating the points representing points on the subject object and assigning identifications thereto, connecting the points in dependence upon the assigned identifications to generate a 3D computer model comprising a polygon mesh representing the surface of the subject object.