1. A system comprising: an aligner to align an initial position of a hierarchically rigid model with an object in an image, said hierarchically rigid model represented by a plurality of dots associated with alignment points, initial and secondary anatomic points, and by contour points; and wherein contour points define contour lines; a modelizer to adjust parameters of said model to match said model to contours of said object, given said initial alignment; and means to enable a user to operate at least one of said aligner and said modelizer interactively; wherein said initial position alignment comprises said aligner positioning said alignment points at locations associated with extremities of said object, and wherein said parameters adjustment comprises said modelizer matching said rigid model in stages to correct for noise in each stage, said stages comprising: determining a position of said model by positioning said initial anatomic points relative to said alignment points; correcting anatomic positioning of said model by positioning said secondary anatomic points relative to said initial anatomic points; defining geometrically shaped active regions in said model associated with segments of said contour lines; matching said contour lines to contour edges in said object.