1. A method of obtaining a three-dimensional deformation of an organ which is deformable over time and extends in a three-dimensional space from at least two sets of data representing points of said organ and corresponding to distinct times in the deformation of the organ, said method comprising the steps of: determining, in one of the sets of data, a set of points of the organ for which a correspondence with a point of another set of data is known, said set of points being termed the selection, defining at least two planes perpendicular to each other in the three-dimensional space, and explicit equations on said planes comprising unknown parameters of the deformation of the organ on said planes, calculating said unknown parameters for each of the explicit equations on each of the planes using the known correspondences for the points in the selection, extrapolating explicit equations of the known deformation on said planes to the set of points of said organ using a spatial weighting of the explicit equations on the planes perpendicular to each other.