Data processing method for transforming a first 3D surface (S S) which is adapted to cover a first object (O S) and is formed of a mesh of first 2D elementary surfaces into a second 3D surface (S C) which is adapted to cover a second object (O C) and is formed of a mesh of second 2D elementary surfaces, said method being characterized in that it comprises a step of iterative processing in which the transformations of the first elementary surfaces into respective second elementary surfaces are determined by carrying out in an iterative manner steps in which: a/ in a current (k+1) th iteration step, k being an integer greater than or equal to 0, for each of a plurality of couples comprising a first elementary surface and a second elementary surface derived from a transformation of the first elementary surface and having been obtained in the preceding iteration k, the projection of said second elementary surface on the plane of said first elementary surface is determined, and a current 2D transformation matrix T k + 1 t is defined for said couple, where T k + 1 t = P k t ′ P t − 1 and P t = [p n+1 - p i] i=1 to n, P k t ' = [p' n+1,k - p' i,k] i=1 to n; wherein p i, for i=1 to n, are the vertices of the first elementary surface t of the couple and p n+1 is obtained by offsetting the vertex p 1 by a normal vector of given norm to said first surface; wherein (P t) -1 is the inverse of the matrix P t when the first elementary surfaces are triangles and is a pseudo-inverse matrix of the matrix P t otherwise; wherein p' i,k, for i=1 to n, are the vertices of said projection of the second elementary surface and p' n+1,k is obtained by offsetting the vertex p' 1,k of said normal vector; b/ the second elementary surfaces obtained for the (k+1) th iteration are determined as those minimizing a function including at least the term E shape _ k + 1 = ∑ t ̃ k + 1 ∈ S ‖ P ̃ k + 1 t P t − 1 − T k + 1 t ‖ 2, wherein S is a set of second elementary surfaces t̃ k +1 determined in step k+1; T k + 1 t are the transformation matrices defined in step a/ of the (k+1) th iteration; P ̃ t k + 1 = p ̃ n + 1, k + 1 − p ̃ i, k + 1 i = 1,., n; wherein p̃ i,k +1, for i=1 to n, are the vertices of the second elementary surface t̃ k +1 as determined in the (k+1) th iteration and p̃ n +1, k +1 is obtained by offsetting the vertex p̃ 1, k +1 by a vector of said given norm normal to said second elementary surface t̃ k +1, the minimization being performed by using an iterative technique, which alternates between updating each transformation matrix T t, while keeping the matrix P̃ t fixed, and updating the matrix P̃ t while keeping the transformation matrices T t fixed. a/ in a current (k+1) th iteration step, k being an integer greater than or equal to 0, for each of a plurality of couples comprising a first elementary surface and a second elementary surface derived from a transformation of the first elementary surface and having been obtained in the preceding iteration k, the projection of said second elementary surface on the plane of said first elementary surface is determined, and a current 2D transformation matrix T k + 1 t is defined for said couple, where T k + 1 t = P k t ′ P t − 1 and P t = [p n+1 - p i] i=1 to n, P k t ' = [p' n+1,k - p' i,k] i=1 to n; wherein p i, for i=1 to n, are the vertices of the first elementary surface t of the couple and p n+1 is obtained by offsetting the vertex p 1 by a normal vector of given norm to said first surface; wherein (P t) -1 is the inverse of the matrix P t when the first elementary surfaces are triangles and is a pseudo-inverse matrix of the matrix P t otherwise; wherein p' i,k, for i=1 to n, are the vertices of said projection of the second elementary surface and p' n+1,k is obtained by offsetting the vertex p' 1,k of said normal vector; b/ the second elementary surfaces obtained for the (k+1) th iteration are determined as those minimizing a function including at least the term E shape _ k + 1 = ∑ t ̃ k + 1 ∈ S ‖ P ̃ k + 1 t P t − 1 − T k + 1 t ‖ 2, wherein S is a set of second elementary surfaces t̃ k +1 determined in step k+1; T k + 1 t are the transformation matrices defined in step a/ of the (k+1) th iteration; P ̃ t k + 1 = p ̃ n + 1, k + 1 − p ̃ i, k + 1 i = 1,., n; wherein p̃ i,k +1, for i=1 to n, are the vertices of the second elementary surface t̃ k +1 as determined in the (k+1) th iteration and p̃ n +1, k +1 is obtained by offsetting the vertex p̃ 1, k +1 by a vector of said given norm normal to said second elementary surface t̃ k +1, the minimization being performed by using an iterative technique, which alternates between updating each transformation matrix T t, while keeping the matrix P̃ t fixed, and updating the matrix P̃ t while keeping the transformation matrices T t fixed.