1. A computer-implemented method comprising: receiving discrete depth frames D i,j from a depth camera; calculating quadratic meshes given by X i,j =(i−i c )D i,j c d −1 , Y i,j =(j−j c )D i,j c d −1 , and Z i,j =D i,j , where i c ,j c denote coordinates of a central pixel in a depth frame, and c d is a focal length of the depth camera; detecting a presence of a particular skeletal geometry from a sequence of data frames by fitting each frame of the discrete depth frames to a skeletal model with parameters defined from 
 S={a l ∈ ,b l ∈ ,R l ∈SO (3): l∈ } where is a set of indices of line segments defined by end-points a l and b l , and its orientation in the 3D space is given by the rotation matrix R l ; segmenting the quadratic mesh into body regions by using the parameters of the skeletal model S; and fitting a positive-definite tensor spline of a spline model f d ⁡ ( x , s ) = ∑ i = 1 m ⁢ ∑ j = 0 n ⁢ w i , j ⁢ N j , k + 1 ⁡ ( s ) ⁢ f d , i * ⁡ ( x ) to a point-set P l of points that belong to a particular body region of the body regions.