Smooth surface interpolation using patches with rational offsets
  We present a new method for the interpolation of given data points and associated normals with surface parametric patches with rational normal fields. We give some arguments why a dual approach is the most convenient for these surfaces, which are traditionally called Pythagorean normal vector (PN) surfaces. Our construction is based on the isotropic model of the dual space to which the original data are pushed. Then the bicubic Coons patches are constructed in the isotropic space and then pulled back to the standard three dimensional space. As a result we obtain the patch construction which is completely local and produces surfaces with the global G1~continuity. 
Miroslav L\'avi\v{c}ka, Zbyn\v{e}k \v{S}\'ir, and Jan Vr\v{s}ek
cs.GR