Christian Perwass Rida T. Farouki Lyle Noakes A geometric product formulation for spatial Pythagorean hodograph curves with applications to Hermite interpolation. 220-237 2007 24 Computer Aided Geometric Design 4 http://dx.doi.org/10.1016/j.cagd.2007.01.002 db/journals/cagd/cagd24.html#PerwassFN07