John E. Lavery Shape-preserving, first-derivative-based parametric and nonparametric cubic <i>L</i><sub>1</sub> spline curves. 276-296 2006 23 Computer Aided Geometric Design 3 http://dx.doi.org/10.1016/j.cagd.2005.11.002 db/journals/cagd/cagd23.html#Lavery06