Shape preserving splines

[andrewwinters5000]

It would be a nice feature to add an additional spline type that is shape preserving for geometric data. This would help create more realistic representations of real world bottom data without the need for excessive smoothing. This type of cubic spline sacrifices continuity of the second derivative in order to constrain shape and/or prevent overshoots in the result.

Some references:

• J. E. Lavery, Shape-preserving, multiscale interpolation by bi- and multivariate cubic splines, Computer Aided Geometric Design. doi:10.1016/S0167-8396(01)00034-6.
• Davydov, O., Zeilfelder, F. Scattered Data Fitting by Direct Extension of Local Polynomials to Bivariate Splines. Advances in Computational Mathematics. https://doi.org/10.1023/B:ACOM.0000032041.68678.fa