Preserving convexity using piecewise cubic interpolation. - Ken Brodlie; Sohail Butt (Comput. Graph., 1991)

Preserving positivity using piecewise cubic interpolation. - Sohail Butt; Ken Brodlie (Comput. Graph., 1993)

Visualization of surface data to preserve positivity and other simple constraints. - Ken Brodlie; Petros M. Mashwama; Sohail Butt (Comput. Graph., 1995)

Non-negative rational spline interpolation. - Malik Zawwar Hussain; Muhammad Sarfraz 001; Sohail Butt (IV, 1997)

A Rational Spline for Visualizing Positive Data. - Muhammad Sarfraz 001; Malik Zawwar Hussain; Sohail Butt (IV, 2000)

Visualization of shaped data by a rational cubic spline interpolation. - Muhammad Sarfraz 001; Sohail Butt; Malik Zawwar Hussain (Comput. Graph., 2001)