as implemented in adobe photoshop / illustrator vector gradient, smooth, scalable
parametric surfaces - surface represented by parametric equations coons patch - simplest parametric surface ferguson patch
Image Vectorization using Optimized Gradient Meshes - microspft general discussion about gradient meshes https://sci-hub.se/https://doi.org/10.1145/1276377.1276391 monotonic 1D cubic spline interpolation
diffusion curves general diffusion curves https://sci-hub.se/https://doi.org/10.1111/cgf.12812
ply - standford triangle format file format for storing objects described as polygons. does not include parametric patches, CSD operations, triangle strips
obj file format - wavefront supports free form geometry