John Skilling has used a generalization of the Hilbert curve to n-dimensions in his BayeSys software for Bayesian inference: https://www.inference.org.uk/bayesy

John Skilling has used a generalization of the Hilbert curve to n-dimensions in his BayeSys software for Bayesian inference: https://www.inference.org.uk/bayesys/ https://www.inference.org.uk/bayesys/ -- the manual describes how (pdftex will make a nice pdf), with further references, and C code is available.