The invention notably relates to a computer-implemented method for designing a three-dimensional modeled object that represents a physical entity. The method comprises providing sample points; determining a volumetric function, within a predetermined class of volumetric functions, as the optimum of an optimization program that explores orientation vectors defined at the sample points, wherein the optimization program penalizes a distance from the explored orientation vectors; and fitting the sample points with an isovalue surface of the volumetric function, wherein the program further penalizes oscillations of the fitted isovalue surface.