1. A system, comprising: a memory; and one or more processing devices configured to: determine intersection points of a representation of a surface in an image space with cubes defining the image space, the surface defining a surface of an object; and determine an estimated mass of at least a portion of the object by: determining an estimated mass contribution of a first set of cubes contained entirely within the representation of the surface; determining an estimated mass contribution of a second set of cubes having intersection points with the representation of the surface; and estimating a mass of the at least a portion of the object based on the estimated mass contribution of the first set of cubes and the estimated mass contribution of the second set of cubes.