There is a notion called the "orthogonal convex hull," or the "digital convex hull," which may be what you seek. For example, in this paper, > Karmakar, Nilanjana, and Arindam Biswas. "Construction of 3D Orthogonal Convex Hull of a Digital Object." In *International Workshop on Combinatorial Image Analysis*, pp. 125-142. Springer, Cham, 2015. [Springer link](https://link.springer.com/chapter/10.1007/978-3-319-26145-4_10). the authors define it this way: "Orthogonal convex hull of a digital object in 3D domain is defined as the minimum volume orthogonal polyhedron enclosing the object such that its intersection with an axis-parallel face plane is either empty or a collection of projection-disjoint convex polygons." <hr /> <img src="https://i.sstatic.net/wkwba.png" width="300" /> <hr /> [1]: https://i.sstatic.net/wkwba.png