code: def bounding_primitive(self):
          
          options = [self.bounding_box_oriented,
                     self.bounding_sphere,
                     self.bounding_cylinder]
          volume_min = np.argmin([i.volume for i in options])
          bounding_primitive = options[volume_min]
          return bounding_primitive
docs: The minimum volume primitive (box, sphere, or cylinder) that
          bounds the mesh.
  
          Returns
          ---------
          bounding_primitive : trimesh.primitives.Sphere
                               trimesh.primitives.Box
                               trimesh.primitives.Cylinder
            Primitive which bounds the mesh with the smallest volume