code: def bounding_sphere(self):
          
          from . import primitives, nsphere
          center, radius = nsphere.minimum_nsphere(self)
          minball = primitives.Sphere(center=center,
                                      radius=radius,
                                      mutable=False)
          return minball
docs: A minimum volume bounding sphere for the current mesh.
  
          Note that the Sphere primitive returned has an unpadded, exact
          sphere_radius so while the distance of every vertex of the current
          mesh from sphere_center will be less than sphere_radius, the faceted
          sphere primitive may not contain every vertex
  
          Returns
          --------
          minball: trimesh.primitives.Sphere
            Sphere primitive containing current mesh