code: def test_ball_example(self):
      N = 30
      axis_tensor = torch.arange(0, N)
      X, Y, Z = torch.meshgrid(
          axis_tensor, axis_tensor, axis_tensor, indexing="ij"
      )
      u = (X - 15) ** 2 + (Y - 15) ** 2 + (Z - 15) ** 2 - 8**2
      u = u[None].float()
      verts, faces = marching_cubes_naive(
          u, 0, return_local_coords=False
      )
      verts2, faces2 = marching_cubes(u, 0, return_local_coords=False)
      self.assertClose(verts2[0], verts[0])
      self.assertClose(faces2[0], faces[0])
      verts3, faces3 = marching_cubes(
          u.cuda(), 0, return_local_coords=False
      )
      self.assertEqual(len(verts3), len(verts))
      self.assertEqual(len(faces3), len(faces))
  
imports: import os
  import pickle
  import unittest
  import torch
  from pytorch3d.ops.marching_cubes import marching_cubes, marching_cubes_naive
  from .common_testing import get_tests_dir, TestCaseMixin
label_desc: Use image node_id 9 for calling the TestMarchingCubes obj's underlying member method code with example usage: obj.test_ball_example() without return types