code: def sample_alpha(self, xyz_sampled):
      xyz_sampled = self.normalize_coord(xyz_sampled)
      alpha_vals = F.grid_sample(
          self.alpha_volume,
          xyz_sampled.view(1, -1, 1, 1, 3),
          align_corners=True,
      ).view(-1)
  
      return alpha_vals
  
imports: import torch
  import torch.nn
  import torch.nn.functional
  from .sh import eval_sh_bases
  import numpy
  import time
label_desc: Use image node_id 2 for calling the AlphaGridMask obj's underlying member method code with example usage: obj.sample_alpha(xyz_sampled) and returns: alpha_vals