code: def forward(self, rays_d: torch.Tensor) -> torch.Tensor:
      rays_d_encoding = self.encode(rays_d)
      features = self.forward_net(rays_d_encoding)
      features = torch.sigmoid(features)
      return features
  
imports: import torch
  import torch.nn
label_desc: Use image node_id 4 for calling the NeRFBackgroundBase obj's underlying member method code with example usage: obj.forward(rays_d) and returns: features