Adds SV4D code

sgm/modules/diffusionmodules/sigma_sampling.py

@@ -1,5 +1,5 @@
 import torch
-
+from typing import Optional, Union
 from ...util import default, instantiate_from_config
 
 
@@ -29,3 +29,10 @@ class DiscreteSampling:
             torch.randint(0, self.num_idx, (n_samples,)),
         )
         return self.idx_to_sigma(idx)
+
+
+class ZeroSampler:
+    def __call__(
+        self, n_samples: int, rand: Optional[torch.Tensor] = None
+    ) -> torch.Tensor:
+        return torch.zeros_like(default(rand, torch.randn((n_samples,)))) + 1.0e-5