AABB normalized_positions to [-1, 1]

Previously, SceneBox.get_normalized_positions() returned a value in 0,1.
This was fine for InstantNGP and Nerfacto, which use these values directly in an MLP.
For TensoRF though, this was an error because grid sample expects values in the range [-1,1].
Thus, I think only 1/4th of the encoding planes were actually being used, and half of the
encoding lines were.

nerfstudio/field_components/encodings.py

@@ -423,6 +423,13 @@ def get_out_dim(self) -> int:
         return self.num_components * 3
 
     def forward(self, in_tensor: TensorType["bs":..., "input_dim"]) -> TensorType["bs":..., "output_dim"]:
+        """Compute encoding for each position in in_positions
+
+        Args:
+            in_tensor: position inside bounds in range [-1,1],
+
+        Returns: Encoded position
+        """
         plane_coord = torch.stack([in_tensor[..., [0, 1]], in_tensor[..., [0, 2]], in_tensor[..., [1, 2]]])  # [3,...,2]
         line_coord = torch.stack([in_tensor[..., 2], in_tensor[..., 1], in_tensor[..., 0]])  # [3, ...]
         line_coord = torch.stack([torch.zeros_like(line_coord), line_coord], dim=-1)  # [3, ...., 2]

nerfstudio/fields/tensorf_field.py

@@ -85,6 +85,7 @@ def __init__(
 
     def get_density(self, ray_samples: RaySamples):
         positions = SceneBox.get_normalized_positions(ray_samples.frustums.get_positions(), self.aabb)
+        positions = positions * 2 - 1
         density = self.density_encoding(positions)
         density_enc = torch.sum(density, dim=-1)[:, :, None]
         relu = torch.nn.ReLU()
@@ -94,6 +95,7 @@ def get_density(self, ray_samples: RaySamples):
     def get_outputs(self, ray_samples: RaySamples, density_embedding: Optional[TensorType] = None) -> TensorType:
         d = ray_samples.frustums.directions
         positions = SceneBox.get_normalized_positions(ray_samples.frustums.get_positions(), self.aabb)
+        positions = positions * 2 - 1
         rgb_features = self.color_encoding(positions)
         rgb_features = self.B(rgb_features)