Improving RayBundle docstrings

Summary: This changes only documentation. We want to be explicit that ray directions are not normalised (nor assumed to be normalised) but their magnitude is used.

Reviewed By: nikhilaravi

Differential Revision: D29845210

fbshipit-source-id: b81fb3da13a42ad20e8721ed5271fd4f3d8f5acb

Author: shapovalov

pytorch3d/renderer/implicit/utils.py

@@ -14,6 +14,9 @@ class RayBundle(NamedTuple):
     RayBundle parametrizes points along projection rays by storing ray `origins`,
     `directions` vectors and `lengths` at which the ray-points are sampled.
     Furthermore, the xy-locations (`xys`) of the ray pixels are stored as well.
+    Note that `directions` don't have to be normalized; they define unit vectors
+    in the respective 1D coordinate systems; see documentation for
+    :func:`ray_bundle_to_ray_points` for the conversion formula.
     """
 
     origins: torch.Tensor
@@ -36,6 +39,8 @@ def ray_bundle_to_ray_points(ray_bundle: RayBundle) -> torch.Tensor:
                 + ray_bundle.directions[i, :] * ray_bundle.lengths[i, j]
             )
         ```
+    Note that both the directions and magnitudes of the vectors in
+    `ray_bundle.directions` matter.
 
     Args:
         ray_bundle: A `RayBundle` object with fields:
@@ -70,6 +75,8 @@ def ray_bundle_variables_to_ray_points(
                 + rays_directions[i, :] * rays_lengths[i, j]
             )
         ```
+    Note that both the directions and magnitudes of the vectors in
+    `rays_directions` matter.
 
     Args:
         rays_origins: A tensor of shape `(..., 3)`