Why adding a negative sign to the ray direction in NeuRay?

[thucz]

Hi! I do not understand why here you add a negative sign.

NeuRay/network/render_ops.py

Line 37 in 939af16

que_dir = -directions / torch.norm(directions, dim=2, keepdim=True) # qn,rn,3

[liuyuan-pal]

Hi, I use the direction from the scene to the camera here. You may also use the direction from the camera to the scene.

[thucz]

Thanks!
But I still have another question. The code considers that |depth|<1e-4 is invalid. But in OpenCV camera coordinate system, when the depth of a 3D sample point is negative, the value should be invalid as its position is behind the camera. So I think depth < 1e-4 should be invalid.

NeuRay/network/render_ops.py

Line 101 in 939af16

invalid_mask = torch.abs(depth)<1e-4