Question about the relative viewing direction.

[Fanqyu]

Hi, thanks for your great work!
There is a question that, in your implementation, the relative viewing direction is $\mathbf{v}_{tar} - \mathbf{v}_{proj}$, where $\mathbf{v}_{tar}$ means $\mathbf{v}_{query \ camera} - \mathbf{v}_{sample \ points}$ and $\mathbf{v}_{proj}$ is also like this.
But in the paper, it says that $\Delta \mathbf{d} = \mathbf{d} - \mathbf{d}_{i}$.
As is known, the direction used in NeRF is from camera pointing to sample points. So why do you design it in the opposite direction here?
And, I tried to understand it, but I'm not sure if it's correct. In my understanding, the radiance (RGB) emitting from sample points to target camera, which is like the ray emitts into the eye, so the relative direction is designed in this way. Am I right?
Looking forward to your reply.