Answered most your other questions below in another comment. > and what are z(t) r(t) in equation 5,6? r(t) is a position in 3D space along a camera ray of th

Answered most your other questions below in another comment. > and what are z(t) r(t) in equation 5,6? r(t) is a position in 3D space along a camera ray of the form, r(t) = origin + t * direction. z(t) is the output of our first MLP. Think of it as a 256-dimensional vector of uninterpretable numbers that represent the input position r(t) in a useful way.