Question about Ray-Plane Intersection in LPG

[Vivien9324]

i noticed that the answer of the question about LPG(#35 ).
First we should set V to be (u,v,1)，i am wondering why the z-coordinate of v is 1. and if i am right, the value t is regarded as the depth of point P.

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https://www.cs.princeton.edu/courses/archive/fall00/cs426/lectures/raycast/sld017.htm
where V: (u, v, 1), N: (n1, n2, n3), d: n4 and P0: (0, 0, 0) in this work.
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