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Ray tracing, regarding Turner Whitted's original paper

  1. Dec 16, 2013 #1
    As many of you may know, ray tracing was first introduced by Turner Whitted in 1979 in a paper titled "An improved illumination model for shaded display" (can be found on ACM digital library).

    On the 2nd page, in part 2 (Improved Model) there are a number of fairly simple vector calculations, unfortunately I can't understand what is vector V' (please refer to the attached screenshot), and why is it scaled by | V . N | ... I would like to ask for your thoughts on this :)

    Thanks !

    P.S.: unfortunately I can't attach the paper to my post, it is copyrighted by ACM and I think it would be illegal to do so.

    EDIT: found a link to the paper from Drexel University here

    Attached Files:

  2. jcsd
  3. Dec 16, 2013 #2


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    The diagram shows you the vector (N + V'), as the "horizontal" dotted line ending at the top of the N vector.

    So V' is the third side of the triangle with the other two sides N and (N+V'). Ini other words, V' is the V vector scaled to be the same "vertical height" as N.

    Earller N was defined as the unit vector (i.e. its length=1) normal to the surface.

    So |V.N| is the length of V, times the cosine of the angle between V and N.
  4. Dec 16, 2013 #3
    Hi AlephZero,

    Thank you so much for your reply, I appreciate it.
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