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).(adsbygoogle = window.adsbygoogle || []).push({});

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 Universityhere

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# Ray tracing, regarding Turner Whitted's original paper

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