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Thread: the "ground truth" method

  1. #1
    Junior Member Newbie
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    Feb 2004
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    China P.R
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    the "ground truth" method

    Hi, can anyone please tell me how the method of "ground truth" works when generating soft shadows? Thanks.

    Amhood

  2. #2
    Advanced Member Frequent Contributor plasmonster's Avatar
    Join Date
    Mar 2004
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    739

    Re: the "ground truth" method

    I'm guessing that you mean "ground plane" shadows. This simple technique involves a projection of geometry on to a plane, presumably the ground, followed by a blending operation.

    Code :
    For a light direction L of unit length, and a 
    vertex V projected on to a plane with normal N 
    and distance D, the projected vertex V' is given 
    by
     
             D - <V|N>  
    V' = V + ---------  L
               <L|N>
     
     
    For a point light with position L, the projected
    vertex V' is given by
     
             D - <V|N>
    V' = V + --------- (L - V)
             <L - V|N>
     
     
    where <*|*> is a standard dot product.
    There are alternatives to this technique, such as stenciled shadow volumes and depth buffers, both facilitated in current hardware. The shadow volume method uses the same basic projection concept as the ground plane method above.

    There are numerous soft shadow techniques. One method involves jittering a shadow volume eminating from the light source; another solution utilizes precomputed light maps for static scenes.

    This is currently a huge research area, and there are several interesting ideas out there.

    I hope this helps.

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