Jellby <jel### [at] m-yahoocom> wrote:
> - In section 6.10.1 it says phonton mapping uses "backwards ray-tracing"... 
> is this right? I thought it used foreward raytracing.

  It's "photon" and "forward" ;)

  But anyways, there's a problem with this. The problem is that some people
use one term while other people use the other, for the same thing.

  AFAIK _technically_ the correct term for photon mapping is "forward
raytracing".
  Since raytracing simulates how light moves from light sources to the
camera, reflecting from surfaces. If this is done by shooting rays from
light sources, then it's "forward raytracing", as it does exactly what
it simulates.
  However, due to efficiency reasons it's more efficient to do it the
other way around: To shoot rays from the camera and see how it bounces
from the surfaces to the light sources. Because this is done in the reverse
direction, it's called "backward raytracing".

  However, some authors have mixed up these concepts, AFAIK erroneusly.
They consider "regular raytracing" to be "forward" and the other one
"backward", as it's reversed compared to the "regular way". As far as
I know, this is a mistake and misunderstanding. However, due to how
popular this has been, it's now very difficult to force anyone to use
these terms in one way or another.

  Personally I prefer using the techincally correct terms, as I'm a
perfectionist, but I can't force anyone to do it as well.

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