In article <4148cd20@news.povray.org>, Warp <war### [at] tagpovrayorg> 
wrote:

>   The disadvantage is that since the ray must keep straight even after
> transforming it, only linear transformations are possible. (This is
> the reason why there are no non-linear transformations in POV-Ray.)

A tiny correction: only affine transformations are possible. Scaling, 
rotation, and shearing (and combinations of these) are linear 
transforms, translation and combinations of translation with the others 
are affine transforms. What you can't do are things like transforming a 
cylinder into a cone, or adding ripples to a plane. The transformation 
must preserve collinearity, points on a straight line must remain on a 
straight line after transformation, and it must be invertible (or 
reversible).

Basically, if you have a torus at < 1, 2, 3>, the camera rays being 
tested against that torus are translated by <-1,-2,-3>, so they hit the 
torus at the origin. The points are then transformed back to their 
"global" positions.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: <chr### [at] tagpovrayorg>
http://tag.povray.org/

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