In article <406dbcda$1@news.povray.org>, "Harold" <bai### [at] 3dculturecom> 
wrote:

> Okay, I have to admit my ignorance. I don't know how modifying
> the direction vector affects the image.

It basically makes the image projection asymmetrical. A typical 
perspective camera puts the image plane centered on and perpendicular to 
the view axis. Rays come from the camera and pass through a point in 
this plane corresponding to that point in the image being rendered. 
Shearing the direction vector is like pushing the view plane to one 
side, it is the same as rendering a larger image and cropping part off 
one edge.

Hmm, while looking for a graphic to illustrate this, I found a page 
which describes this technique, calling it "off-axis projection":
http://www.cs.wpi.edu/~matt/courses/cs563/talks/stereohtml/stereo.html

And another page, comparing the pros and cons:
http://www-lsi.upc.es/~lucac/projects/stereopsis/

-- 
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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