On 30 Mar 2004 14:56:43 -0500, Eamon Caddigan <eca### [at] uiucedu> wrote:
> One scene has the following camera definition:
> camera {
>   location <0.0000, 0.0000, -2.0000>
>   look_at <0.0000, 0.0000, -0.0000>
>   up <0.0000, 6.0000, 0.0000>
>   right <8.0000, 0.0000, 0.0000>
>   direction <-0.0000, -0.0000, -4.0000>
> }
>
> If the direction vector begins at the location point, it's pointing
> "away" from the look_at point. Maybe the problem is my comprehension of
> POV-Ray's camera model.

With POV-Ray's camera model, there is no way to look "away" from the 
look_at point.
'look_at' (if specified) is always applied after 'direction'. That makes 
your camera statement equivalent to:

camera {
   location <0, 0, -2>
   up <0, 6, 0>
   right <8, 0, 0>
   direction <0, 0, -4>
   look_at <0, 0, 0>
}

...which, in turn, is equivalent to:

camera {
   location <0, 0, -2>
   up <0, 6, 0>
   right <8, 0, 0>
   direction vnormalize(<0,0,0> - <0,0,-2>)*4
}

or

camera {
   location <0, 0, -2>
   up <0, 6, 0>
   right <8, 0, 0>
   direction <2, 3, sqrt(2)>	// Arbitrary vector with length 4
   look_at <0, 0, 0>
}


When you specify all three of 'up', 'right' & 'look_at', the actual 
direction of 'direction' no longer matters. Only its length matters, since 
that determines the field of view (unless you also specify 'angle').

You might want to take a closer look at section 6.4.1 of the docs, 
especially 6.4.1.4.


---
FE (on topic this time)

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