Mike wrote:
> Hermann_Vosseler wrote:
> ...
> 
> So for the perspective camera, specifying angle after direction will
> override the value give in diection? I presume it works both ways, i.e.
> angle before direction means angle is overridden? I'll have to experiment
> with this on various camera types.
> 


(I can't look it up in the source to make it 100% shure at the moment.)

The perspective camera has only the "baseic parameters" location, 
direction, up and right. I.e. they need to be defined when the
rendering starts.

angle, sky and look_at are resolved in the parser.
When the parser e.g. finds a "angle" keyword, it takes the
right vector defined *at that moment* and modifies the direction
vector so the image will show the given angle.

To say it the other way round: perspective camera has no
parameter "angle". When "angle" is encountered, the parameter
"direction" ist modified, but the float value given behind the
"angle" keyword is not saved outside the parser. If you specify
"direction" again later in the camera definition, the
previous direction value (and thus the effect of the your
angle keyword) ist owerwritten.
The same holds true for look_at
If you specify direction again after the look_at or if you
rotate your camera, the effect of the look_at-statement is lost.


But -- on the contrary -- the panoramic-type cameras *do have*
a "angle" property, i.e. for this cameras "angle" is needed by
the raytracer itself (it needs to know how much of the image
cylinder has to be scanned)
On the other hand some cameras don't use direction. Bottom line:
rather confusing, can't find a simple rule.



Hermann

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