In article <3eaa9156@news.povray.org> , Philippe Debar <phd### [at] wanadoobe>
wrote:

> Yes, but why ? To my non-programmer's ears, it does not sound more
> complicated to rotate the vectors instead of defining new ones.

It is rather complicated, but without it there would be cases for which
there is more than one solution which way the camera could be pointing.
Further, the look_at vector is of no use when actually creating camera rays
because it does not contain enough information on its own together with the
location.  That is why up, right and sky have defaults.

The key about understanding, or even trying to understand how the various
camera parameters interact (and have to interact to work together at all in
certain cases), is to understand that many are redundant ways to specify the
same information:

All you need is the up, right and direction vectors to create every possible
perspective camera specification that uses a combination of up, right,
direction, look_at, angle, sky and location.  To make it even more
complicated, other camera types need to make use only of certain aspects of
these parameters (i.e. the vector length), or they need additional
parameters (like the spherical camera).

So don't worry - without seeing the source code in action step by step, I
would never have understood what exactly is happening and why.

    Thorsten

____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

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