"Kenneth" <kdw### [at] earthlinknet> wrote in message 
news:web.484b4a43784caf0d78dcad930@news.povray.org...
> "Chris B" <nom### [at] nomailcom> wrote:
>
> I do feel sorry for new users trying to make sense of the trace operation, 
> given
> the short and somewhat perfunctory explanation of it. It's such a powerful
> feature of POV-Ray! But some of the documentation just isn't as clear as 
> it
> should be.

I do remember the trace function being quite difficult to get my head around 
when I first used it, but now, when I look at the help entry it seems fairly 
straight forward. I don't know whether the help entry has been updated over 
the years or whether it's just that the answer makes sense when you already 
know it.

Maybe this is a prime example of where the wiki at http://wiki.povray.org/ 
could be used to collaboratively develop a clear and succinct 'how-to' 
explanation suitable for newer users.

> ... Another item of
> confusion: Somewhere above the trace explanation, it says, "The following 
> are
> the functions which return vector values."  The important word being 
> RETURN.
> But there are other functions following trace that actually DON'T return 
> any
> value (vnormalize being one.) Pity the poor new user trying to understand 
> all
> of this!

The vnormalize function does return a value, which is a unit length vector 
of the vector you pass it as a parameter. The returned value can be assigned 
to a variable using the #declare or #local statement or can be used inline 
in your SDL. The trace function is one of a small number of functions that 
requires a vector identifier as a parameter so that the function can update 
it, thereby effectively returning two values.

Regards,
Chris B.

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