"twister" <twi### [at] o2pl> wrote in message 
news:web.49a3ee97d251b6ec9ee64130@news.povray.org...
> Hi all,
>
> Maybe it is kind of silly question, but as far as I am new to PovRay I 
> can't
> deal with it. The thing is I don't understand how the list of values 
> (followed
> by points) in the spline declaration works. For linear_spline these values
> doesn't matter what is quite obvious. But for quadratic_ or natural_spline 
> they
> matters. It is written in documentation they are some parameters, but 
> nothing
> more. Where will I find some helpful informationa about spline 
> declarations?
> Because otherwise I don't know what I do. Thanks in advance.
> Best regards,
> Twister

I take it that, in the spline definition:

    spline {
      [SPLINE_IDENTIFIER] |
      [SPLINE_TYPE] |
      [Val_1, <Point_1>[,]
       Val_2, <Point_2>[,]
       ...

you're asking about Val_1, Val_2 etc.

These are fairly arbitrary values that you can think of in a number of 
different ways. It's like a 4th dimension that you can use to index how far 
through the spline you are, but you can really choose what you consider this 
index to represent.

The help suggests thinking of it as time, which is handy when you do 
animations. I usually set it so that the first physical point on the spline 
starts at 0 and the last point ends at 1. This means that in animations it's 
easy to use it with the clock variable to step along the spline in equally 
sized time slices.

When defining a curve in a scene (rather than when using it for animation) 
you can just consider it as an amount that represents how far through the 
spline definition you are. So if you still start the spline at 0 and end at 
1, then 0.5 can represent half way through the spline definition, though 
it's important to realise that this is not a distance, so it may be nowhere 
near the physical mid-point of the spline.

Any help?

Regards,
Chris B.

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