"twister" <twi### [at] o2pl> wrote in message 
news:web.49a40439cf14bf60c9ee64130@news.povray.org...
> "Chris B" <nom### [at] nomailcom> wrote:
>> 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.
>
> To be honest I cannot say these values are arbitrary ones because they 
> have
> strong impact on the spline shape. Besides, following spline is wrong and
> povray returns an error: "Parse Error: Degenerate cylinder, base point = 
> apex
> point." It means I cannot define these values in whatever manner I like.
>
> #declare mySpline = spline {
> quadratic_spline
> 1, <0,0,0>,
> 2, <1,1,0>,
> 3, <2,1,0>,
>
>
> }

By 'arbitrary' I meant they don't represent anything specific and can have 
more or less any values that you like.
The above spline didn't return an error when I just pasted it into a scene 
file and ran it through the parser and the error you mention relates to a 
cylinder rather than a spline, so I suspect it was generated by another part 
of your scene file.


>
>> 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.
>
> I can think of these values as a "timestamps", but they shouldn't change 
> the
> spline shape!

I don't think they do change the shape of the spline.

>> Any help?
>
> Still confused...

Well it may be one of those things that just suddenly clicks when someone 
describes it in a certain way, so I'll leave it to others to have a go.

Regards,
Chris B.

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