"Trevor Quayle" <Tin### [at] hotmailcom> wrote in message
news:3bcddffa$1@news.povray.org...
> In 3.5, you would define a spline as follows:
>
> #declare MySpline =
> spline {cubic_spline
>     -.25, <0,0,-1>
>     0.00, <1,0,0>
>     0.25, <0,0,1>
>     0.50, <-1,0,0>
>     0.75, <0,0,-1>
>     1.00, <1,0,0>
>     1.25, <0,0,1>
>   }
>
> And implement it using MySpline(val)
>
> Does val not indicate the position along the spline, i.e, 0.1 would be 10%
> along the length of the spline etc.?
>

No. MySpline(0.1) calculates the value of the spline where the spline
parameter=0.1
In your example the distances between each 'control point' is the same, but
consider the following

#declare MySpline=
 spline {
  cubic_spline
  -0.25, <0,0,0>
   0.00,<1,0,0>
   0.25,<2,0,0>
   0.50,<4,0,0>
   0.75,<8,0,0>
   1.00,<16,0,0>
   1.25,<32,0,0>
  }

In the above case MySpline(0.1) will give me a value of <1.249,0.000,0.000>
which
is definatly not 10% of the way along the spline

Gail
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* gsh### [at] monotixcoza                *   Step into the abyss,           *
* http://www.rucus.ru.ac.za/~gail/   *   and let go.          Babylon 5 *
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