In article <3c741fab@news.povray.org> , "Rune" <run### [at] mobilixnetdk>
wrote:

>> Is the following what you are suggesting:
>>
>> prism
>>  cubic_spline -> catmull_rom_spline
>
> Yes.
>
>> lathe
>>  cubic_spline -> catmull_rom_spline
>
> Yes.
>
>> spline
>>  cubic_spline -> natural_cubic_spline
>
> Yes.
>
> And if we're lucky Mark Wagner will also add the catmull_rom_spline type, so
> that spline will have both natural_cubic_spline and catmull_rom_spline.

In fact, I think the current implementation is flawed as it ignores everything
else in POV-Ray.  If catmull-rom splines cannot be added to 3.5 in time the
whole spline thingy should be dropped as the current implementation would only
cause needless confusion and conflict with everything else in POV-Ray.

>> sphere_sweep
>>  cubic_spline -> natural_cubic_spline
>
> No, sphere_sweep don't use the keyword cubic_spline. It use the keyword
> catmull_rom_spline, and this shouldn't be changed IMO. So no changes in
> sphere_sweep.

In this case, I think leaving "cubic_spline" as is and just changing the
keyword for the spline object to "natural_cubic_spline" or better
"natural_spline" is more appropriate.  In particular because natural cubic
splines seem to be less useful for modeling than Catmull-Rom splines.  This is
the obvious conclusion to draw from their use (or better lack of it) in
POV-Ray and elsewhere.

I also checked on the web and a few computer graphics books, and the use of
the term "cubic spline" as a name for a class of spline is not as frequently
used.  It might be mathematically correct, but if the widespread use is more
simplified in the field of computer graphics, my vote is for going with what
everybody else uses rather than the mathematically correct term.


    Thorsten

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

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