Le 29/05/2014 04:01, xslittlegrass nous fit lire :
> I'm trying to make a lathe object from some data points. My data points look
> quite smooth, but the generated lathe object looks not smooth, it looks kind of
> like be constructed from flat rings. Do you know why the lathe object is not
> smooth and how to solve this problem? I tried different kind of spline but that
> doesn't help.
> Any suggestions and comments are appreciated.
> 
> This is how the data points look like
> 
> http://imgur.com/Vkkk5Rq
> 
> and this is how the lathe object looks like
> 
> http://imgur.com/2UxKgwD
> 

Greetings,

The surface is smooth... but we have to talk a bit about smoothness.

In math, it's called continuity, and there is 5 degrees of it, from G0
to G4.

cubic spline provides G2.

Control of highlights need more than just G2. Your points, from spline,
are G2, but not globally G4 and bad luck strikes: you have multiple
jumps at G3 & G4, which you see.

Attached are the same scene with a reduction to half and quarter the
number of points. you will see there is less change of highlights. Yet,
the problem is not the number of points, but their jumps in third and
fourth derivatives.

You will need to generate them for G4 by hand (or outside povray), if
you want no highlight, as spline of lathe can only warrant G2.


-- 
IQ of crossposters with FU: 100 / (number of groups)
IQ of crossposters without FU: 100 / (1 + number of groups)
IQ of multiposters: 100 / ( (number of groups) * (number of groups))

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