Le_Forgeron <jgr### [at] freefr> wrote:
> 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))

Hi Le,

Thanks for your reply, that's very helpful.
But do you know how to smooth a 2d data set so that it is G4 continuity ?

Best,
xslittlegrass

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