BGimeno <bru### [at] gmailcom> wrote:
> Can someone think of a better way for cover the gaps left by these
> sphere_sweep (cubic_spline) curves with bicubic_patch?. I've been
> looking at before posting this message and I am stuck at the point at
> which, for the example given in the documentation I arrived to a
> self-referential loop. (in short: being a circular shape you need to
> know previously the point B to know point A and point A to calculate the
> point B).
> doc: http://www.povray.org/documentation/view/3.6.1/64/
>
> Another point is commented by clipka a 2015 post on this issue.
>
http://news.povray.org/povray.tools.general/thread/%3Cweb.54e9d43835fbd8f37a3e03fe0%40news.povray.org%3E/
>
> If it is mathematically impossible to make a perfect circle based on
> patches, I suppose that the task of adjusting them smoothly to this form
> can not be carried out either.
>
> Any help or idea to the respective one is welcome, thank you very much
> in advance.
>
> Bruno Gimeno

Hi Bruno - IIRC, you can't use a bezier spline to make a circle.
https://stackoverflow.com/questions/1734745/how-to-create-circle-with-b%C3%A9zier-curves
 But you may be able to sufficiently approximate it with several end-to-end.

When it comes to the patch, if you want to specify the points that the patch
will intersect, you need a matrix of 3x3 patches.  Otherwise, with only one
patch, you're left specifying the control points of the bezier splines, which
aren't on the surface of the patch.

I started working to address exactly this  a while back, and got to the point
where I was just ripping my hair out.

http://news.povray.org/povray.binaries.animations/thread/%3Cweb.56d9fbdd155fef445e7df57c0%40news.povray.org%3E/?mtop=40
6768&moff=22

http://news.povray.org/povray.binaries.animations/thread/%3Cweb.56ded7545a67670a5e7df57c0%40news.povray.org%3E/

http://news.povray.org/povray.binaries.images/thread/%3Cweb.56d9fcdc4ecdf5285e7df57c0%40news.povray.org%3E/





Maybe we look at it with fresh eyes and get a good 3x3 patch that works.

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