POV-Ray : Newsgroups : povray.newusers : Artefact in lathe object using hollow and interior media emission : Re: Artefact in lathe object using hollow and interior media emission Server Time
25 May 2024 20:30:47 EDT (-0400)
  Re: Artefact in lathe object using hollow and interior media emission  
From: nj
Date: 21 Jan 2021 09:20:10
Message: <web.60098c7035b6182be45c73b20@news.povray.org>
William F Pokorny <ano### [at] anonymousorg> wrote:

> My current, occasionally published by tar ball, povr branch has a
> collection of solver improvements which work much more often in practice
> - especially if you turn AA on. It handles your cubic lathe scene fine,
> but yep, you have to build it yourself and povr isn't strictly backward
> compatible with POV-Ray(1).

It seems I should look into this. I hadn't planned to actually dive that deep
...... ;-)

> It would have been better to
> use a cylinder{} object. And this touches on shape trade-offs. You might
> find a better v37/v38 general solution coding your shape as an
> isosurface cylinder deformed by the cubic spline.

OK. That sounds promising. I will look into this first. Thanks for the tip!

> Aside 2: For fun, change the pigment in your just posted scene to 'rgb
> 1' and render! The povr solver changes fix those artefacts too.

Ah, nice :D
Looks like the opposite of what I had so far :\

"Bald Eagle" <cre### [at] netscapenet> wrote:

> Yeah - that's a tricky thing to ponder at first, but perhaps you can use a
> bezier_spline in your lathe, and use "degree elevation" to figure out exactly
> where your additional points need to be.

Ah, thanks! That a nice one :)

I had a look into it and wrote some python code that adds points to a bezier
spline this way (I can share the code if it helps someone else). The results are
......let's say... interesting. I have to go to over thousand points for the
artifact to vanish. Here is a gif of the results:


From plotting the curves, my degree elevation looks correct. I am, however, a
bit surprised that the thickness of the lathe is not always the same.
Specifically, it changes strongly for small numbers. I would have expected that
povray draws the exact same spline for all numbers of points.

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