POV-Ray : Newsgroups : povray.newusers : Length of spline object changes during animation : Re: Length of spline object changes during animation Server Time
2 Oct 2022 18:47:18 EDT (-0400)
  Re: Length of spline object changes during animation  
From: Bald Eagle
Date: 17 Aug 2022 15:20:00
Message: <web.62fd3f2970f1e1be1f9dae3025979125@news.povray.org>
"Aj" <nomail@nomail> wrote:
> Hello everyone,
>
> I am pretty new to povray and I have the following code, where I get the x,y,
> and z coordinates of 6 different points from a simulation and then create a
> sphere sweep through these points. But the problem is the length of this object
> changes with time i.e. as the points move, the sphere sweep object appears to
> change size. If you look at the picture attached then the white and green
> objects appear to be of different lengths.
>
> Any suggestion will be really helpful.


> I have been trying to do something like shown in this video:
>
> https://www.cosseratrods.org/videos/RALvideos/Case2-front_view_web.mp4

So, without any real idea what's going on, an in the absence of any detailed
explanation, I'll speculate that you're trying to model some kind of
semi-flexible/stretchable filament that's supposed to move around based on some
kind of movement of the endpoint, or a physical particle system (your
"simulation").

So,

Either all of your <x, y, z> data is coming straight from the simulation, or

You need to calculate the (approximate) length of your spline, and then after
moving the control points, find some way to jimmy them so that you're preserving
the overall length within some constraints as defined by the elasticity of the
filament, etc. before rendering the next frame of the animation.   And that sure
doesn't sound trivial.


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