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


Thank you for taking the time to go through the problem.
So basically the < x, y, z > coordinates are coming from a numerically simulated
soft robot and the entire shape of the robot changes over time. So I was trying
to create a spline through these points that move in the 3d space. I agree that
the splines will be of different lengths depending on the location of control
points but this is what I am trying to fix. As the spline represents a soft
robot that is capable of only changing its shape keeping the length constant.
I hope this clears some of your doubts.

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