[x3d-public] cubic spline, step interpolation

[Don Brutzman]

Andreas, this sounds like an excellent rationale to modify the X3D spline interpolators in X3D v4 for better alignment with glTF.

When ready, if you might state the precise gap issue and suggest an improvement, that would be great.  We'll enter it in Mantis Issue Tracker for continued consideration.

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On 7/31/2018 4:06 AM, Andreas Plesch wrote:
> As I am looking to add glTF animation support for x3dom, I am considering convenient ways to do cubic spline and step wise interpolation with x3d interpolators.
> glTF has three modes of interpolation: linear, cubic spline, step.
> 
> Linear corresponds to the linear interpolation of the regular x3d interpolators.
> 
> Step produces jumps at key times, and can be represented with x3d interpolators also, by repeating keys. However, implementation could be optimized for a special step mode.
> 
> Cubic spline almost corresponds to the x3d spline interpolators but not exactly. With glTF, the velocity derived tangent can be different towards and away from a key frame, while in x3d there is only a single velocity. Also, in glTF, the tangents are requied and part of a 3 tuple for each frame. This makes computing the cubic spline interpolation straightforward and performant.
> 
> So it turns out to be most convenient and efficient to forgo the x3d spline interpolators and instead add a mode SFString init only field to the regular interpolators with a 'linear' default. I currently have it not exposed declaratively and for use with glTF only but why not expose it.
> 
> Such a mode field allows for optimization of step and cubic spline interpolation over regular, and NURBS interpolators, and allows for full glTF animation support.
> 
> Other browsers may have similar goals but likely differing strategies which would be great to hear about.
> 
> Any feedback or comment much welcome,
thank you

all the best, Don
-- 
Don Brutzman  Naval Postgraduate School, Code USW/Br       brutzman at nps.edu
Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA   +1.831.656.2149
X3D graphics, virtual worlds, navy robotics http://faculty.nps.edu/brutzman