KFCurve Velocity, How is it Used?

[Anonymous]

Hi All,

Long time lurker, first time poster here.

I'm curious as to the actual math behind a bunch of the KFCurve cubic interpolation. As I saw here http://forums.autodesk.com/t5/FBX-SDK/Exact-kind-of-curves-and-their-matrices/td-p/4103962 it seems that, for cubic interpolation, that the KFCurve evalutation is using DeCasteljau's Algorithm between two points. It is using the left/right derviatives for particular key frames to produce the "P1" and "P2" in the algorithm.

So far, so good. I can guess as to how the left/right derviates for a key frame are computes based on the TagentMode of the key frames (TCB, user specified, auto/catmull rom, etc.). What I don't see anywhere is how the left/right velocity is used in the interpolation calculation. I don't see much about velocity as a whole in general honestly. I see some mentioning of

"Velocity settings speed up or slow down animation on either side of a key without changing the trajectory of the animation. Unlike Auto and Weight settings, Velocity changes the animation in time, but not in space."

So how, mathematically, is the velocity used? Thanks!

[Anonymous]

Hi All,

Long time lurker, first time poster here.

I'm curious as to the actual math behind a bunch of the KFCurve cubic interpolation. As I saw here http://forums.autodesk.com/t5/FBX-SDK/Exact-kind-of-curves-and-their-matrices/td-p/4103962 it seems that, for cubic interpolation, that the KFCurve evalutation is using DeCasteljau's Algorithm between two points. It is using the left/right derviatives for particular key frames to produce the "P1" and "P2" in the algorithm.

So far, so good. I can guess as to how the left/right derviates for a key frame are computes based on the TagentMode of the key frames (TCB, user specified, auto/catmull rom, etc.). What I don't see anywhere is how the left/right velocity is used in the interpolation calculation. I don't see much about velocity as a whole in general honestly. I see some mentioning of

"Velocity settings speed up or slow down animation on either side of a key without changing the trajectory of the animation. Unlike Auto and Weight settings, Velocity changes the animation in time, but not in space."

So how, mathematically, is the velocity used? Thanks!

[Anonymous]

Any help would be greatly appreciated. I'm not asking for any code (though some example code would be useful), but more of a mathematical explanation of what the velocity does. I'm unclear on what it does.

Thanks!

[Anonymous]

Any help would be greatly appreciated. I'm not asking for any code (though some example code would be useful), but more of a mathematical explanation of what the velocity does. I'm unclear on what it does.

Thanks!

[Anonymous]

It seems no one knows how these are used. Bummer 

Docs say

"Velocity settings speed up or slow down animation on either side of a key without changing the trajectory of the animation. Unlike Auto and Weight settings, Velocity changes the animation in time, but not in space."

Which is fine as a concept, but does anyone know the math (or an example)?

Also, anyone know what the "Time Independent" attribute means conceptually? I know what it means in English.

[Anonymous]

It seems no one knows how these are used. Bummer 

Docs say

"Velocity settings speed up or slow down animation on either side of a key without changing the trajectory of the animation. Unlike Auto and Weight settings, Velocity changes the animation in time, but not in space."

Which is fine as a concept, but does anyone know the math (or an example)?

Also, anyone know what the "Time Independent" attribute means conceptually? I know what it means in English.