Importing Mfnanimcurve Keys

[jeffm3]

I'm trying to import some animation keys into Maya, and I've run into a small problem with importing
rotation keys. Apparently, to use addKey(), I must convert my quaternions to Euler angles. I use Maya's
math functions to do it, which seems easy enough:

MQuaternion q( myquat.x, myquat.y, myquat.z, myquat.w );
MEulerRotation euler = q.asEulerRotation();

animCurve.addKey( MTime(t, MTime::kSeconds), euler.x );
(etc... for each x,y,z component)

This works OK for the most part. However, when I play back my animation in Maya, I can see some bad
rotations happening. Joints seem to be rotating in the wrong direction.

Assuming the data is good and the calculations are correct, what can I do to fix this?

[rob-bateman]

consider each new key value with respect to it's last. It shouldn't ever be more than 180 degrees away from the last key (big assumption, but it works for the most part). basically if you look in the anim curve editor, you'll probably see say, an x rotation value increasing until 180 degrees then it wraps around to -180 degrees. You basically need to check that this is happening, and add 360 to the value (probably in a while loop so you can carry on rotation past 720 degrees and onwards). It annoys me too

[jeffm3]

Thanks for the help, I will try it out!

[joojaa]

Enable quat interpolation for the curves. Thing is matrices and quats calculate slices of a 360 degree thing eulers don't. And the reason you don't use eulers at all times is that they cat interpolate corretly at all times. However if you wish to interpolate quats in euler space you need to at least change the rotation to correct slice of 360 degrees something quats are blind off (if you rotate around one axis for 720 you get the same quat as 360 and 0 but eulers can see difference betrween values here). The reasom you DO use eulers is that artist can adjust curves better on euler angles curves something that quat data is totally blind to.

how to set quat interpolation on see the manual entry Set rotation interpolation for curves thisway the interpolation will be shortest path (you still need to set quats as eulers, AND you need to allways key the 3 values concurently), so you dont need th 360 addition if you have less than 180 steps.

[jeffm3]

Thanks, but are you saying this can only be done at the GUI level?

Is there no way to setup quaternion interpolation for curves through the API?

I wish I could just give Maya quaternions, because I'm still having trouble with sending it
euler angles. Fixing the euler angles seemed to worked in some places, but I'm still getting
bad rotations. This is terrible.

[joojaa]

No you can set them via the api too (you just have to understand maya node internal workings and for that you need to read the minuscule details in node reference). And yes you can set the values in quats directly but then you'd have to step trough time.

each transform has a rotationInterpolation attribute change that.

But understanding quats vs eulers is important here! (a euler cant really interpolate over its own pole it looks weird) unfortunately quats only interpolate well lineary. Thing is if you work in api then your supposed to know about internals.

Ps if quats were easy to handle wed all have ditched eulers long ago, but they arent. For one you cant edit their tangents because it makes absolutely no sense. A deecent animator would get the jiibies because of this, because he now has to set a gzillion intermediary keys. However quats are good if you need to interpolate two values together, just hard to key properly because the graphs of quats make less than no sense (most humans cant predict anything form quats because of their construct by looking at the graph, because most of us have a problem with extradimenssional spaces).

[jeffm3]

Thanks, choosing that GUI option fixed all of my animation. However, I'm getting errors returned trying
to do it in code.

After creating my curve and add its rotation keys, I call this MEL command:
MStatus status;
MStringArray result;
status = MGlobal::executeCommand( "rotationInterpolation -convert quaternion mybone_rotateX", result );

But status returns:
"(kFailure): Unexpected Internal Failure"

I tried setting this attribute using API functions:
int roi = 2;
MObject newJoint; // already created above
MFnDependencyNode fnNode(newJoint);
fnNode.findPlug( "rotationInterpolation" ).setValue( roi );

That didn't seem to work.

Tried it again this way:
MFnAnimCurve animCurve; // already created above
animCurve.findPlug( "rotationInterpolation" ).setValue( roi );

Didn't work either.

How do you set the "rotationInterpolation" attribute?

Yes, I'm still learning how the Maya API works, btw.

[jeffm3]

Even the Script Editor is returning the same error. I type in the command twice, and it says
it's already set. So, even though it returned an error, it changed the interpolation type.
Do you get an error using this command?

rotationInterpolation -convert quaternion root_rotateX;
// Result:3//

rotationInterpolation -convert quaternion root_rotateX;
// Warning: Rotation interpolation is already set to that type. Skipping: root_rotateX //
// Result:0//

[joojaa]

yes but maya does not actually interpolate like that unless you have synchronized pairs of rotates on all rotate channels in place, on the entire curve range.