Rotation Interpolation Problem

[uiron]

interpolating rotations with orient constrains are giving me headaches. here's an example

two locators in the scene. first one rotated [0,180.1,0], another one [0,-179.9,0] . two almost identical orientations of an object.

how can i setup a third locator to CORRECTLY interpolate between these two? the orient constrain obviously not doing the job, saying that interpolation mode "shortest" will give a SLERP interpolation between these two? guess what, it results in [180,0.1,0], which means a flipped X and Y axis.

i'm really tired using workarounds with position and aim constrains when it comes to interpolating rotations. i don't even ask for extreme interpolations between very different rotations. but when i can actually see that two orientations in space almost line up, and the so-called shortest interpolation gives flips - i want to raise hell on earth, seriously.

[gmask]

my first impression is that this is essentially a mathematical anomaly like gimbal lock that is not easily resolved.

Have you tried using an orientate constraint per axis?

[uiron]

ok so i went so far that i created plugin from scratch and SLERP'ed two quaternions out of euler values of [0,180.1,0] and [0,-179.9,0], and guess what, slerp returns just the same bugged result as rotation constraint - [180,0.1,0].

the funny thing is, this bugs out just in range of aprox. one euler angle, that is, result of 180::-179.0 is correct.

one very odd thing that helped was converting ALL euler angle values to 0..360 range first. but then the "one angle range bug" happened at zero, that is, 0 vs. -0.5. it looks like maya's internal MQuaternion.slerp() is not very accurate, or there is something i don't know.

ideas, anybody?

[uiron]

I guess i found the problem. i changed my plugin to take input rotations as raw WorldTransform matrices and get Quaternion rotation values from those rather than converting from euler angles (MEulerRotation.asQuaternion()).

so now interpolated rotation is calculated from:

• inputTransform1, inputTransform2 : transform matrices of two objects to interpolate between;
• parentTransform: parent transform matrix of a node that's gonna receive interpolated rotation
• bias: float 0..1 , defines interpolation value (0.5 - rotation divided equaly, 0 - matches first rotation, 1 - matches second rotation)

worked like a charm, no flips except ofc the gimbal one.

EulerRotation -> Quaternion conversion bugged in API?