Incorrect rotation using driver or constraint #79118

New Issue

Roman · 2020-07-20T16:43:04+02:00

Roman commented

2020-07-20 16:43:04 +02:00

System Information
Operating system: Windows-7-6.1.7601-SP1 64 Bits
Graphics card: GeForce GTX 750 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.13

Blender Version
2.79, 2.80, 2.81, 2.82, 2.83

Short description of error

Bone "target" is animated on y-axis.
"Target" turned close to gimbal lock gives the wrong result for Transformation constraint, Copy Rotation constraint, Driver.
Using the driver, you can see how the radian (degrees) value jumps and does not match the value of the target object.
Only using the driver via copy data path creates the correct result.

rotation.blend

rotation_.mp4

**System Information** Operating system: Windows-7-6.1.7601-SP1 64 Bits Graphics card: GeForce GTX 750 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 388.13 **Blender Version** 2.79, 2.80, 2.81, 2.82, 2.83 **Short description of error** Bone "target" is animated on y-axis. "Target" turned close to gimbal lock gives the wrong result for Transformation constraint, Copy Rotation constraint, Driver. Using the driver, you can see how the radian (degrees) value jumps and does not match the value of the target object. Only using the driver via copy data path creates the correct result. [rotation.blend](https://archive.blender.org/developer/F8709086/rotation.blend) [rotation_.mp4](https://archive.blender.org/developer/F8716807/rotation_.mp4)

Roman commented

2020-07-20 16:43:04 +02:00

Added subscriber: @roman-13

blender-admin commented

2020-07-20 16:43:04 +02:00

#102679 was marked as duplicate of this issue

Roman changed title from ~~Wrong rotation Driver and Constraints~~ to Incorrect rotation using driver or constraint

2020-07-21 10:57:54 +02:00

Richard Antalik commented

2020-07-22 06:49:01 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Sybren A. Stüvel commented

2020-07-23 18:15:12 +02:00

Added subscriber: @dr.sybren

Sybren A. Stüvel commented

2020-07-23 18:15:12 +02:00

@roman-13 In the future, please don't use GIF for videos. What is called a "gif" on modern websites is usually video file. H.264 in an MP4 container works fine for browsers, and is of higher image quality & smaller file size than GIF. It's nice to have a demo video that shows the issue, but modern video codecs are way better at that ;-)

Roman commented

2020-07-23 22:41:56 +02:00

This comment was removed by @roman-13

*This comment was removed by @roman-13*

Roman commented

2020-07-23 22:54:57 +02:00

@dr.sybren Ok. Is that better?
rotation_.mp4

@dr.sybren Ok. Is that better? [rotation_.mp4](https://archive.blender.org/developer/F8716807/rotation_.mp4)

Sybren A. Stüvel commented

2020-07-27 11:24:11 +02:00

@roman-13 much, thanks!

Sybren A. Stüvel commented

2020-08-06 14:00:52 +02:00

I did some digging, and it seems to be caused by limitations of Euler angles.

Try this in Blender's Python Console:

>>> e26 = Euler((0.783653, 2.10281, 4.45932), 'YZX')
>>> e26.to_matrix().to_euler('YZX')

Euler((0.7836530208587646, 2.1028099060058594, -1.8238651752471924), 'YZX')

>>> e27 = Euler((0.783653, 2.18692, 4.45932), 'YZX')
>>> e27.to_matrix().to_euler('YZX')

Euler((-2.3579397201538086, -0.954672634601593, -1.3177274465560913), 'YZX')

Here e26 and e27 are the Euler angles of the target bone on frames 26 (before the jump in orientation) and 27 (after the jump in orientation) in radians. Converting them to a matrix and then back to Euler angles shows the issue: a small change in Y-angle results in a big change in the result. The same happens when converting from Eulers to quaternions and back.

The difference between the various approaches is that the "Copy Data Path" approach literally takes the Y euler rotation as-is. All the others first convert the rotation to a matrix, convert that matrix to whatever space is desired, convert it to Euler angles again, and and then take the value from that.

It could be argued that there could be some shortcuts in this process, to avoid unnecessary conversions. However, this would only apply to very specific cases (only local space, and no change in the order of angle evaluation), and could thus cause confusion in other areas. It could also break existing files, unless yet more options are added.

I did some digging, and it seems to be caused by limitations of Euler angles. Try this in Blender's Python Console: ``` >>> e26 = Euler((0.783653, 2.10281, 4.45932), 'YZX') >>> e26.to_matrix().to_euler('YZX') Euler((0.7836530208587646, 2.1028099060058594, -1.8238651752471924), 'YZX') >>> e27 = Euler((0.783653, 2.18692, 4.45932), 'YZX') >>> e27.to_matrix().to_euler('YZX') Euler((-2.3579397201538086, -0.954672634601593, -1.3177274465560913), 'YZX') ``` Here `e26` and `e27` are the Euler angles of the target bone on frames 26 (before the jump in orientation) and 27 (after the jump in orientation) in radians. Converting them to a matrix and then back to Euler angles shows the issue: a small change in Y-angle results in a big change in the result. The same happens when converting from Eulers to quaternions and back. The difference between the various approaches is that the "Copy Data Path" approach literally takes the Y euler rotation as-is. All the others first convert the rotation to a matrix, convert that matrix to whatever space is desired, convert it to Euler angles again, and and then take the value from that. It could be argued that there could be some shortcuts in this process, to avoid unnecessary conversions. However, this would only apply to very specific cases (only local space, and no change in the order of angle evaluation), and could thus cause confusion in other areas. It could also break existing files, unless yet more options are added.

Roman commented

2020-08-06 16:19:22 +02:00

I found a discrepancy. I know the Y axis rotates in local coordinates, but I animated the X axis and for some reason the bone rotates with a constant in world space coordinate.

rotation_X.mp4
At a certain angle of rotation, Flip rotation also appears
flip_Z.mp4

I found a discrepancy. I know the Y axis rotates in local coordinates, but I animated the X axis and for some reason the bone rotates with a constant in world space coordinate. [rotation_X.mp4](https://archive.blender.org/developer/F8752375/rotation_X.mp4) At a certain angle of rotation, Flip rotation also appears [flip_Z.mp4](https://archive.blender.org/developer/F8752376/flip_Z.mp4)

Sybren A. Stüvel commented

2020-08-13 10:19:18 +02:00

That just looks like another gimbal lock to me.

I'm marking this as known issue as it seems to be a side-effect of how Blender handles space transformations, and not a bug in the implementation. As I said before, it might be possible to implement some shortcuts in the space conversion functions so that the conversion to matrix and back is avoided, but this requires very careful planning in order to not break existing files.

That just looks like another gimbal lock to me. I'm marking this as known issue as it seems to be a side-effect of how Blender handles space transformations, and not a bug in the implementation. As I said before, it might be possible to implement some shortcuts in the space conversion functions so that the conversion to matrix and back is avoided, but this requires very careful planning in order to not break existing files.

Sybren A. Stüvel commented

2022-11-29 12:15:34 +01:00

Added subscribers: @candreacchio, @ChrisLend

Philipp Oeser removed the

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Incorrect rotation using driver or constraint #79118