BUG: Fix Computation of Interaction Transform Used in PositionProp | ⚠️ Changes removed from master

[jcfr]

⚠️ Changes originally introduced through this pull-request have been removed from master by force pushing. Corresponding changes are superseded by #141 ⚠️

Rational:

• BUG: Fix Computation of Interaction Transform Used in PositionProp | ⚠️ Changes removed from master #139 (comment)

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This commit fixes the incorrect and unnecessary conversion from axis-angle to quaternion inadvertently introduced in 503ef1d ("ENH: Add VR interactor style class for transforming objects in MRML", 2018-08-31).

The additional conversion, introduced in the mentioned commit, was redundant since the event orientations (internally set using vtkVRRenderWindowInteractor::ConvertPoseToWorldCoordinates, itself introduced in Kitware/VTK@803d3a327d, "ENH: Use pose matrices instead of camera parameters for VR controllers", 2018-09-25) are already in quaternion format.

The redundant conversion was leading to an invalid transformation of the selected object.

Reported by @LucasGandel and @sankhesh

[jcfr]

I may have missing something as inspecting code like the one in vtkInteractorStyle3D::Dolly3D, there is:

  vtkEventDataDevice3D* edd = static_cast<vtkEventDataDevice3D*>(ed);
  const double* wori = edd->GetWorldOrientation();

  // move HMD world in the direction of the controller
  vtkQuaternion<double> q1;
  q1.SetRotationAngleAndAxis(vtkMath::RadiansFromDegrees(wori[0]), wori[1], wori[2], wori[3]);

I am re-evaluating and I will likely force push to revert, and create a following-up topic.

[jcfr]

Analysis

During my initial review of the code associated with vtkVRRenderWindowInteractor::ConvertPoseToWorldCoordinates, I got confused with the docstring mentioning \param wxyz Output world orientation quaternion¹ which primed me during my visual inspection of vtkVRRenderWindowInteractor::ConvertPoseToWorldCoordinates source code. As I saw Matrix3x3ToQuaternion, I stopped visually parsing the code and went one with the conclusion that the orientation was a quaternion.

ConvertPoseToWorldCoordinates docstring	Matrix3x3ToQuaternion

However, upon further consideration, I realized that the orientation is effectively² converted to an angle-axis representation. This conversion aligns with VTK's typical internal handling of orientation.

cc: @allemangD

Footnotes

1. https://github.com/Kitware/VTK/blob/2579c39f26d6800cea2b5b0ca7b094dd22bc7bf9/Rendering/VR/vtkVRRenderWindowInteractor.h#L97-L105 ↩

2. https://github.com/Kitware/VTK/blob/2579c39f26d6800cea2b5b0ca7b094dd22bc7bf9/Rendering/VR/vtkVRRenderWindowInteractor.cxx#L258-L274 ↩