====== Joint Rotation ======

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A joint angle can be represented as a 3x3 rotation matrix that describes the transformation between two coordinate systems.

A Model based item describing the knee angle as a rotation matrix is:

{{:JointRotationDlg.jpg}}

**Compute_Model_Based_Data**\\
/RESULT_NAME=RKNEE_ANGLE\\
/FUNCTION=JOINT_ROTATION\\
/SEGMENT=RSK\\
/REFERENCE_SEGMENT=RTH\\
/RESOLUTION_COORDINATE_SYSTEM=\\
! /USE_CARDAN_SEQUENCE=FALSE\\
! /NORMALIZATION=FALSE\\
! /NORMALIZATION_METHOD=\\
! /NORMALIZATION_METRIC=\\
! /NEGATEX=FALSE\\
! /NEGATEY=FALSE\\
! /NEGATEZ=FALSE\\
! /AXIS1=X\\
! /AXIS2=Y\\
! /AXIS3=Z\\
;

The command will return 9 columns of data for each point in time. Each row represents a position in the 3x3 matrix.

{{:JointRotationMatrix.png}}

**NOTE:** If looking at the signal in the Data Viewer, the columns will be numbered 0 through 8. When accessing the columns using the Evaluate_Expression command, the columns can be accessed as 1 through 9. For this reason, the image above shows numbers 1 through 9. It is always important to pay attention when a signal or command is 0 or 1 based.