Joint Rotation

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:

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.

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.