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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. }}
