Table of Contents
Metric Signal Values in Sequence
Overview
The metric command Signal Values in Sequence can be used to compute the value of a signal at several events within a sequence, like at heel and toe strikes within a gait sequence. It can be found in the Pipeline Workshop under Metric.
Pipeline Command
The syntax for the function is as follows:
Metric_Signal_Values_In_Sequence ! /RESULT_METRIC_FOLDER=PROCESSED /RESULT_METRIC_NAME= /EXPRESSION= ! /PERCENT_LIST= ! /TIME_OFFSET_LIST= ! /FRAME_OFFSET_LIST= ! /EVENT_LIST= ! /USE_FRAMES_TYPE=1 ! /SEQUENCE_INSTANCE=0 ! /EVENT_SEQUENCE= ! /EXCLUDE_EVENTS= ! /GENERATE_MEAN_AND_STDDEV=TRUE ! /RETAIN_NO_DATA_VALUES=TRUE ;
Command Parameters
The following table shows the command parameters seen above and their descriptions:
| RESULT_METRIC_FOLDER | The name of the result signal folder |
| RESULT_METRIC_NAME | The name of the result signal |
| EXPRESSION | Location of original signal (example: 'LINK_MODEL_BASED::ORIGINAL::LEFT_KNEE_ANGLE') |
| PERCENT_LIST | A percentage offset relative to each event in the defined sequence |
| TIME_OFFSET_LIST | A time offset relative to each event in the defined sequence |
| FRAME_OFFSET_LIST | A frame offset relative to each event in the defined sequence |
| EVENT_LIST | The events at which the signal will be computed within the sequence |
| USE_FRAMES_TYPE | Use point frames(1), data frames(2), or interpolate between frames(3) |
| SEQUENCE_INSTANCE | Specify which instance of the sequence to compute 0 = All |
| EVENT_SEQUENCE | A list of events (separated by “+” signs). For example, LHS+RTO |
| EXCLUDE_EVENTS | This Event Sequence must not be during the sequence requested. For example, LTO_RHS |
| GENERATE_MEAN_AND_STDDEV | (True or False) Generate the mean and standard deviation for all of the metrics created |
| RETAIN_NO_DATA_VALUES | (True or False) If the result is no_data, retain the value. |
Dialog
The command can be edited in a text editor or in a dialog form. To edit in the dialog pop up form either click on the Edit button in the pipeline workshop or double-click on the pipeline command. The dialog is shown below.
The dialog box allows you to assign values to the command parameters outlined above.
At Event: The at event command is used to dictate at which event the signal will be computed.
Example: joint angle during cycle
Here Metric Signal Values in Sequence is used to compute the left knee angle at 25% of the gait cycle
NOTE: The Metric_Signal_Values_In_Sequence command may be edited through the text editor or the GUI.
Metric_Signal_Values_In_Sequence /RESULT_METRIC_NAME=LEFT_KNEE_ANGLE_25percent ! /RESULT_METRIC_FOLDER=PROCESSED /EXPRESSION=LINK_MODEL_BASED::ORIGINAL::LEFT_KNEE_ANGLE /PERCENT_LIST=25 ! /TIME_OFFSET_LIST= /USE_FRAMES_TYPE=2 ! /SEQUENCE_INSTANCE=0 /EVENT_SEQUENCE=LHS+LHS ! /EXCLUDE_EVENTS= ! /GENERATE_MEAN_AND_STDDEV=TRUE ! /APPEND_TO_EXISTING_VALUES=FALSE ! /RETAIN_NO_DATA_VALUES=TRUE ;
The resulting metrics can be found in the METRIC:PROCESSED folder:
Example: Comparing Joint Moments in Stance
The behaviour of lower body joints during stance (while the foot is on the ground) provides valuable insight into gait mechanics as it represents the portion of the stride in which external forces are acting on the limb. Here we will use a series of commands, including Automatic Gait Events and Metric Signal Values in Sequence to compute the ankle moment at the different points between each heel strike and toe off.
First, key gait events must be defined that will be used to build the command:
Automatic_Gait_Events ! /FRAME_WINDOW=8 ! /USE_TPR=TRUE ! /TPR_EVENT_INSTANCE=1 ;
Next, Metric Signal Values in Sequence is used to define the stance sequence for the right foot (RHS to RTO) and find the right ankle moment at 3 points between those events:
Metric_Signal_Values_In_Sequence ! /RESULT_METRIC_FOLDER=PROCESSED /RESULT_METRIC_NAME=RAnkle_Moment_Stance /EXPRESSION=LINK_MODEL_BASED::ORIGINAL::RAnkleMoment /PERCENT_LIST=25,50,75 ! /TIME_OFFSET_LIST= ! /FRAME_OFFSET_LIST= ! /EVENT_LIST= /USE_FRAMES_TYPE=2 ! /SEQUENCE_INSTANCE=0 /EVENT_SEQUENCE=RHS+RTO ! /EXCLUDE_EVENTS= ! /GENERATE_MEAN_AND_STDDEV=TRUE /RETAIN_NO_DATA_VALUES=FALSE ;
The resulting metric contains the x, y, and z moments at 25, 50, and 75 percent of the stance phase for each right foot strike.
