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If required, you can change the properties for each of the operations that are included in the Plug-in Gait Dynamic pipeline. You can also run them individually, and/or run other operations at this stage too. To help you understand the different operations typically run on Plug-in Gait movement trials and the options available, each operation is described in the following topics, together with the Delete Unlabeled Trajectories pipeline operation, which you may also find useful:
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| Tip When you are familiar with these operations, you can run all of the data processing in a single step by creating a custom pipeline and adding all the operations described in this section to it, as explained in Create a pipeline. When you create your new pipeline, be sure to include the operations in the above order. |
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This pipeline operation filters the data using the Woltring filter to ensure smooth trajectories for calculating kinetics. This routine is based on a fifth-order spline-interpolating function (for details on this function and its filtering algorithms, see Plug-in Gait references).
In the Properties pane for this operation, you can specify these settings:
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| Property | Description |
|---|---|
| First Frame | First frame in which events are detected |
| Last Frame | Last frame in which events are detected |
| Only after existing | If a force plate is used and you select this option, Vicon Nexus automatically correlates force plate data events from the time of the first strike on the force plate and forward. If you do not select this option, Vicon Nexus automatically correlates events both forward and backward from the first force plate strike. If a force plate is not used, you can still select this option, but you must make a thorough visual check of the events placed. |
| Correlation Method (Advanced property) | Enables you to choose the correlation method to automatically place events at the correct location in the time bar: Legacy, Least Squares or Pearson Coefficient (see Correlation Method parameters in the Vicon Nexus Reference Guide). |
| Marker (Left and Right) | Enables you to change the marker used for correlation if necessary. |
| Component (Left and Right) | For walking trials, leave the Left and Right values at the default value (Z). For running and other motor tasks, change as appropriate. |
| Derivative (Left and Right) | For walking trials, leave the Left and Right values at the default value (Position). For running and other motor tasks, change as appropriate. |
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| Property | Description |
|---|---|
| First Frame | First frame on which the operation is run |
| Last Frame | Last frame on which the operation is run |
| Marker diameter (mm) | Ensure the specified value corresponds to the diameter of the markers used (assuming they are applied directly to the skin surface). Note: If your marker has a base, to calculate the correct value, double the base width and add it to your marker diameter in mm. |
| Reaction reference frame | Determines which reference frame is used for reporting joint moments: Proximal segment: Reports all moments in the reference frame of the proximal segment. Distal segment: Reports all moments in the reference frame of the distal segment (for example, the tibia segment for the knee joint). Global frame: Reports the moment vector relative to the laboratory coordinate system. |
| Power Output | How Plug-in Gait is to output the power data: Standard: The joint power expressed as a single number (scalar). Individual Contributions from XYZ: The joint power expressed as individual X, Y, and Z planes in the segment's coordinate system |
| Anterior Thorax Tilt is Positive | Select this option to specify that the anterior thorax tilt is positive. Clear this option to specify that the anterior thorax tilt is negative. |
| Output Joint Centers | Select this option to visualize the joint centers that are calculated by Plug-in Gait. |
| Output Segment Centers of Mass | Select this option to visualize the center of mass of each segment that is calculated by Plug-in Gait. |
| Allow cross-plate strikes | Select this option when a foot may be in contact with more than one force plate simultaneously; for example, the heel may land on the far side of one plate and then the toes roll onto the near edge of the subsequent plate. If you select this option, reactions from the two plates are combined during processing, with the plate that is struck first being considered the primary. The forces reported by each plate are added together; the moments are also combined by referring the moment from the secondary plate back to the origin of the primary plate. In effect, the two plates are treated as a single force plate with the same origin as the primary plate. For more information, see Cross-plate foot strikes. Although every effort has been made to ensure the mathematical combination of forces and moments between two plates is correct, it is the responsibility of the operator / analyst to review the outcomes produced by this process and ensure they are correct. Use of this option in clinical assessments is strictly at the discretion of the operator/analyst. |
| Radius of Gyration: Pelvis and Thorax | The default radius of gyration for the specified segments. The number is scaled to the length of the segment. The Plug-in Gait default setting (0.31) means that the radius of gyration is 31 percent of the segment length. Only change this setting if you are sure that the default value is incorrect. |
| Version | Plug-in Gait version number. |
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Cross-plate foot strikes
To perform an inverse reaction calculation from a foot strike, forces and moments recorded by a force plate must:
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In some instances, a foot may be in contact with more than one force plate simultaneously; for example, the heel may land on the far side of one plate and then the toes roll onto the near edge of the subsequent plate.
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Dynamic Plug-in Gait includes an Advanced option to permit calculations based on these cross-plate strikes.
Reactions from the two plates are combined during processing, with the plate that is struck first being considered the primary. The forces reported by each plate are added together; the moments are also combined by referring the moment from the secondary plate back to the origin of the primary plate. In effect, the two plates are treated as a single force plate with the same origin as the primary plate.
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You may also set the foot strike manually (see Add events to trials and also Automatically assess foot strikes).
Note that the existing restriction that there must be only a single foot in contact with any given force plate still applies.
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This pipeline operation exports the current state of the processed data to a .c3d file. You can then import the data into other software for further processing or report generation. For example, in Vicon Polygon you can visualize the trajectories, kinematic model elements, and kinetics data. If you manually import the corresponding .vst file into Polygon, it also visualizes the bones. For more information, see Configure the Export C3D operation.