Graph view

The Graph view enables you to view various values of one or more selected items (such as the x, y, and z components of a marker trajectory) against each other or against time, or analog data from any supported force plates or EMG devices.

You can view graphs of motion data live in real time or from a previously saved reconstructed and labeled trial.

In addition to the standard buttons (see View pane), the Graph view contains the following controls.

Graph view pane toolbar

Manage the display of graph data in the view pane with the following controls at the top of the view pane. The Graph view pane toolbar leads you left to right through the normal flow of operations required to plot a graph for the selected elements

• Graph type drop-down list
  Select the type of graph to be displayed from the categories in this drop-down list. (Graph types that are not available for the data currently selected in the System Resources pane are dimmed.) See Graph type options.)

  

• Differentiate the graph button Specify, for the currently displayed graph, the current variable, its first derivative (velocity or angular velocity), or its second derivative (acceleration or angular acceleration) by selecting the desired options from this drop-down list:

  • x (none)
  • x' (velocity)
  • x" (acceleration)
  A graph of a trajectory will have X, Y, and Z axes, but when differentiated to x' (velocity), the axes will change to X', Y', and Z' axes.

  Tip: You can then use the Add Monitor button to provide real-time bio-feedback on differentiated as well as positional data. For more information, see Using monitors.

• Choose the components of the graph button Specify the components of the selected graph type to be plotted in the active Graph view by selecting the desired options from this drop-down list (only components that you have selected for Graph view are available).
  This option enables you to focus on a component of particular interest, which occupies more of the workspace. When multiple components are plotted, each is always shown on a separate axis, and the components shown are applied to all channels visible in the workspace. The number of vertically stacked graphs displayed in the workspace depends on the number of options selected for graph view, and from those, the number selected from this list.

• Legend button Display a legend for the current graph listing the color for each trace plotted, the subject (if multiple subjects are loaded), and the name of each element being plotted in that trace. To display a temporary tooltip with this information, hovering the mouse pointer over the button. To open a separate splitter pane to permanently display the legend to the right of the graph view, click the button.

• Choose the rotation order button If you select a segment in the Subjects Resources pane, you can select Global Angle from the Graph type drop-down list. This enables the Choose the rotation order button. Clicking on the Rotation Order button lists the angle convention choices of Helical (default), XYZ, XZY, etc. This enables you to choose either a Helical or an Euler angle convention. The Euler angle convention has multiple rotation order conventions represented by XYZ, XZY, etc.

• Create a monitor button Add the selected graph component as a monitor entry in the Monitors communications pane.

• Scale the graph to fit (horizontal) button Zoom out the x-axis to show the complete range of the trace for the selected time period. This is useful if you have zoomed in a long way and now want to quickly see the entire graph again.

• Lock the horizontal graph axis button Lock the horizontal axis to prevent further rescaling of the axis once it is at a desired length of frames. This is useful if you want the horizontal axis range to stay the same.

• Scale the graph to fit (vertical) button Scale the y-axis so that all the data in selected traces for the currently visible x-axis is visible. If there are multiple components in the selected traces, they are all set to the same range, that is, the range required to show all the data in the component with the largest range.
  If Nexus is in Live mode, this button acts as a toggle, enabling you to leave this mode switched on or off. If on, when plotting live data, the y-axis is automatically scaled as the data changes so all traces are visible. Manually zooming switches the automatic mode off.

• Lock the vertical graph axis button Lock the vertical axis to prevent further rescaling of the axis once it is at a desired range. This is useful if you want the vertical axis range to stay the same.

• Scale the graph to fit (horizontal and vertical) button Scale the x and y axes simultaneously to fit the horizontal and vertical ranges of data.

• Lock / Unlock button (displayed with standard buttons on the right) Lock the current Graph view pane, so that it is effectively detached from the selection set and is not affected by any subsequent selections in other open view panes. This is useful for displaying elements in multiple Graph views.
  When the active clip changes, or when you switch from Live to Offline mode, the selection is automatically unlocked.

Graph view pane

View and manipulate graph data in the view pane below the view pane toolbar. For example, you can slide the displayed data along the axes or zoom in and out.

Graph type options

Devices
Displays graphs for the components of the analog signals from force plates or EMG devices. This is useful for examining analog device activity such as force plate strikes or EMG voltage output. You can also display graphs displaying units of mm/s2 of analog signals from an accelerometer device, which allows you to examine voltage output from an accelerometer device.

• Components: View force plate data such as Forces, Moments, and Center of Pressure, or to view Other Devices, such as EMG and Accelerometer data.
• Combined Forceplates: Enables you to view combined selected outputs from multiple force plates. For more information, see View combined output from multiple force plates in the Vicon Nexus User Guide.

Subjects

• Labeling: View labeling data for the current subject

Trajectories
Displays graphs for one or more marker trajectories selected, such as the global XYZ components of a marker, a marker's distance from the global origin, distance between two markers, angle between three markers, or a count of how many reconstructed markers are in any current frame of data.

• Components: View the X, Y, and Z coordinates of a marker selected in either the Subjects Resources pane or the 3D Perspective view.
• Distance From Origin: View the straight-line distance between the chosen point and the global origin. Plots the distance from the capture volume origin to each selected marker. This is useful for plotting velocity or acceleration of markers.
• Distance Between: View the straight-line distance between two markers selected in either the Subjects Resources pane or the 3D Perspective view.
• Distance Between (XYZ): View the global X, Y, and Z components of the distance between two markers selected in either the Subjects Resources pane or the 3D Perspective view. Plots the absolute distance (as a vector) between two selected markers. This is useful, for example, to see how the distance between two markers that are assumed to have a rigid relationship changes over time. This graph type calculates a separate component (X,Y,Z) distance between the two markers. It is only available when two markers are selected in the 3D Perspective view.
• Angle Between: Plots the angle between the two vectors formed by any three markers selected in either the Subjects Resources pane or from the 3D Perspective view pane. This is useful for seeing how the group of markers moves over time.
• Trajectory Count: View the number of markers (both labeled and unlabeled) currently reconstructed in the 3D Perspective view. Plots the total number of trajectories over time visible to the Vicon cameras (if streaming Live data in real time) or processed in trial (if viewing previously captured data in a file).

Model Outputs
Displays three graphs of the components of any output variables (such as Angles, Forces, Moments, Powers, or Bones) that have been calculated by Vicon Plug-in Gait for your model. This is useful for visually validating data produced by post-capture processing models without having to load the data into Polygon for full biomechanical analysis or reporting.

• Model Outputs: Select to view outputs from calculations run in post-capture pipeline.
• Difference Between: The difference between first and second selected model output in X, Y and Z (example: New Patient 1:LAnkleAngles - New Patient 1:RAnkleAngles)

Joints
Displays graphs of the components of selected joint kinematics, either three graphs for Euler angles or six graphs for a helical vector (as appropriate for the joint type). This is useful for displaying approximate joint angles between linked segments of the labeling template worn by your subject in real time. This type of graph can only be plotted for a subject that has been kinematically fitted (for example, one that has had the Kinematic Fit operation, found under Core Processing on the Pipeline Tools pane, run on it).

• Kinematics: Select to view kinematic angles between linked segments of the subject. (To see these angles, you must have performed kinematic fitting on labeled trajectories.)

Segments

• Global Angle The angle between the selected segment and the global origin in rotation (RX, RY, RZ) and translation (TX, TY, TZ).

Graph view usage tips

• When zooming into or out of graph data, the display of grid lines can be set to guide the eye toward the selected area of focus. Major grid lines remain at their normal weight, while any minor grid lines gradually fade. To obtain this behavior, in the Options dialog box (F7), select Graph and then ensure the Show Minor Grid Lines property is selected.
• The Graph view contains rulers and axes along the left and bottom edges and graph traces for the item being plotted. The contents of the axes of the Graph view depend on whether the system is in Live or Offline mode:
• Live The y-axis vertical ruler is on the right side of the graph and the x-axis horizontal ruler is below the graph. The y-axis represents the live frame, so is constantly updated in real time. The x-axis represents the time (in frames). It starts on the right side, which is labeled 0 (zero) and is labeled from right to left with decreasing negative values to reflect the number of frames away from the live frame. Because the current time is always zero, the Time Bar is not displayed at the bottom of the workspace.
• Offline The y-axis vertical ruler is on the left side of the graph and the x-axis horizontal ruler is below the graph. The rulers indicate the scale and the variable names that are being plotted and the horizontal and vertical axes are labeled to indicate the units of measurement used. The graph traces represent the actual data and are scaled to the current rulers. You can select elements to graph in the Resources pane or the 3D Perspective view.
  If the elements selected have more than one component, these components are shown on separate, vertically stacked axes sharing a common x-axis. You can select the components to be displayed from the Component Options list in the Graph view pane toolbar.
• You navigate in Graph view in the usual way, using the mouse. For example, to pan and zoom, click and hold the right mouse button and then drag the mouse up/down to zoom along the Y axis or drag left/right to zoom along the X axis. To pan the graph in any direction, hold the left and right mouse buttons down at the same time as you drag the mouse.
• When you select a data type in the System Resources pane (Trajectories, Model Outputs, Devices, or Joints), Nexus will attempt to intelligently update the Graph view type to match the data type you've selected.

To visualize data in a graph:

1. Either click the Go Live button or on the Data Management tab, double-click a processed data file (.c3d) file.

2. Select the elements to be graphed (eg markers, model outputs, force plates, etc) in any of the following ways:
   
   • In the Subjects Resources pane, expand the desired Subject node, expand the relevevant sub-node (eg Markers, Model Outputs, etc), and then select (CTRL+click to select multiple elements) one or more elements; or
   • In a 3D Perspective view pane, select one or more elements displayed in the view pane.
   The number of elements you select depends on the type of graph you wish to view.
3. From the view pane toolbar select Graph.
   If required, you can select additional elements to add to the Graph view pane. If you are viewing trajectories, each one is displayed in a different color trace. You can use the Legend button in the Graph view pane toolbar to identify the color trace used for each trajectory. If the trace for any additional elements is not visible, use the Fit Horizontally, Fit Vertically, or Fit Both Horizontally and Vertically buttons.
4. If you want to save a particular graph view (for example, specific trajectories that you have selected), save your configuration using theConfiguration menu button next to the View Type list on the Nexus toolbar.

You can visualize raw analog signals in a Graph view by selecting Show Raw from the device node context menu in the System Resources pane.

Graphing joint kinematics

1. Select the joints that are of interest.
2. From the Graph Type list in the Graph view pane toolbar, select the Kinematics option under the Joints section to plot the joint angles for the selected joints.
   Kinematic components for root segments include Tx, Ty, and Tz, accompanied by Rx, Ry, and Rz. These components can be further differentiated to also include Rx', Ry', Rz', Rx'', Ry'', Rz'', Tx', Ty', Tz', Tx'', Ty'', and Tz''. Designate the T's as translations and the R's as rotations between the two segments that the joint connects.
   Note: The ' and " designations are used to indicate velocity and acceleration, respectively.