Events are used to identify specific time points in a trial where “something interesting” occurs. The standard Vicon events (Left/Right/General Foot Contact/Foot Off/General) are available, as are custom events where you are free to name the event whatever you like. The relevant controls are:
To define an event:
- On the Events tab, click an existing event to edit, or click Add to create a new one.
- Select the event type from the drop-down list. The nine standard Vicon Nexus events are available, but you can also create a custom event. If so, you also get the option of naming the event whatever you want.
- Select the variable type and the variable you want to use as the trigger. This could be a trajectory or analog data variable from the trial, or it could be one of your own calculated trials.
- Select when the event should be generated. You have three options:
- Generate the event when the variable attains its maximum value.
- Generate the event when the variable attains its minimum value.
- Generate the event when the variable crosses a threshold. The threshold can be defined as either an absolute value (for example “15 degrees”), or a relative value. Furthermore, the relative value can be taken as a percentage of the variable’s range, maximum or minimum value, or even the range of just the current cycle. See below for a description on how to define cycles.
- To avoid false positives caused by the variable’s value hovering around a threshold, you can also specify that the threshold has to be crossed for a minimum number of milliseconds. If you do this, and the variable’s value happens to creep above the threshold before dropping below and back above again, only the last threshold crossing is identified.
- You can add a dependency on a separate variable by selecting the Only when variable check box and completing the drop-downs. For example, an algorithm for determining foot contact may use the speed of a marker’s Z component, but also require the marker’s Z coordinate to be below a certain threshold. The second requirement can be specified using the Only when variable function.
- You can also use the Only between Events check box to create events only when the threshold/minimum/maximum condition is reached between two other events. For example, this may be useful if you want to identify an event when the peak angle during swing has been reached. In this case, you’d choose to only add the event between the Foot off and Foot contact events. In this case, the maximum is also evaluated for each cycle separately, rather than for the trial as a whole.
- When you are finished, remember to save the scheme.