Step 4 - Define events

Events are commonly used to identify key points in the motion captured data such as foot contact or foot off when the subject is walking, or any other event type which can be used, for example, to time normalize the kinematic data.

ProCalc automatically reads the standard Vicon events from the input .c3d file – left/right/general foot contact/foot off/general.

Additionally, you can choose to add more events using ProCalc’s event generation schemes.

To create an event scheme:

1. At the top of ProCalc’s main window, click on the Events tab, click the Create button to create a new event scheme and as before, name it Test and press Enter.

2. As for the other schemes, click the Add button to add a new event.

3. Note that the window now looks similar to the following:

   

4. Your first choice is whether to add a custom event or one of the Vicon standard events. For this tutorial, we will create a couple of new custom events that define the middle of a walking trial’s swing phase. We define this as the point where the swinging foot’s position in the direction of travel first moves ahead of the stance foot.
   First, make sure that the chosen event type is General Custom Event, then enter LeftMidSwing as the event’s name.
5. From the drop-down menus next to the Event triggered by label, select Length, and then the LeftFoot_v_RightFoot variable that we defined previously. Then, we choose to add the event at the Threshold crossing of value 0 (the default) absolute value in the Direction Up. This means that whenever the variable LeftFoot_v_RightFoot crosses from being negative to being positive, we add a LeftMidSwing event.
   You can also add more conditions for the event generation:
   
   • The event must stay over/under the threshold for a certain number of milliseconds. This condition helps avoid a double identification if there’s a little noise just around the threshold value. In our case, we know that the left foot will stay in front of the right foot until the right foot comes swinging back, which, even for fast walking, will take half a second or so, so we could specify 200ms for this parameter.
   • If you’d like the new events only to be added between events that are already present, you also have the option of telling ProCalc only to add event between two other events.
   • You can also add a dependency on another event, requiring this to be below, above, equal to or not equal to another variable. This could, for example, be useful if you’re trying to define a foot contact events, and in order to reduce the possibility of false positives you might require the heel marker’s vertical position to be below a certain value.
   Note that the events generated by the event definition currently chosen in ProCalc’s event list are visualized on the time bar as yellow bars. The event times, in seconds, are also output to the log.
   Also note that you have several other options for the condition to define the event. You can choose to define it at a variable’s maximum or minimum value, or you can define the threshold as a relative rather than absolute value, either as a percentage of the variable’s range, maximum or minimum value.