Triggers
ISAT User's Guide Table of Contents
Contents
Triggers
Behavior
Triggers are flexible coordinators that allow the development of simple or complicated scenarios. Simply put, triggers are predicate-action evaluated at runtime. In other words, if condition A is currently true, then perform action B. The predicates dictate conditions that, once satisfied, cause a variety of actions to take place. At runtime, triggers continuously evaluate their predicate conditions and, if satisfied, perform the actions.
There are several types of triggers. Each type is characterized by the conditions that can cause it to fire. Each trigger may then have a number of actions, such as “Create New Element”, “Start Data Reduction”, and so on.
Terminology
Several terms are used to describe concepts associated with triggers. These are described here.
| Firing | Firing refers to performing the actions associated with a trigger. |
| Target Set | The Target Set is a set of scenario elements that the trigger will act upon when it fires. For example, if a trigger is supposed to delete some scenario elements, then the Target Set would include the actual scenario elements that would be deleted. |
| Instigator Set | The Instigator Set is the set of elements whose direct action caused the trigger to fire. For example, if a trigger fires when a vehicle crosses a checkpoint on the road network, the Instigator Set would be the actual scenario element that causes the trigger firing by crossing the checkpoint. |
Uniform Parameters
Although triggers have no visual representation in the virtual environment (i.e., the simulator driver has no visible indicator that triggers exist), they are placed in fixed locations. Associating a location with a trigger allows use of the standard scenario element parameter Activation Radius.
Furthermore, all triggers have an Activation Delay and Lifetime parameter. For a detailed description of these parameters, see Section 3.17.
In addition to these scenario element global parameters, all trigger types share additional input parameters as follows.
One Shot
This is a binary input parameter. If set, the trigger will delete itself after firing once. If not set, the trigger will remain in the simulation after firing. The default value for this parameter is cleared.
Fire Delay
This parameter specifies the interval between the time when all conditions are satisfied and the time when the trigger fires. The default value of this parameter is 0, meaning that firing will happen immediately after the conditions are satisfied.
Denounce
This parameter specifies the minimum time that must elapse between successive firings of the same trigger. This parameter is useful for triggers whose conditions remain true continuously after some point in the simulation. In such a case, a trigger would fire continuously (i.e., once at each iteration of the scenario control software), which may or may not be desirable. The default value for this parameter is 0, indicating that as long as the conditions are satisfied; a trigger will fire once per iteration.
Priority
The priority setting controls the order the triggers are evaluated in. A high priority trigger would be evaluated before a low priority trigger. This is useful when there is interdependence between triggers. For example if you have a road pad trigger that sets a variable called “FireAlertSystem”, and you had an expression trigger that looked for the condition where “FireAlertSystem” was greater than 0. If the road pad trigger is set to a “high” priority, and the expression trigger is set to a low priority we can guarantee that the expression trigger will fire in the same frame as when the road pad trigger fires.
