Help me create a user case diagram based of this:

Use case title: View real-time information about location and availability of ambulance crews

Primary actor: Dispatcher

Level: User goal

Stakeholders: Dispatcher, ambulance crews, patients

Precondition: The ambulance emergency response system is operational, and ambulance crews are equipped with location and availability tracking devices.

Minimal guarantee: The dispatcher can view real-time information about the location and availability of ambulance crews.

Success guarantee: The dispatcher can make informed decisions about which ambulance crew to assign to a case based on their proximity and availability.

Trigger: The dispatcher needs to assign an ambulance crew to a case.

Main success scenario:

The dispatcher accesses the ambulance crew location and availability system.

The system displays the real-time location and availability of all ambulance crews.

The dispatcher selects an available ambulance crew that is closest to the location of the case.

The dispatcher assigns the selected ambulance crew to the case.

Extensions:

If the location and availability system is down, the dispatcher relies on other means of communication, such as phone or radio, to determine the location and availability of ambulance crews.

If there are no available ambulance crews nearby, the dispatcher requests availability from other crews or reassigns another crew from a lower priority case.