The callback function passed here is called whenever the view is changed by the user within the sphere view. User-changed views happen when the user adjusts pan or tilt with their mouse, or when they zoom in or out.
callback (function): A callback function to execute. It will be passed an object with the following properties:
azimuthAngle (number): The pan after the view change
polarAngle (number): The tilt after the view change
eventName (string): The name of the view change event. The possibilities are:
"controlstart": When the user starts to control the camera via mouse / touches
"control": When the user controls the camera (dragging)
"controlend": When the user ends to control the camera
"update": When the camera position is updated
"wake": When the camera start moving
"sleep": When the camera end moving
zoom (number): The new zoom level after the view change. See sendData for how to set the zoom programmatically, and getData for reading the current zoom level outside of events.