All joystick types of control - Virtual Joystick, USB Joystick, and trackball mouse control, offer pan/tilt/zoom control with variable speed.
Your regulate the speed of the pan, tilt, and zoom movements by the movement of the computer mouse, joystick, or ball mouse relative to the center point of the virtual controls or joystick lever center- called the zero point, at which the speed is zero.
The speed of pan and tilt movements is determined by the location of the mouse pointer on the virtual joystick or the joystick handle relative to the center point; the speed of the zoom in and out movement is determined by the location of the mouse pointer relative to the center point of the zoom lever or the zoom control head on a joystick handle. The further away from the zero point, the quicker the camera will move. The closer to the zero point, the slower the camera will move.