The vrpend example illustrates the various ways a dynamic model in Simulink® can interact with a virtual reality world. It is the model of 2-dimensional inverted pendulum controlled by a PID controller. What distinguishes this model from 'common' inverted pendulum models is visualization and the methods of setting the setpoint. You visualize and interact with a virtual world by using a Trajectory Graph and VR Sink blocks. The Trajectory Graph block allows you to track the history of the pendulum position and change the setpoint. The method for setting the setpoint can be selected in the mask of the Trajectory Graph block. The following methods are available:
- Mouse - Click-and-drag a mouse pointer in the Trajectory Graph 2-D window
- Input Signal - External Trajectory Graph input in this model driven by a random number generator
- VR Sensor - Activates the input from a VRML TouchSensor
When the pointing device in the VRML viewer moves over an active TouchSensor area, the cursor shape changes from an arrow to a hand shape. When the setpoint selection method is set to VRSensor, left mouse button click sets the new setpoint value.
Notice the pseudo orthographic view defined in the associated VRML file. This effect is achieved by creating a viewpoint which is located far from the object of interest with a very narrow view defined by the VRML FieldOfView parameter. An orthographic view is useful for eliminating the panoramic distortion that occurs when using a wide-angle lens. This technique is also known in photography. The fallback of this technique is that locating the viewpoint in a distance makes the standard viewer navigation tricky or difficult in some navigation modes. If you want to navigate around the virtual pendulum bench, we recommend that you switch to some other viewpoint.