Requirements on Simulators

Requirements on Simulators

The real-time requirements on a simulator vary depending on the nature of these four components. Two key performance requirements on a simulator are frame rate and transport delay.

Frame Rate

A crucial measure of simulator performance is the rate at which it updates the display. This rate is called the frame rate, whether or not the simulator displays its model on a video screen.

Frame rate is given in cycles per second (abbreviated Hz). Typical frame rates run from 15 Hz to 60 Hz, although rates higher and lower than these are used in special situations.

The inverse of frame rate is frame interval. For example, a frame rate of 60 Hz implies a frame interval of 1/60 second, or 16.67 milliseconds. To maintain a frame rate of 60 Hz, a simulator must update its model and prepare a new display in less than 16.67 ms.

The REACT/Pro Frame Scheduler helps you organize a multi-process application to achieve a specified frame rate. (See Chapter 7, "Using the Frame Scheduler.")

Transport Delay

Transport delay is the term for the number of frames that elapses before a control motion is reflected in the display. When the transport delay is too long, the operator will perceive the simulation as sluggish or unrealistic. If a visual display lags behind control inputs, a human operator can become physically ill.