What is Simulation “Fidelity?”

Posted by Todd Borghesani

While the use of the term “fidelity” is familiar to most involved in simulation, it is term that has been used loosely and without absolute understanding. ‘Fidelity’ as a word has been generalized and used by the simulation community with such cloaked meaning to a point where the term “high fidelity“ has gained ephemeral characteristics.

So what does fidelity really mean?

Within the simulation community there is a widespread understanding that fidelity describes the extent to which a simulation replicates the system it represents.

fidelity. 1. The degree to which a model or simulation reproduces the state and behavior of a real world object or the perception of a real world object, feature, condition, or chosen standard in a measurable or perceivable manner; a measure of the realism of a model or simulation; faithfulness. Fidelity should generally be described with respect to the measures, standards or perceptions used in assessing or stating it. See accuracy, sensitivity, precision, resolution, repeatability, model/simulation validation.

2. The methods, metrics, and descriptions of models or simulations used to compare those models or simulations to their real world referents or to other simulations in such terms as accuracy, scope, resolution, level of detail, level of abstraction and repeatability. Fidelity can characterize the representations of a model, a simulation, the data used by a simulation (e.g., input, characteristic or parametric), or an exercise. Each of these fidelity types has different implications for the applications that employ these representations.

Reality is not Realistic

A common and frequent contributor to fidelity disputes is the unrelenting desire of end-users and less experienced flight simulator buyers to pursue reality as a fidelity standard. Affordable simulation technology cannot deliver reality. Reality is only approachable with through disproportionate financial and technology investment. Marketing hyperbole such as “virtual reality“ and ‘zero flight time flight simulators’, and carefully crafted demonstrations that avoid revealing fidelity limitations have carelessly fueled this erroneous marketplace expectation.

Simulation reality is a paradox as such fidelity performance is not an economic reality. Fidelity is being driven by the glamour and appeal of technology, where reality as a fidelity measure is being pursued with increasing gusto and vigor. Fidelity is being pursued in the same way in which car enthusiasts view up-market models and sports cars. The badge affixed to the hood and what is under the hood seems more important than the basic purpose for owning the car – transportation. It is time for fidelity to be brought back to the reality of being measured in the context of its intended purpose, and not in the context of congruence with the real world.

There is growing evidence that suggests reality is not the optimum fidelity solution for training purposes. Beyond reality techniques, using non-real world effects to demonstrate teaching points is emerging as an effective training technique. There is also research into variable time execution as a training technique, where simulations run at slower than real-time, and faster than real-time have demonstrated more effective training outcomes than the same training conducted in real-time. Reality is not an immutable fidelity objective.

Focus on Intended Purpose and Value

A fundamental condition to bring fidelity back from the realm of reality is a sound understanding of the intended purpose for which the simulator is to be used (i.e. the capability required), the fidelity necessary to achieve the required capability, and the cost nexus between fidelity and capability. The latter parameter is important to determine the economic break point at which increasing fidelity or capability represents diminishing value or return on investment.

Fidelity is of no use to a simulator if it does not directly contribute to the capability or end use served by the flight simulator. The paradigm for defining fidelity should therefore be capability-stimuli-fidelity. Decide on what capability (end use) is required, assess the stimuli required to deliver that capability, and then derive the fidelity needed to effectively apply the stimuli. Establishing the relationship between fidelity and capability will also allow economic rationalization of proposed fidelity levels, thereby bring value into the equation. Increasing levels of fidelity come at an increasing price.

It is important to be able to define and rationalize fidelity capability relationships to identify value break points. Excess fidelity has an excessive price that must be avoided if value is to be achieved.

Author Biography

Simulation Fidelity — Getting in Touch with Reality, was written by Geoff Northam. Geoff has been involved in flight simulator procurement for the Royal Australian Air Force for over thirteen years, fulfilling engineering and project management roles. His experiences include project management of the RAAF F/A-18 Operational Flight Trainers, F-111C Mission Simulator, and AP-3C Advanced Flight Simulator. Geoff left the Royal Australian Air Force after 22 years service and is now employed by Computer Sciences Corporation, where he is currently performing project management duties for the RAN SH-2G(A) Full Mission Flight Simulator. Geoff Northam is a graduate of the Royal Australian Air Force Academy and the Royal Australian Navy Staff College.Geoff is also the current Chairman of the Simulation Industry Association of Australia.

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