The process by which LEGION Simulator calculates and assigns the movements of Entities is called 'auto-navigation'. This does not require manual intervention by modellers once a model is ready to simulate (in rare instances, you may wish to override Auto-navigation; see Setting Model Properties ). As long as a model is free of errors and all Entities have been assigned targets or Final Destinations, Auto-navigation will take care of their movement through the model.

In calculating Entity movements, LEGION Simulator uses the concept of 'minimum cost’ (which can also be expressed as ‘maximum utility’) as the cornerstone of pedestrian logic. Entities attempt to minimise their personal dissatisfaction when choosing their next step. Dissatisfaction is caused by physical and psychological factors that degrade the quality of their journey. The following three factors contribute to an Entity's overall experience of 'dissatisfaction':

• Frustration – having to slow down in congested spaces.
• Inconvenience – the degree to which an Entity must divert from its preferred shortest distance.
• Discomfort – the perceived lack of adequate personal space.

Navigation decisions are made at three levels:

• Strategic – choice of target
• Tactical – route selection and macro-navigation
• Local – micro-navigation

Choice of target is the process of translating an Entity's objectives (such as ’to leave the venue’, ’to buy a ticket’) into targets (such as ’exit’, ’ticket machine’). In many cases, there are multiple ways in which an objective can be achieved and you express this relationship by specifying a Final Destination for an Entity and by adding links to connect Spatial Objects together as part of an itinerary. This enables Entities to 'understand' which alternatives are available to them.

To specify how Entities choose between alternative intermediary targets, you can enable one of four methods of linking. Whichever linking method you opt for, it is important to remember that the assignment of a target at this stage is a starting point and does not always dictate an Entity's final choice. Even Final Destinations can be changed en route (by Direction Modifiers).

The four linking methods you can select for Spatial Objects are:

• Link by Percentage Weighting
• Link by Entity Type
• Link by Entity Choice
• Link by Final Destination

Macro-navigation is the process whereby an Entity finds the shortest route from its current position to its next target. This shortest route takes into account the geometry of the site and the length of several paths are considered and compared.

An individual trajectory is the result of micro-navigation. LEGION Entities have a 'perception zone' which is adjusted dynamically and is based on instantaneous information and accumulated memories.

Within this perception zone Entities assess information in order to decide their next best-step. Their decision is influenced by: the type of area they find themselves in (the context); the Entities and obstacles near them; their walking preferences, which are part of their profile (their Entity Type); and their general desire to get to their target in the least dissatisfying way.

Additionally, some Entities designated as ‘congestion avoiders’ may, in the course of deciding their next step, decide to change target altogether.

As with any model, the quality of the inputs and assumptions influences the quality of the results. Where possible we encourage observation and the measurement of comparable circumstances to 'sense-check' the quality of model assumptions.