A person’s evacuation consists of sequential movements from one boundary to another. Upon reaching a boundary, the person selects the next boundary to move toward. The evacuation is considered complete when the person reaches the boundary corresponding to their assigned exit.
The selection of the next boundary depends on:
- the evacuation modeling settings,
- the person’s assigned exit,
- the distance from the person’s current position to each available boundary.
The distance to a boundary is determined using the path graph associated with that boundary.
Path Planning Before Movement Begins
Path planning for each individual consists of several steps:
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Determine the area in which the person is currently located.
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Determine the exit to which the person will evacuate:
- If a specific exit is assigned to the person, the system checks whether that exit is available. If the assigned exit is unavailable, the nearest available exit is selected instead.
- If no specific exit is assigned, the nearest available exit is chosen automatically.
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Determine the first boundary the person should move toward. If multiple such boundaries exist (e.g., the person is approximately equidistant from two stairwells leading to the exit), the selection is made probabilistically, based on the relative distances to the available options.
Selecting the Next Boundary
Once a person reaches an intermediate boundary, they must choose the next boundary toward which to move.
The selection depends on the value of the evacuation modeling parameter Path Selection Algorithm:
If the Shortest Path method is selected, the person will choose the nearest boundary within the current area that brings them closer to the exit.
If the Alternative Paths method is selected, the boundary will be chosen probabilistically according to the distribution shown in the corresponding diagram.
Changing the Boundary During Movement
If multiple boundaries leading to the exit are available to a person, they may change their current target boundary while en route.
A boundary change occurs when the following conditions are met:
- The Alternative Paths path selection algorithm is enabled in the evacuation modeling settings.
- The person has line of sight to both the current and the new boundary (i.e., no obstacles exist between them on the navigation graph).
- The current and new boundaries are located at approximately the same distance from the exit.
- The number of people moving toward the current boundary is greater than the number of people heading to the new boundary.