A turn refers to the process of moving from one edge through an intermediate node to an adjacent edge. Turn cost represents the expense required to complete the turn. The turn table is used to store turn cost values. It must list all possible turns at each intersection, typically containing four fields: start edge field (FromEdgeID), end edge field (ToEdgeID), node ID field (NodeID), and turn cost field (TurnCost). These fields correlate with those in edges and nodes. Each record in the table represents the edge cost required for a specific way of passing through an intersection. Turn costs are typically directional, with a value of -1 indicating prohibited turns.
This section will introduce you to the following:
Caution: The unit of cost depends on its actual content. If the cost field represents time expenditure, the unit would be time-based (e.g., hours, minutes, seconds). If it represents distance expenditure, the unit would be distance-based (e.g., meters, kilometers, feet).