org.opentripplanner.astar.spi.AStarEdge Maven / Gradle / Ivy
package org.opentripplanner.astar.spi;
/**
* Represents an edge in the street network. Most edges have a one-to-one mapping to real world
* things like street segments or stairs.
* However, there can be other edges that represent concepts that are invisible and only present
* in OTP's model. These are things that link entities like transit stops and rental vehicles to the
* street network. The links are necessary in order for A* to discover them and can contain logic for
* access permissions. For example, a car can not use an edge that links the
* street network with a transit stop to prevent a straight transfer from car to transit.
*/
public interface AStarEdge<
State extends AStarState,
Edge extends AStarEdge,
Vertex extends AStarVertex
> {
Vertex getFromVertex();
Vertex getToVertex();
/**
* Traverse the edge from a given state and return the result of the traversal.
*
* @param s0 The 'current' state when arriving at the fromVertex.
* @return The array of states that are the result of the state (the passenger) moving (traversing)
* through the edge.
*
* In most cases this is a single state where, for example, the weight (cost) and time are
* increased according to the properties of the edge.
*
* However, it is also possible that this edge is not traversable for the current state,
* for example if it's a walk-only edge but the state is arriving in a car. In such a
* case an empty array is returned (see {@link org.opentripplanner.street.search.state.State#empty()}).
* The Astar algorithm won't then explore this state any further as the destination is not
* reachable through this state/edge combination.
*
* Lastly, there can also be cases where more than one state is returned: For example
* when a state is renting a free-floating vehicle but the edge is in a no-drop-off zone.
* In such a case two resulting states are possible: one where the state continues on the
* rental vehicle (as you may exit the no-drop-off zone later) and a second state where the
* vehicle is speculatively dropped off and the passenger continues on foot in case
* that the destination is inside the zone.
*/
State[] traverse(State s0);
}