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java.lang.Object org.geotools.graph.traverse.basic.AbstractGraphIterator org.geotools.graph.traverse.basic.SourceGraphIterator org.geotools.graph.traverse.standard.DijkstraIterator
Iterates over the nodes of a graph in pattern using Dijkstra's
Shortest Path Algorithm. A Dijkstra iteration returns nodes
in an order of increasing cost relative to a specified node
(the source node of the iteration).
In a Dijsktra iteration, a weight is associated with each edge
and a cost with each node. The iteration operates by maintaining
two sets of nodes. The first the set of nodes whose final cost is known, and
the second is the set of nodes whose final cost is unknown.
Initially, every node except for the source node has a cost of infinity, and
resides in the unkown set. The source node has a cost of zero, and is
is a member of the known set.
The iteration operatates as follows:
sn = source node of iteration N = set of all nodes K = set of nodes with known cost = {sn} U = set of nodes with unknown cost = N - K cost(sn) = 0 for each node $un in U cost(un) = infinity while(|U| > 0) for each node n in K find a node un in U that relates to n if cost(n) + weight(n,un) < cost(un) cost(un) = cost(n) + weight(n,un) ln = node with least cost in U remove ln from U add ln to K return ln as next node in iterationThe following is an illustration of the algorithm. Edge weights are labelled in blue and the final node costs are labelled in red.
Nested Class Summary | |
protected static class |
DijkstraIterator.DijkstraNode
Internal data structure used to track node costs, and parent nodes. |
static interface |
DijkstraIterator.EdgeWeighter
Supplies a weight for each edge in the graph to be used by the iteration when calculating node costs. |
Constructor Summary | |
DijkstraIterator(DijkstraIterator.EdgeWeighter weighter)
Constructs a new Dijkstra iterator which uses the specided EdgeWeighter. |
Method Summary | |
void |
cont(Graphable current,
GraphTraversal traversal)
Looks for adjacent nodes to the current node which are in the adjacent node and updates costs. |
double |
getCost(Graphable component)
Returns the internal cost of a node which has been calculated by the iterator. |
Graphable |
getParent(Graphable component)
Returns the last node in the known set to update the node. |
protected PriorityQueue |
getQueue()
|
protected java.util.Iterator |
getRelated(Graphable current)
|
void |
init(Graph graph,
GraphTraversal traversal)
Builds internal priority queue to manage node costs. |
void |
killBranch(Graphable current,
GraphTraversal traversal)
Kills the branch of the traversal by not updating the cost of any adjacent nodes. |
Graphable |
next(GraphTraversal traversal)
Returns the next node in the priority queue. |
Methods inherited from class org.geotools.graph.traverse.basic.SourceGraphIterator |
getSource, setSource |
Methods inherited from class org.geotools.graph.traverse.basic.AbstractGraphIterator |
getGraph, getTraversal, getWalker, setTraversal |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
public DijkstraIterator(DijkstraIterator.EdgeWeighter weighter)
weighter
- Calculates weights for edges in the graph being iterated
over.Method Detail |
public void init(Graph graph, GraphTraversal traversal)
graph
- The graph being whose components are being iterated over.org.geotools.graph.traverse.GraphIterator#init(Graph)
public Graphable next(GraphTraversal traversal)
org.geotools.graph.traverse.GraphIterator#next()
public void cont(Graphable current, GraphTraversal traversal)
current
- The current component of the traversal.org.geotools.graph.traverse.GraphIterator#cont(Graphable)
public void killBranch(Graphable current, GraphTraversal traversal)
current
- The current component of the traversal.org.geotools.graph.traverse.GraphIterator#killBranch(Graphable)
public double getCost(Graphable component)
component
- The component whose cost to return.
public Graphable getParent(Graphable component)
component
- The node whose parent to return (child)
protected PriorityQueue getQueue()
protected java.util.Iterator getRelated(Graphable current)
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