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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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