1. FOSS4G2007
Presentation
Shortest path search in real
road networks with
pgRouting
pgRouting Anton Patrushev (Orkney, Inc.)
Shortest path search in real road networks
with pgRouting 1

2. Introduction
pgRouting is an extension of PostgreSQL and PostGIS.
A predecessor of pgRouting ­ pgDijkstra, written by Sylvain Pasche
from Camptocamp, was extended by Orkney (Japan) and renamed
to pgRouting.
pgRouting includes:
* Shortest path search (Dijkstra, A*, Shooting*)
* Traveling Salesperson Problem (TSP) solution
* Driving distance polygon calculation
Shortest path search in real road networks
with pgRouting 2

3. How it works
Pl/PgSQL SQL query
C++ core C wrapper
function (data)
Shortest path search in real road networks
with pgRouting 3

4. Shortest path algorithms
●
Dijkstra
●
Well known and fair shortest path algorithm
●
Always finds mathematically shortest path
●
Good for sparse networks
●
A*
●
Well known heuristic shortest path algorithm
●
Needs vertex geometry information
●
Searches through less number of vertexes
●
Good for dense networks
●
Shooting*
Shortest path search in real road networks
with pgRouting 4

5. Shooting*
●
Edge­based heuristic shortest path algorithm
●
Supports maneuver restrictions and traffic lights
●
Properly processes parallel edges
●
Good for dense networks
Predecessors:
●
Modified A* ­ Wolfgang Schmid, 2000, Stephan Winter, 2002
●
C* ­ Ingrid Flinsenberg, 2004
Shortest path search in real road networks
with pgRouting 5

6. Comparison with other
algorithms
Dijkstra cost=cost(vertex1, vertex2)
Each vertex can be visited only once
A* cost=cost(vertex1, vertex2)+H(vertex1, vertex2)
Each vertex can be visited only once
Shooting* cost=cost(edge1)+cost(edge1, edge2)+H(edge1)
Each edge can be visited only once
Parallel edges handling
Dijkstra/A* Shooting*
Shortest path search in real road networks
with pgRouting 6

7. Real road networks
A B C
A)Signs (restrict maneuvers)
B)Traffic lights (delays)
C)Road marking (restrict maneuvers)
Shortest path search in real road networks
with pgRouting 7

8. Network representation
d d c
f
d
a b c a b c
cost(eb,ab)=1min a b
cost(eb,bd)=1min
cost(eb,bc)=∞ cost(eb,bc)=1min cost(ab,bd,df)=∞
e e ... e
B ...
A C
...
A)Right turn costs too much
B)Driving through vertex b passage costs extra
C)Driving from a to f costs too much
Shortest path search in real road networks
with pgRouting 8

9. Routing data structure
Dijkstra
A*
Shooting*
Edge Edge Edge
●
id
●
id ●
id
●
cost
●
cost ●
cost
●
reverse_cost
●
reverse_cost ●
reverse_cost
●
Source vertex
●
Source vertex ●
Adjacent edge
●
id
●
id ●
rule
●
Target vertex
●
x ●
to_cost
●
id
●
y ●
Source vertex
●
Target vertex ●
id
●
id ●
x
●
x ●
y
●
y ●
Target vertex
●
id
●
x
●
y
Shortest path search in real road networks
with pgRouting 9

10. Thank you!
pgrouting.postlbs.org
orkney.co.jp
pgRouting
Shortest path search in real road networks
with pgRouting 10