Table of Contents
This is a simple guide to walk you through the steps of getting started with pgRouting. In this guide we will cover:
The first thing we need to do is create a database and load pgrouting in the database. Typically you will create a database for each project. Once you have a database to work in, your can load your data and build your application in that database. This makes it easy to move your project later if you want to to say a production server.
For Postgresql 9.2 and later versions
createdb mydatabase
psql mydatabase c "create extension postgis"
psql mydatabase c "create extension pgrouting"
How you load your data will depend in what form it comes it. There are various OpenSource tools that can help you, like:
osm2pgrouting: 


shp2pgsql: 

ogr2ogr: 

osm2pgsql: 

So these tools and probably others will allow you to read vector data so that you may then load that data into your database as a table of some kind. At this point you need to know a little about your data structure and content. One easy way to browse your new data table is with pgAdmin3 or phpPgAdmin.
Next we need to build a topology for our street data. What this means is that for any given edge in your street data the ends of that edge will be connected to a unique node and to other edges that are also connected to that same unique node. Once all the edges are connected to nodes we have a graph that can be used for routing with pgrouting. We provide a tool that will help with this:
Note
this step is not needed if data is loaded with osm2pgrouting
select pgr_createTopology('myroads', 0.000001);
There are lots of possible sources for errors in a graph. The data that you started with may not have been designed with routing in mind. A graph has some very specific requirements. One is that it is NODED, this means that except for some very specific use cases, each road segment starts and ends at a node and that in general is does not cross another road segment that it should be connected to.
There can be other errors like the direction of a oneway street being entered in the wrong direction. We do not have tools to search for all possible errors but we have some basic tools that might help.
select pgr_analyzegraph('myroads', 0.000001);
select pgr_analyzeoneway('myroads', s_in_rules, s_out_rules,
t_in_rules, t_out_rules
direction)
select pgr_nodeNetwork('myroads', 0.001);
Once you have all the preparation work done above, computing a route is fairly easy. We have a lot of different algorithms that can work with your prepared road network. The general form of a route query is:
select pgr_dijkstra(`SELECT * FROM myroads', 1, 2)
As you can see this is fairly straight forward and you can look and the specific algorithms for the details of the signatures and how to use them. These results have information like edge id and/or the node id along with the cost or geometry for the step in the path from start to end. Using the ids you can join these result back to your edge table to get more information about each step in the path.
There are several kinds of valid inner queries and also the columns returned are depending of the function.. Which kind of edges_sql will depend on the function(s) requirements.
edges_sql:  an SQL query, which should return a set of rows with the following columns: 

Column  Type  Default  Description 

id  ANYINTEGER  Identifier of the edge.  
source  ANYINTEGER  Identifier of the first end point vertex of the edge.  
target  ANYINTEGER  Identifier of the second end point vertex of the edge.  
cost  ANYNUMERICAL  Weight of the edge (source, target)


reverse_cost  ANYNUMERICAL  1  Weight of the edge (target, source),

Where:
ANYINTEGER:  SMALLINT, INTEGER, BIGINT 

ANYNUMERICAL:  SMALLINT, INTEGER, BIGINT, REAL, FLOAT 
edges_sql:  an SQL query, which should return a set of rows with the following columns: 

Column  Type  Default  Description 

source  ANYINTEGER  Identifier of the first end point vertex of the edge.  
target  ANYINTEGER  Identifier of the second end point vertex of the edge.  
cost  ANYNUMERICAL  Weight of the edge (source, target)


reverse_cost  ANYNUMERICAL  1  Weight of the edge (target, source),

Where:
ANYINTEGER:  SMALLINT, INTEGER, BIGINT 

ANYNUMERICAL:  SMALLINT, INTEGER, BIGINT, REAL, FLOAT 
edges_sql:  an SQL query, which should return a set of rows with the following columns: 

Column  Type  Default  Description 

id  ANYINTEGER  Identifier of the edge.  
source  ANYINTEGER  Identifier of the first end point vertex of the edge.  
target  ANYINTEGER  Identifier of the second end point vertex of the edge.  
cost  ANYNUMERICAL  Weight of the edge (source, target)


reverse_cost  ANYNUMERICAL  1  Weight of the edge (target, source),

x1  ANYNUMERICAL  X coordinate of source vertex.  
y1  ANYNUMERICAL  Y coordinate of source vertex.  
x2  ANYNUMERICAL  X coordinate of target vertex.  
y2  ANYNUMERICAL  Y coordinate of target vertex. 
Where:
ANYINTEGER:  SMALLINT, INTEGER, BIGINT 

ANYNUMERICAL:  SMALLINT, INTEGER, BIGINT, REAL, FLOAT 
edges_sql:  an SQL query, which should return a set of rows with the following columns: 

Column  Type  Default  Description 

id  ANYINTEGER  Identifier of the edge.  
source  ANYINTEGER  Identifier of the first end point vertex of the edge.  
target  ANYINTEGER  Identifier of the second end point vertex of the edge.  
capacity  ANYINTEGER  Weight of the edge (source, target)


reverse_capacity  ANYINTEGER  1  Weight of the edge (target, source),

Where:
ANYINTEGER:  SMALLINT, INTEGER, BIGINT 

points_sql:  an SQL query, which should return a set of rows with the following columns: 

Column  Type  Description 

pid  ANYINTEGER  (optional) Identifier of the point.

edge_id  ANYINTEGER  Identifier of the “closest” edge to the point. 
fraction  ANYNUMERICAL  Value in <0,1> that indicates the relative postition from the first end point of the edge. 
side  CHAR  (optional) Value in [‘b’, ‘r’, ‘l’, NULL] indicating if the point is:

Where:
ANYINTEGER:  smallint, int, bigint 

ANYNUMERICAL:  smallint, int, bigint, real, float 
There are several kinds of columns returned are depending of the function.
Returns set of (seq, path_seq [, start_vid] [, end_vid], node, edge, cost, agg_cost)
Column  Type  Description 

seq  INT  Sequential value starting from 1. 
path_id  INT  Path identifier. Has value 1 for the first of a path. Used when there are multiple paths for the same start_vid to end_vid combination. 
path_seq  INT  Relative position in the path. Has value 1 for the beginning of a path. 
start_vid  BIGINT  Identifier of the starting vertex. Used when multiple starting vetrices are in the query. 
end_vid  BIGINT  Identifier of the ending vertex. Used when multiple ending vertices are in the query. 
node  BIGINT  Identifier of the node in the path from start_vid to end_vid. 
edge  BIGINT  Identifier of the edge used to go from node to the next node in the path sequence. 1 for the last node of the path. 
cost  FLOAT  Cost to traverse from node using edge to the next node in the path sequence. 
agg_cost  FLOAT  Aggregate cost from start_v to node. 
Returns set of (start_vid, end_vid, agg_cost)
Column  Type  Description 

start_vid  BIGINT  Identifier of the starting vertex. Used when multiple starting vetrices are in the query. 
end_vid  BIGINT  Identifier of the ending vertex. Used when multiple ending vertices are in the query. 
agg_cost  FLOAT  Aggregate cost from start_vid to end_vid. 
Column  Type  Description 

seq  INT  Sequential value starting from 1. 
edge_id  BIGINT  Identifier of the edge in the original query(edges_sql). 
source  BIGINT  Identifier of the first end point vertex of the edge. 
target  BIGINT  Identifier of the second end point vertex of the edge. 
flow  BIGINT  Flow through the edge in the direction (source, target). 
residual_capacity  BIGINT  Residual capacity of the edge in the direction (source, target). 
Overview
Typically when GIS files are loaded into the data database for use with pgRouting they do not have topology information associated with them. To create a useful topology the data needs to be “noded”. This means that where two or more roads form an intersection there it needs to be a node at the intersection and all the road segments need to be broken at the intersection, assuming that you can navigate from any of these segments to any other segment via that intersection.
You can use the graph analysis functions to help you see where you might have topology problems in your data. If you need to node your data, we also have a function pgr_nodeNetwork() that might work for you. This function splits ALL crossing segments and nodes them. There are some cases where this might NOT be the right thing to do.
For example, when you have an overpass and underpass intersection, you do not want these noded, but pgr_nodeNetwork does not know that is the case and will node them which is not good because then the router will be able to turn off the overpass onto the underpass like it was a flat 2D intersection. To deal with this problem some data sets use zlevels at these types of intersections and other data might not node these intersection which would be ok.
For those cases where topology needs to be added the following functions may be useful. One way to prep the data for pgRouting is to add the following columns to your table and then populate them as appropriate. This example makes a lot of assumption like that you original data tables already has certain columns in it like one_way, fcc, and possibly others and that they contain specific data values. This is only to give you an idea of what you can do with your data.
ALTER TABLE edge_table
ADD COLUMN source integer,
ADD COLUMN target integer,
ADD COLUMN cost_len double precision,
ADD COLUMN cost_time double precision,
ADD COLUMN rcost_len double precision,
ADD COLUMN rcost_time double precision,
ADD COLUMN x1 double precision,
ADD COLUMN y1 double precision,
ADD COLUMN x2 double precision,
ADD COLUMN y2 double precision,
ADD COLUMN to_cost double precision,
ADD COLUMN rule text,
ADD COLUMN isolated integer;
SELECT pgr_createTopology('edge_table', 0.000001, 'the_geom', 'id');
The function pgr_createTopology() will create the vertices_tmp table and populate the source and target columns. The following example populated the remaining columns. In this example, the fcc column contains feature class code and the CASE statements converts it to an average speed.
UPDATE edge_table SET x1 = st_x(st_startpoint(the_geom)),
y1 = st_y(st_startpoint(the_geom)),
x2 = st_x(st_endpoint(the_geom)),
y2 = st_y(st_endpoint(the_geom)),
cost_len = st_length_spheroid(the_geom, 'SPHEROID["WGS84",6378137,298.25728]'),
rcost_len = st_length_spheroid(the_geom, 'SPHEROID["WGS84",6378137,298.25728]'),
len_km = st_length_spheroid(the_geom, 'SPHEROID["WGS84",6378137,298.25728]')/1000.0,
len_miles = st_length_spheroid(the_geom, 'SPHEROID["WGS84",6378137,298.25728]')
/ 1000.0 * 0.6213712,
speed_mph = CASE WHEN fcc='A10' THEN 65
WHEN fcc='A15' THEN 65
WHEN fcc='A20' THEN 55
WHEN fcc='A25' THEN 55
WHEN fcc='A30' THEN 45
WHEN fcc='A35' THEN 45
WHEN fcc='A40' THEN 35
WHEN fcc='A45' THEN 35
WHEN fcc='A50' THEN 25
WHEN fcc='A60' THEN 25
WHEN fcc='A61' THEN 25
WHEN fcc='A62' THEN 25
WHEN fcc='A64' THEN 25
WHEN fcc='A70' THEN 15
WHEN fcc='A69' THEN 10
ELSE null END,
speed_kmh = CASE WHEN fcc='A10' THEN 104
WHEN fcc='A15' THEN 104
WHEN fcc='A20' THEN 88
WHEN fcc='A25' THEN 88
WHEN fcc='A30' THEN 72
WHEN fcc='A35' THEN 72
WHEN fcc='A40' THEN 56
WHEN fcc='A45' THEN 56
WHEN fcc='A50' THEN 40
WHEN fcc='A60' THEN 50
WHEN fcc='A61' THEN 40
WHEN fcc='A62' THEN 40
WHEN fcc='A64' THEN 40
WHEN fcc='A70' THEN 25
WHEN fcc='A69' THEN 15
ELSE null END;
 UPDATE the cost information based on oneway streets
UPDATE edge_table SET
cost_time = CASE
WHEN one_way='TF' THEN 10000.0
ELSE cost_len/1000.0/speed_kmh::numeric*3600.0
END,
rcost_time = CASE
WHEN one_way='FT' THEN 10000.0
ELSE cost_len/1000.0/speed_kmh::numeric*3600.0
END;
 clean up the database because we have updated a lot of records
VACUUM ANALYZE VERBOSE edge_table;
Now your database should be ready to use any (most?) of the pgRouting algorithms.
Overview
It is common to find problems with graphs that have not been constructed fully noded or in graphs with zlevels at intersection that have been entered incorrectly. An other problem is one way streets that have been entered in the wrong direction. We can not detect errors with respect to “ground” truth, but we can look for inconsistencies and some anomalies in a graph and report them for additional inspections.
We do not current have any visualization tools for these problems, but I have used mapserver to render the graph and highlight potential problem areas. Someone familiar with graphviz might contribute tools for generating images with that.
With pgr_analyzeGraph the graph can be checked for errors. For example for table “mytab” that has “mytab_vertices_pgr” as the vertices table:
SELECT pgr_analyzeGraph('mytab', 0.000002);
NOTICE: Performing checks, pelase wait...
NOTICE: Analyzing for dead ends. Please wait...
NOTICE: Analyzing for gaps. Please wait...
NOTICE: Analyzing for isolated edges. Please wait...
NOTICE: Analyzing for ring geometries. Please wait...
NOTICE: Analyzing for intersections. Please wait...
NOTICE: ANALYSIS RESULTS FOR SELECTED EDGES:
NOTICE: Isolated segments: 158
NOTICE: Dead ends: 20028
NOTICE: Potential gaps found near dead ends: 527
NOTICE: Intersections detected: 2560
NOTICE: Ring geometries: 0
pgr_analyzeGraph

OK
(1 row)
In the vertices table “mytab_vertices_pgr”:
 Deadends are identified by cnt=1
 Potencial gap problems are identified with chk=1.
SELECT count(*) as deadends FROM mytab_vertices_pgr WHERE cnt = 1;
deadends

20028
(1 row)
SELECT count(*) as gaps FROM mytab_vertices_pgr WHERE chk = 1;
gaps

527
(1 row)
For isolated road segments, for example, a segment where both ends are deadends. you can find these with the following query:
SELECT *
FROM mytab a, mytab_vertices_pgr b, mytab_vertices_pgr c
WHERE a.source=b.id AND b.cnt=1 AND a.target=c.id AND c.cnt=1;
If you want to visualize these on a graphic image, then you can use something like mapserver to render the edges and the vertices and style based on cnt or if they are isolated, etc. You can also do this with a tool like graphviz, or geoserver or other similar tools.
pgr_analyzeOneway analyzes one way streets in a graph and identifies any flipped segments. Basically if you count the edges coming into a node and the edges exiting a node the number has to be greater than one.
This query will add two columns to the vertices_tmp table ein int and eout int and populate it with the appropriate counts. After running this on a graph you can identify nodes with potential problems with the following query.
The rules are defined as an array of text strings that if match the col value would be counted as true for the source or target in or out condition.
Lets assume we have a table “st” of edges and a column “one_way” that might have values like:
 ‘FT’  oneway from the source to the target node.
 ‘TF’  oneway from the target to the source node.
 ‘B’  two way street.
 ‘’  empty field, assume twoway.
 <NULL>  NULL field, use two_way_if_null flag.
Then we could form the following query to analyze the oneway streets for errors.
SELECT pgr_analyzeOneway('mytab',
ARRAY['', 'B', 'TF'],
ARRAY['', 'B', 'FT'],
ARRAY['', 'B', 'FT'],
ARRAY['', 'B', 'TF'],
);
 now we can see the problem nodes
SELECT * FROM mytab_vertices_pgr WHERE ein=0 OR eout=0;
 and the problem edges connected to those nodes
SELECT gid FROM mytab a, mytab_vertices_pgr b WHERE a.source=b.id AND ein=0 OR eout=0
UNION
SELECT gid FROM mytab a, mytab_vertices_pgr b WHERE a.target=b.id AND ein=0 OR eout=0;
Typically these problems are generated by a break in the network, the one way direction set wrong, maybe an error related to zlevels or a network that is not properly noded.
The above tools do not detect all network issues, but they will identify some common problems. There are other problems that are hard to detect because they are more global in nature like multiple disconnected networks. Think of an island with a road network that is not connected to the mainland network because the bridge or ferry routes are missing.
To get faster results bound your queries to the area of interest of routing to have, for example, no more than one million rows.
Use an inner query SQL that does not include some edges in the routing function
SELECT id, source, target from edge_table WHERE
id < 17 and
the_geom && (select st_buffer(the_geom,1) as myarea FROM edge_table where id = 5)
Integrating the inner query to the pgRouting function:
SELECT * FROM pgr_dijkstra(
'SELECT id, source, target from edge_table WHERE
id < 17 and
the_geom && (select st_buffer(the_geom,1) as myarea FROM edge_table where id = 5)',
1, 2)
When “you know” that you are going to remove a set of edges from the edges table, and without those edges you are going to use a routing function you can do the following:
Analize the new topology based on the actual topology:
pgr_analyzegraph('edge_table',rows_where:='id < 17');
Or create a new topology if the change is permanent:
pgr_createTopology('edge_table',rows_where:='id < 17');
pgr_analyzegraph('edge_table',rows_where:='id < 17');
Wiki
Adding Functionaity to pgRouting
Consult the developer’s documentation
Indices and tables