How to: v1.x

pgRouting v1.x

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• This page is Historical

Here you can find the "How to" for that version.

Creating Data for Routing Applications

• Author: Daniel Kastl
• License: Creative Commons

Routing Engines always require the source and target nodes for every line in order to create a search for the shortest path. Creating this data on line networks involves creating a topology on that network.

Graphs, Directed, unDirected, Reverse Costs

The follow will hopefully explain a little bit about graphs and and how to use the directed and reverse cost arguments in the pgRouting function calls. If you use assign_vertex_id() to build your graph, it builds an undirected graph. Now you might have some oneway streets and you can create a reverse_cost column and start by populating it with the cost column values. Now you can treat you graph as a directed graph using the forward cost and reverse_cost for the cost to traverse an edge from A-B or B-A respectively. Since these values are all the same it is not very interesting, but if you have oneway streets you can now edit the cost or the reverse_cost values so that the wrong way has a very high cost. Many of the pgRouting function have boolean arguments '''directed''' and '''has_reverse_cost'''. If you set '''has_reverse_cost=true''', you should also set '''directed=true''' or it will ignore your reverse costs.

pgRouting

pgRouting gives the ability to create the source-target (start-end nodes) information within PostgreSQL using assign_vertex_id():

	SELECT assign_vertex_id(table_name, snapping_range, geometry_column_name, edge_id_column_name);

where table_name is the name of the edges table, nodes within snapping_range (value is in your current projection units) will be snapped, geometry_column_name is the name of the geometry column (usually 'the_geom'), edge_id_column_name is the name of the edge id column (usually gid).

This function requires 'source' and 'target' integer fields.

	ALTER TABLE ways ADD COLUMN source integer;
	ALTER TABLE ways ADD COLUMN target integer;
	SELECT assign_vertex_id('ways', 0.00001, 'the_geom', 'gid');

There is other software, that can be used to create a topology:

PostGIS

As of this writing, the latest PostGIS <http://www.postgis.net>_ 1.1.2, has started adding a topology functionality. But it is still in a very alpha stage and there are very little documentation yet on how to create the topology. This page will be updated once the topology functionality becomes stable enough to use.

ArcInfo

For those with an !ArcInfo license, creating a topology is done by just issuing the BUILD command:

	build line {Coverage Name}

and then exporting the coverage to a shape file, which can then be imported into PostGIS. The BUILD command will build fnode, tnode, length columns which can be renamed in PostgreSQL into source and target, and the length can be set as the intial cost.

GRASS

GRASS <http://grass.itc.it>_ can be used also to create a topology, but extracting the topology information and bringing it into PostgreSQL is not as simple as that of !ArcInfo's since the topolgy information is not included into with the data set when it is exported to a shape file.

The topolgy creation command "v.build" has a dump option though that will output the information into the stream which in turn can be piped into to a file. For example:

	v.build map=dourol option=build,dump > dourokukan.txt 

The output will be like this;

	---------- TOPOLOGY DUMP ----------
	N,S,E,W,T,B: 35.897887, 24.281578, 153.985841, 138.943042, 0.000000, 0.000000
	Nodes (148304 nodes, alive + dead ):
	node = 1, n_lines = 3, xy = 139.756532, 35.67451
	line = 1, type = 2, angle = -2.265356
	line = -20, type = 2, angle = -0.055499
	line = 8, type = 2, angle = 1.281166
	node = 2, n_lines = 3, xy = 139.756261, 35.674216
	line = -9, type = 2, angle = -2.827622
	line = 2, type = 2, angle = -1.878154
	...
	...
	...
	Lines (220672 lines, alive + dead ):
	line = 1, type = 2, offset = 14 n1 = 1, n2 = 2, left/area = 0, right = 0
	N,S,E,W,T,B: 35.674510, 35.674216, 139.756532, 139.756261, 0.000000, 0.000000
	line = 2, type = 2, offset = 79 n1 = 2, n2 = 3, left/area = 0, right = 0
	N,S,E,W,T,B: 35.674216, 35.672010, 139.756261, 139.755285, 0.000000, 0.000000
	line = 3, type = 2, offset = 160 n1 = 3, n2 = 4, left/area = 0, right = 0
	N,S,E,W,T,B: 35.672010, 35.671649, 139.755285, 139.755014, 0.000000, 0.000000

A perl program like :download:table_topo.pl <download/table_topo.pl> can be used to convert GRASS output into SQL files that will create node and line tables containing the topological information. These tables can then be linked into the PostGIS network table to create the source-target node information.

Network data validation

• Author: Kaib Behncke (edited by Daniel Kastl)
• License: Creative Commons

An important thing is to test if your data work properly for routing. If you are more or less fit to UMN MapServer you can easily do some tests. First of all many thank to Stephen WOODBRIDGE for that idea.

You need to type the following commands on your vertices_tmp-table

alter table vertices_tmp add column cnt integer;
update vertices_tmp set cnt=0;
update vertices_tmp set cnt=cnt+1 from ways where ways.source=vertices_tmp.id;
update vertices_tmp set cnt=cnt+1 from ways where ways.target=vertices_tmp.id;

This will display red dots at dead ends and green dots as good connections be segments.

You can visualize it with the UMN MapServer, just take a mapfile like:

	MAP 

	NAME           'mymap' 
	STATUS ON 
	#EXTENT 3427065.200000 5788323.530000 3443999.370000 5800691.660000
	#EXTENT 7.9189 52.2102 8.1716 52.3467
	EXTENT 880000 6840000 915000 6860000
	IMAGECOLOR 255 255 255
	SIZE      700 700
	SYMBOLSET    	'/your_path/symbols/symbols.sym'
	FONTSET       '/your_path/fonts/fonts.list'

	WEB
	TEMPLATE  'template.html'
	IMAGEPATH '/your_path/tmp/'
	IMAGEURL   '/tmp/'

	METADATA 
	'WMS_TITLE'   'Gastronomap_routing'
	 'WMS_FEATURE_INFO_MIME_TYPE' 'text/html'
	'WMS_ONLINERESOURCE'   'http://localhost/cgi-bin/mapserv?map=/your_path/routing.map' 		
		'WMS_SRS'       "EPSG:900913"	
	  END 
	END 

	PROJECTION 
	'init=epsg:900913'
	END 

	LAYER 
	OFFSITE 255 255 255
	#LABELITEM 'name'
	TOLERANCE 20
	NAME		'streets' 
	TYPE		LINE
	STATUS	DEFAULT
	CONNECTIONTYPE postgis
	CONNECTION 'user=postgres password=postgres dbname=routing host=localhost port=5432'
	DATA 'the_geom from ways as foo using unique gid using SRID=900913'
	CLASSITEM 'gid'
	TEMPLATE 'ausgabe.phtml'

	METADATA 
	'WMS_TITLE'   'streets' 
	'WMS_SRS'    "EPSG:900913"	
	'WMS_INCLUDE_ITEMS' 'all'	
	END 

	CLASS 
	TEXT ([gid],[source],[target])
	EXPRESSION /./

	STYLE 
	WIDTH 1
	COLOR 0 0 0
	END 

	LABEL 
		TYPE TRUETYPE 
		ANTIALIAS TRUE 
		FONT 'arial' 
		COLOR 0 0 0 
		BACKGROUNDCOLOR 240 240 240 
		 POSITION cc
		  MINSIZE 8
		MAXSIZE 12
	  	BUFFER 2
		 END 
	END 
	END

	LAYER 
	OFFSITE 255 255 255
	#LABELITEM 'name'
	TOLERANCE 20
	NAME		'dead_ends' 
	TYPE		POINT
	STATUS	DEFAULT
	CONNECTIONTYPE postgis
	CONNECTION 'user=postgres password=postgres dbname=routing host=localhost port=5432'
	DATA 'the_geom from vertices_tmp as foo using unique id using SRID=900913'


	CLASSITEM 'cnt'
	TEMPLATE 'ausgabe.phtml'

	METADATA 
	'WMS_TITLE'   'dead_ends' 
	'WMS_SRS'    "EPSG:900913"	
	'WMS_INCLUDE_ITEMS' 'all'	
	END 
	CLASS 
	Text ([id])
	EXPRESSION /1/
	STYLE 
	SYMBOL 'tent'
	SIZE 11
	COLOR 255 0 0
	END 

	LABEL 
		TYPE TRUETYPE 
		ANTIALIAS TRUE 
		FONT 'arial' 
		COLOR 255 0 0
		BACKGROUNDCOLOR 240 240 240 
		 POSITION cr
		  MINSIZE 8
		MAXSIZE 12
	  	BUFFER 2
		 END 
	END 

	CLASS 
	TEXT ([id])
	EXPRESSION /./

	STYLE 
	SYMBOL 'tent'
	SIZE 11
	COLOR 0 0 255
	END 

	LABEL 
		TYPE TRUETYPE 
		ANTIALIAS TRUE 
		FONT 'arial' 
		COLOR 0 0 255 
		BACKGROUNDCOLOR 240 240 240 
		 POSITION cr
		  MINSIZE 8
		MAXSIZE 12
	  	BUFFER 2
		 END 
	END 
	END
	END 

If you open your MapServer-testing-apllication via: http://localhost/cgi-bin/mapserv?map=/var/www/gastronomap_wms/gastronomap_routing.map

and you zoom in you get something like:

Everything fine with the data ! :-)

But if it looks like:

Definitely something went wrong........