# pgr_createTopology¶

## Name¶

pgr_createTopology — Builds a network topology based on the geometry information.

## Synopsis¶

The function returns:

• OK after the network topology has been built and the vertices table created.
• FAIL when the network topology was not built due to an error.
varchar pgr_createTopology(text edge_table, double precision tolerance,
text the_geom:='the_geom', text id:='id',
text source:='source',text target:='target',
text rows_where:='true', boolean clean:=false)


## Description¶

Parameters

The topology creation function accepts the following parameters:

edge_table: text Network table name. (may contain the schema name AS well) float8 Snapping tolerance of disconnected edges. (in projection unit) text Geometry column name of the network table. Default value is the_geom. text Primary key column name of the network table. Default value is id. text Source column name of the network table. Default value is source. text Target column name of the network table. Default value is target. text Condition to SELECT a subset or rows. Default value is true to indicate all rows that where source or target have a null value, otherwise the condition is used. boolean Clean any previous topology. Default value is false.

Warning

The edge_table will be affected

• The source column values will change.

• The target column values will change.

• An index will be created, if it doesn’t exists, to speed up the process to the following columns:

• id
• the_geom
• source
• target

The function returns:

• OK after the network topology has been built.
• Creates a vertices table: <edge_table>_vertices_pgr.
• Fills id and the_geom columns of the vertices table.
• Fills the source and target columns of the edge table referencing the id of the vertices table.
• FAIL when the network topology was not built due to an error:
• A required column of the Network table is not found or is not of the appropriate type.
• The condition is not well formed.
• The names of source , target or id are the same.
• The SRID of the geometry could not be determined.

The Vertices Table

The vertices table is a requirment of the pgr_analyzeGraph and the pgr_analyzeOneway functions.

The structure of the vertices table is:

id: bigint Identifier of the vertex. integer Number of vertices in the edge_table that reference this vertex. See pgr_analyzeGraph. integer Indicator that the vertex might have a problem. See pgr_analyzeGraph. integer Number of vertices in the edge_table that reference this vertex AS incoming. See pgr_analyzeOneway. integer Number of vertices in the edge_table that reference this vertex AS outgoing. See pgr_analyzeOneway. geometry Point geometry of the vertex.

History

• Renamed in version 2.0.0

## Usage when the edge table’s columns MATCH the default values:¶

The simplest way to use pgr_createtopology is:

SELECT  pgr_createTopology('edge_table',0.001);


When the arguments are given in the order described in the parameters:

SELECT  pgr_createTopology('edge_table',0.001,'the_geom','id','source','target');


We get the same result AS the simplest way to use the function.

Warning

An error would occur when the arguments are not given in the appropriate order: In this example, the column id of the table ege_table is passed to the function AS the geometry column, and the geometry column the_geom is passed to the function AS the id column.
SELECT  pgr_createTopology('edge_table',0.001,'id','the_geom','source','target');
ERROR: Can not determine the srid of the geometry “id” in table public.edge_table

When using the named notation

The order of the parameters do not matter:

SELECT  pgr_createTopology('edge_table',0.001,the_geom:='the_geom',id:='id',source:='source',target:='target');

SELECT  pgr_createTopology('edge_table',0.001,source:='source',id:='id',target:='target',the_geom:='the_geom');


Parameters defined with a default value can be omited, AS long AS the value matches the default:

SELECT  pgr_createTopology('edge_table',0.001,source:='source');


Selecting rows using rows_where parameter

Selecting rows based on the id.

SELECT  pgr_createTopology('edge_table',0.001,rows_where:='id < 10');


Selecting the rows where the geometry is near the geometry of row with id =5 .

SELECT  pgr_createTopology('edge_table',0.001,rows_where:='the_geom && (SELECT st_buffer(the_geom,0.05) FROM edge_table WHERE id=5)');


Selecting the rows where the geometry is near the geometry of the row with gid =100 of the table othertable.

DROP TABLE IF EXISTS otherTable;
CREATE TABLE otherTable AS  (SELECT 100 AS gid, st_point(2.5,2.5) AS other_geom);
SELECT  pgr_createTopology('edge_table',0.001,rows_where:='the_geom && (SELECT st_buffer(other_geom,1) FROM otherTable WHERE gid=100)');


## Usage when the edge table’s columns DO NOT MATCH the default values:¶

For the following table

DROP TABLE IF EXISTS mytable;
CREATE TABLE mytable AS (SELECT id AS gid, the_geom AS mygeom,source AS src ,target AS tgt FROM edge_table) ;


Using positional notation:

The arguments need to be given in the order described in the parameters:

SELECT  pgr_createTopology('mytable',0.001,'mygeom','gid','src','tgt');


Warning

An error would occur when the arguments are not given in the appropiriate order: In this example, the column gid of the table mytable is passed to the function AS the geometry column, and the geometry column mygeom is passed to the function AS the id column.
SELECT  pgr_createTopology('mytable',0.001,'gid','mygeom','src','tgt');
ERROR: Can not determine the srid of the geometry “gid” in table public.mytable

When using the named notation

The order of the parameters do not matter:

SELECT  pgr_createTopology('mytable',0.001,the_geom:='mygeom',id:='gid',source:='src',target:='tgt');

SELECT  pgr_createTopology('mytable',0.001,source:='src',id:='gid',target:='tgt',the_geom:='mygeom');


In this scenario omitting a parameter would create an error because the default values for the column names do not match the column names of the table.

Selecting rows using rows_where parameter

Selecting rows based on the id.

SELECT  pgr_createTopology('mytable',0.001,'mygeom','gid','src','tgt',rows_where:='gid < 10');

SELECT  pgr_createTopology('mytable',0.001,source:='src',id:='gid',target:='tgt',the_geom:='mygeom',rows_where:='gid < 10');


Selecting the rows where the geometry is near the geometry of row with id =5 .

SELECT  pgr_createTopology('mytable',0.001,'mygeom','gid','src','tgt',
rows_where:='mygeom && (SELECT st_buffer(mygeom,1) FROM mytable WHERE gid=5)');

SELECT  pgr_createTopology('mytable',0.001,source:='src',id:='gid',target:='tgt',the_geom:='mygeom',
rows_where:='mygeom && (SELECT st_buffer(mygeom,1) FROM mytable WHERE gid=5)');


Selecting the rows where the geometry is near the geometry of the row with gid =100 of the table othertable.

DROP TABLE IF EXISTS otherTable;
CREATE TABLE otherTable AS  (SELECT 100 AS gid, st_point(2.5,2.5) AS other_geom) ;
SELECT  pgr_createTopology('mytable',0.001,'mygeom','gid','src','tgt',
rows_where:='mygeom && (SELECT st_buffer(other_geom,1) FROM otherTable WHERE gid=100)');

SELECT  pgr_createTopology('mytable',0.001,source:='src',id:='gid',target:='tgt',the_geom:='mygeom',
rows_where:='mygeom && (SELECT st_buffer(other_geom,1) FROM otherTable WHERE gid=100)');


## Examples¶

SELECT pgr_createTopology('edge_table', 0.001,rows_where:='id<10');
NOTICE:  PROCESSING:
NOTICE:  pgr_createTopology('edge_table',0.0001,'the_geom','id','source','target','id<10')
NOTICE:  Performing checks, pelase wait .....
NOTICE:  -------------> TOPOLOGY CREATED FOR  9 edges
NOTICE:  Rows with NULL geometry or NULL id: 0
NOTICE:  Vertices table for table public.edge_table is: public.edge_table_vertices_pgr

pgr_createtopology
--------------------
OK
(1 row)

SELECT pgr_createTopology('edge_table', 0.001);
NOTICE:  PROCESSING:
NOTICE:  pgr_createTopology('edge_table',0.0001,'the_geom','id','source','target','true')
NOTICE:  Performing checks, pelase wait .....