pgr_analyzeGraph

Name

pgr_anlizeGraph — Analyzes the network topology.

Synopsis

The function returns:

  • OK after the analysis has finished.
  • FAIL when the analysis was not completed due to an error.
varchar pgr_analyzeGraph(text edge_table, double precision tolerance,
                   text the_geom:='the_geom', text id:='id',
                   text source:='source',text target:='target',text rows_where:='true')

Description

Prerequisites

The edge table to be analyzed must contain a source column and a target column filled with id’s of the vertices of the segments and the corresponding vertices table <edge_table>_vertices_pgr that stores the vertices information.

Parameters

The analyze graph function accepts the following parameters:

edge_table:text Network table name. (may contain the schema name as well)
tolerance:float8 Snapping tolerance of disconnected edges. (in projection unit)
the_geom:text Geometry column name of the network table. Default value is the_geom.
id:text Primary key column name of the network table. Default value is id.
source:text Source column name of the network table. Default value is source.
target:text Target column name of the network table. Default value is target.
rows_where:text Condition to select a subset or rows. Default value is true to indicate all rows.

The function returns:

  • OK after the analysis has finished.
    • Uses the vertices table: <edge_table>_vertices_pgr.
    • Fills completly the cnt and chk columns of the vertices table.
    • Returns the analysis of the section of the network defined by rows_where
  • FAIL when the analysis was not completed due to an error.
    • The vertices table is not found.
    • 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 can be created with pgr_createVerticesTable or pgr_createTopology

The structure of the vertices table is:

id:bigint Identifier of the vertex.
cnt:integer Number of vertices in the edge_table that reference this vertex.
chk:integer Indicator that the vertex might have a problem.
ein:integer Number of vertices in the edge_table that reference this vertex as incoming. See pgr_analyzeOneway.
eout:integer Number of vertices in the edge_table that reference this vertex as outgoing. See pgr_analyzeOneway.
the_geom:geometry Point geometry of the vertex.

History

  • New in version 2.0.0

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

The simplest way to use pgr_analyzeGraph is:

SELECT  pgr_create_topology('edge_table',0.001);
SELECT  pgr_analyzeGraph('edge_table',0.001);

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

SELECT  pgr_analyzeGraph('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 mytable 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_analyzeGraph('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_analyzeGraph('edge_table',0.001,the_geom:='the_geom',id:='id',source:='source',target:='target');

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

Parameters defined with a default value can be ommited, as long as the value matches the default:

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

Selecting rows using rows_where parameter

Selecting rows based on the id. Displays the analysis a the section of the network.

SELECT  pgr_analyzeGraph('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_analyzeGraph('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_analyzeGraph('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, source AS src ,target AS tgt , the_geom AS mygeom FROM edge_table);
SELECT pgr_createTopology('mytable',0.001,'mygeom','gid','src','tgt');

Using positional notation:

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

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

Warning

An error would occur when the arguments are not given in the appropriate 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_analyzeGraph('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_analyzeGraph('mytable',0.001,the_geom:='mygeom',id:='gid',source:='src',target:='tgt');

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

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

SELECT  pgr_analyzeGraph('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 place=’myhouse’ of the table othertable. (note the use of quote_literal)

DROP TABLE IF EXISTS otherTable;
CREATE TABLE otherTable AS  (SELECT 'myhouse'::text AS place, st_point(2.5,2.5) AS other_geom) ;
SELECT  pgr_analyzeGraph('mytable',0.001,'mygeom','gid','src','tgt',
         rows_where:='mygeom && (SELECT st_buffer(other_geom,1) FROM otherTable WHERE place='||quote_literal('myhouse')||')');

SELECT  pgr_analyzeGraph('mytable',0.001,source:='src',id:='gid',target:='tgt',the_geom:='mygeom',
        rows_where:='mygeom && (SELECT st_buffer(other_geom,1) FROM otherTable WHERE place='||quote_literal('myhouse')||')');

Examples

    SELECT  pgr_create_topology('edge_table',0.001);
    SELECT pgr_analyzeGraph('edge_table', 0.001);
    NOTICE:  PROCESSING:
    NOTICE:  pgr_analyzeGraph('edge_table',0.001,'the_geom','id','source','target','true')
    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: 2
    NOTICE:                            Dead ends: 7
    NOTICE:  Potential gaps found near dead ends: 1
    NOTICE:               Intersections detected: 1
    NOTICE:                      Ring geometries: 0

     pgr_analizeGraph
    --------------------
     OK
    (1 row)

    SELECT  pgr_analyzeGraph('edge_table',0.001,rows_where:='id < 10');
    NOTICE:  PROCESSING:
    NOTICE:  pgr_analyzeGraph('edge_table',0.001,'the_geom','id','source','target','id < 10')
    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: 0
    NOTICE:                            Dead ends: 4
    NOTICE:  Potential gaps found near dead ends: 0
    NOTICE:               Intersections detected: 0
    NOTICE:                      Ring geometries: 0

     pgr_analizeGraph
    --------------------
     OK
    (1 row)

    SELECT  pgr_analyzeGraph('edge_table',0.001,rows_where:='id >= 10');
    NOTICE:  PROCESSING:
    NOTICE:  pgr_analyzeGraph('edge_table',0.001,'the_geom','id','source','target','id >= 10')
    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: 2
    NOTICE:                            Dead ends: 8
    NOTICE:  Potential gaps found near dead ends: 1
    NOTICE:               Intersections detected: 1
    NOTICE:                      Ring geometries: 0

     pgr_analizeGraph
    --------------------
     OK
    (1 row)

    -- Simulate removal of edges
    SELECT pgr_createTopology('edge_table', 0.001,rows_where:='id <17');
    SELECT pgr_analyzeGraph('edge_table', 0.001);
    NOTICE:  PROCESSING:
    NOTICE:  pgr_analyzeGraph('edge_table',0.001,'the_geom','id','source','target','true')
    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: 0
    NOTICE:                            Dead ends: 3
    NOTICE:  Potential gaps found near dead ends: 0
    NOTICE:               Intersections detected: 0
    NOTICE:                      Ring geometries: 0

     pgr_analizeGraph
    --------------------
     OK
    (1 row)
SELECT pgr_createTopology('edge_table', 0.001,rows_where:='id <17');
NOTICE:  PROCESSING:
NOTICE:  pgr_createTopology('edge_table',0.001,'the_geom','id','source','target','id <17')
NOTICE:  Performing checks, pelase wait .....
NOTICE:  Creating Topology, Please wait...
NOTICE:  -------------> TOPOLOGY CREATED FOR  16 edges
NOTICE:  Rows with NULL geometry or NULL id: 0
NOTICE:  Vertices table for table public.edge_table is: public.edge_table_vertices_pgr
NOTICE:  ----------------------------------------------

     pgr_analizeGraph
    --------------------
     OK
    (1 row)

SELECT pgr_analyzeGraph('edge_table', 0.001);
NOTICE:  PROCESSING:
NOTICE:  pgr_analyzeGraph('edge_table',0.001,'the_geom','id','source','target','true')
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: 0
NOTICE:                            Dead ends: 3
NOTICE:  Potential gaps found near dead ends: 0
NOTICE:               Intersections detected: 0
NOTICE:                      Ring geometries: 0

     pgr_analizeGraph
    --------------------
     OK
    (1 row)

The examples use the Sample Data network.

See Also