# pgRouting Manual (2.5)

## pgr_analyzeGraph

## Name

`pgr_analyzeGraph` — 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.

- Use pgr_createVerticesTable to create the vertices table.
- Use pgr_createTopology to create the topology and the vertices table.

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 completely 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_createTopology('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');
    NOTICE:  PROCESSING:
    NOTICE:  pgr_analyzeGraph('edge_table',0.001,'id','the_geom','source','target','true')
    NOTICE:  Performing checks, please wait ...
    NOTICE:  Got function st_srid(bigint) does not exist
    NOTICE:  ERROR: something went wrong when checking for SRID of id in table public.edge_table
    pgr_analyzegraph
    ------------------
      FAIL
    (1 row)

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 omitted, 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');
    NOTICE:  PROCESSING:
    NOTICE:  pgr_analyzeGraph('mytable',0.001,'gid','mygeom','src','tgt','true')
    NOTICE:  Performing checks, please wait ...
    NOTICE:  Got function st_srid(bigint) does not exist
    NOTICE:  ERROR: something went wrong when checking for SRID of gid in table public.mytable
    pgr_analyzegraph
    ------------------
      FAIL
    (1 row)

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_createTopology('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_analyzeGraph
        --------------------
         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_analyzeGraph
        --------------------
         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_analyzeGraph
        --------------------
         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_analyzeGraph
        --------------------
         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_analyzeGraph
        --------------------
         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_analyzeGraph
        --------------------
         OK
        (1 row)

The examples use the Sample Data network.

## See Also

- Routing Topology for an overview of a topology for routing algorithms.
- pgr_analyzeOneway to analyze directionality of the edges.
- pgr_createVerticesTable to reconstruct the vertices table based on the source and target information.
- pgr_nodeNetwork to create nodes to a not noded edge table.

Indices and tables

- Index
- Search Page