# pgRouting Manual (3.6)

## pgr_analyzeOneWay

`pgr_analyzeOneWay` — Analyzes oneway Sstreets and identifies flipped segments.

This function analyzes oneway streets in a graph and identifies any flipped segments.

Availability

- Version 2.0.0

  - Official function

## Description

The analyses of one way segments is pretty simple but can be a powerful tools to identifying some the potential problems created by setting the direction of a segment the wrong way. A node is a source if it has edges the exit from that node and no edges enter that node. Conversely, a node is a sink if all edges enter the node but none exit that node. For a source type node it is logically impossible to exist because no vehicle can exit the node if no vehicle and enter the node. Likewise, if you had a sink node you would have an infinite number of vehicle piling up on this node because you can enter it but not leave it.

So why do we care if the are not feasible? Well if the direction of an edge was reversed by mistake we could generate exactly these conditions. Think about a divided highway and on the north bound lane one segment got entered wrong or maybe a sequence of multiple segments got entered wrong or maybe this happened on a round-about. The result would be potentially a source and/or a sink node.

So by counting the number of edges entering and exiting each node we can identify both source and sink nodes so that you can look at those areas of your network to make repairs and/or report the problem back to your data vendor.

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.

## Signatures

pgr_analyzeOneWay(geom_table, s_in_rules, s_out_rules, t_in_rules, t_out_rules, [options])
options: `[oneway, source, target, two_way_if_null]`
RETURNS `TEXT`

## Parameters

edge_table:

  `text` Network table name. (may contain the schema name as well)

s_in_rules:

  `text[]` source node in rules

s_out_rules:

  `text[]` source node out rules

t_in_rules:

  `text[]` target node in rules

t_out_rules:

  `text[]` target node out rules

oneway:

  `text` oneway column name name of the network table. Default value is `oneway`.

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`.

two_way_if_null:

  `boolean` flag to treat oneway NULL values as bi-directional. Default value is `true`.

Note

It is strongly recommended to use the named notation. See pgr_createVerticesTable or pgr_createTopology for examples.

The function returns:

- `OK` after the analysis has finished.

  - Uses the vertices table: <edge_table>_vertices_pgr.

  - Fills completely the `ein` and `eout` columns of the vertices table.

- `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 names of source , target or oneway are the same.

The rules are defined as an array of text strings that if match the `oneway` value would be counted as `true` for the source or target in or out condition.

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. See pgr_analyzeGgraph.

chk:

  `integer` Indicator that the vertex might have a problem. See pgr_analyzeGraph.

ein:

  `integer` Number of vertices in the edge_table that reference this vertex as incoming.

eout:

  `integer` Number of vertices in the edge_table that reference this vertex as outgoing.

the_geom:

  `geometry` Point geometry of the vertex.

## Additional Examples

    ALTER TABLE edges ADD COLUMN dir TEXT;
    ALTER TABLE
    SELECT  pgr_createTopology('edges', 0.001, 'geom');
    NOTICE:  PROCESSING:
    NOTICE:  pgr_createTopology('edges', 0.001, 'geom', 'id', 'source', 'target', rows_where := 'true', clean := f)
    NOTICE:  Performing checks, please wait .....
    NOTICE:  Creating Topology, Please wait...
    NOTICE:  -------------> TOPOLOGY CREATED FOR  0 edges
    NOTICE:  Rows with NULL geometry or NULL id: 0
    NOTICE:  Vertices table for table public.edges is: public.edges_vertices_pgr
    NOTICE:  ----------------------------------------------
     pgr_createtopology
    --------------------
     OK
    (1 row)

    UPDATE edges SET
    dir = CASE WHEN (cost>0 AND reverse_cost>0) THEN 'B'   /* both ways */
               WHEN (cost>0 AND reverse_cost<0) THEN 'FT'  /* direction of the LINESSTRING */
               WHEN (cost<0 AND reverse_cost>0) THEN 'TF'  /* reverse direction of the LINESTRING */
               ELSE '' END;
    UPDATE 18
    /* unknown */
    	SELECT pgr_analyzeOneWay('edges',
            ARRAY['', 'B', 'TF'],
            ARRAY['', 'B', 'FT'],
            ARRAY['', 'B', 'FT'],
            ARRAY['', 'B', 'TF'],
            oneway:='dir');
    NOTICE:  PROCESSING:
    NOTICE:  pgr_analyzeOneway('edges','{"",B,TF}','{"",B,FT}','{"",B,FT}','{"",B,TF}','dir','source','target',t)
    NOTICE:  Analyzing graph for one way street errors.
    NOTICE:  Analysis 25% complete ...
    NOTICE:  Analysis 50% complete ...
    NOTICE:  Analysis 75% complete ...
    NOTICE:  Analysis 100% complete ...
    NOTICE:  Found 0 potential problems in directionality
     pgr_analyzeoneway
    -------------------
     OK
    (1 row)

## See Also

- Topology - Family of Functions

- pgr_analyzeGraph

- pgr_createVerticesTable

- Sample Data

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