pgr_lineGraph - Experimental

pgr_lineGraph — Transforms a given graph into its corresponding edge-based graph.

_images/boost-inside.jpeg

Boost Graph Inside

Warning

Experimental functions

  • They are not officially of the current release.
  • They likely will not be officially be part of the next release:
    • The functions might not make use of ANY-INTEGER and ANY-NUMERICAL
    • Name might change.
    • Signature might change.
    • Functionality might change.
    • pgTap tests might be missing.
    • Might need c/c++ coding.
    • May lack documentation.
    • Documentation if any might need to be rewritten.
    • Documentation examples might need to be automatically generated.
    • Might need a lot of feedback from the comunity.
    • Might depend on a proposed function of pgRouting
    • Might depend on a deprecated function of pgRouting

Synopsis

Given a graph G, its line graph L(G) is a graph such that:-

  • each vertex of L(G) represents an edge of G
  • two vertices of L(G) are adjacent if and only if their corresponding edges share a common endpoint in G.

The following figures show a graph (left, with blue vertices) and its Line Graph (right, with green vertices).

first

Signature Summary

pgr_lineGraph(edges_sql, directed)
RETURNS SET OF (seq, source, target, cost, reverse_cost)
    OR EMPTY SET

Signatures

Minimal signature

pgr_lineGraph(edges_sql)
RETURNS SET OF (seq, source, target, cost, reverse_cost) or EMPTY SET

The minimal signature is for a directed graph:

Example: 
SELECT * FROM pgr_lineGraph(
    'SELECT id, source, target, cost, reverse_cost FROM edge_table'
);
 seq | source | target | cost | reverse_cost
-----+--------+--------+------+--------------
   1 |    -18 |     18 |    1 |            1
   2 |    -17 |     17 |    1 |            1
   3 |    -16 |     -3 |    1 |           -1
   4 |    -16 |     16 |    1 |            1
   5 |    -15 |     -9 |    1 |            1
   6 |    -15 |     15 |    1 |            1
   7 |    -14 |    -10 |    1 |            1
   8 |    -14 |     12 |    1 |           -1
   9 |    -14 |     14 |    1 |            1
  10 |    -10 |     -7 |    1 |            1
  11 |    -10 |     -4 |    1 |            1
  12 |    -10 |      8 |    1 |            1
  13 |    -10 |     10 |    1 |            1
  14 |     -9 |     -8 |    1 |            1
  15 |     -9 |      9 |    1 |            1
  16 |     -9 |     11 |    1 |           -1
  17 |     -8 |     -7 |    1 |            1
  18 |     -8 |     -4 |    1 |            1
  19 |     -8 |      8 |    1 |            1
  20 |     -7 |     -6 |    1 |            1
  21 |     -6 |      6 |    1 |            1
  22 |     -4 |     -1 |    1 |            1
  23 |     -4 |      4 |    1 |            1
  24 |     -3 |     -2 |    1 |           -1
  25 |     -3 |      5 |    1 |           -1
  26 |     -2 |     -1 |    1 |           -1
  27 |     -2 |      4 |    1 |           -1
  28 |     -1 |      1 |    1 |            1
  29 |      5 |     -8 |    1 |           -1
  30 |      5 |      9 |    1 |           -1
  31 |      5 |     11 |    1 |           -1
  32 |      7 |     -7 |    1 |            1
  33 |      7 |     -4 |    1 |            1
  34 |      8 |     11 |    1 |           -1
  35 |     10 |     12 |    1 |           -1
  36 |     11 |     13 |    1 |           -1
  37 |     12 |     13 |    1 |           -1
  38 |     13 |    -15 |    1 |           -1
  39 |     16 |     -9 |    1 |            1
  40 |     16 |     15 |    1 |            1
(40 rows)

Complete Signature

pgr_lineGraph(edges_sql, directed);
RETURNS SET OF (seq, source, target, cost, reverse_cost) or EMPTY SET
This signature returns the Line Graph of the current graph:
  • on a directed graph when directed flag is missing or is set to true.
  • on an undirected graph when directed flag is set to false.
Example: 
SELECT * FROM pgr_lineGraph(
    'SELECT id, source, target, cost, reverse_cost FROM edge_table',
    FALSE
);
 seq | source | target | cost | reverse_cost
-----+--------+--------+------+--------------
   1 |     -3 |     -2 |    1 |           -1
   2 |     -3 |      5 |    1 |           -1
   3 |     -2 |      4 |    1 |           -1
   4 |      1 |      4 |    1 |           -1
   5 |      4 |      8 |    1 |           -1
   6 |      4 |     10 |    1 |           -1
   7 |      5 |      9 |    1 |           -1
   8 |      5 |     11 |    1 |           -1
   9 |      6 |      7 |    1 |           -1
  10 |      7 |      8 |    1 |           -1
  11 |      7 |     10 |    1 |           -1
  12 |      8 |      9 |    1 |           -1
  13 |      8 |     11 |    1 |           -1
  14 |      9 |     15 |    1 |           -1
  15 |     10 |     12 |    1 |           -1
  16 |     10 |     14 |    1 |           -1
  17 |     11 |     13 |    1 |           -1
  18 |     12 |     13 |    1 |           -1
  19 |     16 |     15 |    1 |           -1
(19 rows)

Description of the Signatures

Description of the edges_sql query for dijkstra like functions

edges_sql:an SQL query, which should return a set of rows with the following columns:
Column Type Default Description
id ANY-INTEGER   Identifier of the edge.
source ANY-INTEGER   Identifier of the first end point vertex of the edge.
target ANY-INTEGER   Identifier of the second end point vertex of the edge.
cost ANY-NUMERICAL  

Weight of the edge (source, target)

  • When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost ANY-NUMERICAL -1

Weight of the edge (target, source),

  • When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

Where:

ANY-INTEGER:SMALLINT, INTEGER, BIGINT
ANY-NUMERICAL:SMALLINT, INTEGER, BIGINT, REAL, FLOAT

Description of the parameters of the signatures

Column Type Description
edges_sql TEXT SQL query as described above.
directed BOOLEAN
  • When true the graph is considered as Directed.
  • When false the graph is considered as Undirected.

Description of the return values

RETURNS SETOF (seq, source, target, cost, reverse_cost)

Column Type Description
seq INTEGER Sequential value starting from 1.
source BIGINT

Identifier of the source vertex of the current edge id.

  • When negative: the source is the reverse edge in the original graph.
target BIGINT

Identifier of the target vertex of the current edge id.

  • When negative: the target is the reverse edge in the original graph.
cost FLOAT

Weight of the edge (source, target).

  • When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost FLOAT

Weight of the edge (target, source).

  • When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

See Also

Indices and tables