pgr_lineGraphFull - Experimental

pgr_lineGraphFull — Transforms a given graph into a new graph where all of the vertices from the original graph are converted to line graphs.

Warning

Possible server crash

  • These functions might create a server crash

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

Availability

  • Version 2.6.0

    • New Experimental function

Description

pgr_lineGraphFull, converts original directed graph to a directed line graph by converting each vertex to a complete graph and keeping all the original edges. The new connecting edges have a cost 0 and go between the adjacent original edges, respecting the directionality.

A possible application of the resulting graph is “routing with two edge restrictions”:

  • Setting a cost of using the vertex when routing between edges on the connecting edge

  • Forbid the routing between two edges by removing the connecting edge

This is possible because each of the intersections (vertices) in the original graph are now complete graphs that have a new edge for each possible turn across that intersection.

The main characteristics are:

  • This function is for directed graphs.

  • Results are undefined when a negative vertex id is used in the input graph.

  • Results are undefined when a duplicated edge id is used in the input graph.

  • Running time: TBD

Signatures

Summary

pgr_lineGraphFull(Edges SQL)
RETURNS SET OF (seq, source, target, cost, edge)
OR EMPTY SET
Example:

Full line graph of subgraph of edges \(\{4, 7, 8, 10\}\)

SELECT * FROM pgr_lineGraphFull(
  $$SELECT id, source, target, cost, reverse_cost
  FROM edges
  WHERE id IN (4, 7, 8, 10)$$);
 seq | source | target | cost | edge
-----+--------+--------+------+------
   1 |     -1 |      7 |    1 |    4
   2 |      6 |     -1 |    0 |    0
   3 |     -2 |      6 |    1 |   -4
   4 |     -3 |      3 |    1 |   -7
   5 |     -4 |     11 |    1 |    8
   6 |     -5 |      8 |    1 |   10
   7 |      7 |     -2 |    0 |    0
   8 |      7 |     -3 |    0 |    0
   9 |      7 |     -4 |    0 |    0
  10 |      7 |     -5 |    0 |    0
  11 |     -6 |     -2 |    0 |    0
  12 |     -6 |     -3 |    0 |    0
  13 |     -6 |     -4 |    0 |    0
  14 |     -6 |     -5 |    0 |    0
  15 |     -7 |     -2 |    0 |    0
  16 |     -7 |     -3 |    0 |    0
  17 |     -7 |     -4 |    0 |    0
  18 |     -7 |     -5 |    0 |    0
  19 |     -8 |     -2 |    0 |    0
  20 |     -8 |     -3 |    0 |    0
  21 |     -8 |     -4 |    0 |    0
  22 |     -8 |     -5 |    0 |    0
  23 |     -9 |     -6 |    1 |    7
  24 |      3 |     -9 |    0 |    0
  25 |    -10 |     -7 |    1 |   -8
  26 |     11 |    -10 |    0 |    0
  27 |    -11 |     -8 |    1 |  -10
  28 |      8 |    -11 |    0 |    0
(28 rows)

Parameters

Parameter

Type

Description

Edges SQL

TEXT

Edges SQL as described below.

Inner Queries

Edges SQL

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)

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

Result Columns

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

Column

Type

Description

seq

INTEGER

Sequential value starting from 1.

  • Gives a local identifier for the edge

source

BIGINT

Identifier of the source vertex of the current edge.

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

target

BIGINT

Identifier of the target vertex of the current edge.

  • 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.

Additional Examples

The examples of this section are based on the Sample Data network. The examples include the subgraph including edges 4, 7, 8, and 10 with reverse_cost.

The data

This example displays how this graph transformation works to create additional edges for each possible turn in a graph.

SELECT id, source, target, cost, reverse_cost
FROM edges
WHERE id IN (4, 7, 8, 10);
 id | source | target | cost | reverse_cost
----+--------+--------+------+--------------
  4 |      6 |      7 |    1 |            1
  7 |      3 |      7 |    1 |            1
  8 |      7 |     11 |    1 |            1
 10 |      7 |      8 |    1 |            1
(4 rows)

first

The transformation

SELECT * FROM pgr_lineGraphFull(
  $$SELECT id, source, target, cost, reverse_cost
  FROM edges
  WHERE id IN (4, 7, 8, 10)$$);
 seq | source | target | cost | edge
-----+--------+--------+------+------
   1 |     -1 |      7 |    1 |    4
   2 |      6 |     -1 |    0 |    0
   3 |     -2 |      6 |    1 |   -4
   4 |     -3 |      3 |    1 |   -7
   5 |     -4 |     11 |    1 |    8
   6 |     -5 |      8 |    1 |   10
   7 |      7 |     -2 |    0 |    0
   8 |      7 |     -3 |    0 |    0
   9 |      7 |     -4 |    0 |    0
  10 |      7 |     -5 |    0 |    0
  11 |     -6 |     -2 |    0 |    0
  12 |     -6 |     -3 |    0 |    0
  13 |     -6 |     -4 |    0 |    0
  14 |     -6 |     -5 |    0 |    0
  15 |     -7 |     -2 |    0 |    0
  16 |     -7 |     -3 |    0 |    0
  17 |     -7 |     -4 |    0 |    0
  18 |     -7 |     -5 |    0 |    0
  19 |     -8 |     -2 |    0 |    0
  20 |     -8 |     -3 |    0 |    0
  21 |     -8 |     -4 |    0 |    0
  22 |     -8 |     -5 |    0 |    0
  23 |     -9 |     -6 |    1 |    7
  24 |      3 |     -9 |    0 |    0
  25 |    -10 |     -7 |    1 |   -8
  26 |     11 |    -10 |    0 |    0
  27 |    -11 |     -8 |    1 |  -10
  28 |      8 |    -11 |    0 |    0
(28 rows)

second

In the transformed graph, all of the edges from the original graph are still present (yellow), but we now have additional edges for every turn that could be made across vertex 7 (orange).

Creating table that identifies transformed vertices

The vertices in the transformed graph are each created by splitting up the vertices in the original graph. Unless a vertex in the original graph is a leaf vertex, it will generate more than one vertex in the transformed graph. One of the newly created vertices in the transformed graph will be given the same vertex identifier as the vertex that it was created from in the original graph, but the rest of the newly created vertices will have negative vertex ids.

Following is an example of how to generate a table that maps the ids of the newly created vertices with the original vertex that they were created from

Store edge results

The first step is to store the results of the pgr_lineGraphFull call into a table

SELECT seq AS id, source, target, cost, edge
INTO lineGraph_edges
FROM pgr_lineGraphFull(
  $$SELECT id, source, target, cost, reverse_cost
  FROM edges
  WHERE id IN (4, 7, 8, 10)$$);
SELECT 28

Create the mapping table

From the original graph’s vertex information

SELECT id, NULL::BIGINT original_id
INTO vertex_map
FROM vertices;
SELECT 17

Add the new vertices

INSERT INTO vertex_map (id)
(SELECT id
FROM pgr_extractVertices(
  $$SELECT id, source, target FROM lineGraph_edges$$) WHERE id < 0);
INSERT 0 11

Filling the mapping table

The positive vertex identifiers are the original identifiers

UPDATE vertex_map
SET original_id = id
WHERE id > 0;
UPDATE 17

Inspecting the vertices map

SELECT *
FROM vertex_map ORDER BY id DESC;
 id  | original_id
-----+-------------
  17 |          17
  16 |          16
  15 |          15
  14 |          14
  13 |          13
  12 |          12
  11 |          11
  10 |          10
   9 |           9
   8 |           8
   7 |           7
   6 |           6
   5 |           5
   4 |           4
   3 |           3
   2 |           2
   1 |           1
  -1 |
  -2 |
  -3 |
  -4 |
  -5 |
  -6 |
  -7 |
  -8 |
  -9 |
 -10 |
 -11 |
(28 rows)

The self loops happen when there is no cost traveling to the target and the source has an original value.

SELECT *, source AS targets_original_id
  FROM lineGraph_edges
  WHERE cost = 0 and source > 0;
 id | source | target | cost | edge | targets_original_id
----+--------+--------+------+------+---------------------
  2 |      6 |     -1 |    0 |    0 |                   6
  7 |      7 |     -2 |    0 |    0 |                   7
  8 |      7 |     -3 |    0 |    0 |                   7
  9 |      7 |     -4 |    0 |    0 |                   7
 10 |      7 |     -5 |    0 |    0 |                   7
 24 |      3 |     -9 |    0 |    0 |                   3
 26 |     11 |    -10 |    0 |    0 |                  11
 28 |      8 |    -11 |    0 |    0 |                   8
(8 rows)

Updating values from self loops

WITH
self_loops AS (
  SELECT DISTINCT source, target, source AS targets_original_id
  FROM lineGraph_edges
  WHERE cost = 0 and source > 0)
UPDATE vertex_map SET original_id = targets_original_id
FROM self_loops WHERE target = id;
UPDATE 8

Inspecting the vertices table

SELECT *
FROM vertex_map WHERE id < 0
ORDER BY id DESC;
 id  | original_id
-----+-------------
  -1 |           6
  -2 |           7
  -3 |           7
  -4 |           7
  -5 |           7
  -6 |
  -7 |
  -8 |
  -9 |           3
 -10 |          11
 -11 |           8
(11 rows)

Updating from inner self loops

WITH
assigned_vertices
AS (SELECT id, original_id
  FROM vertex_map
  WHERE original_id IS NOT NULL),
cross_edges
AS (SELECT DISTINCT e.source, v.original_id AS source_original_id
  FROM lineGraph_edges AS e
  JOIN vertex_map AS v ON (e.target = v.id)
  WHERE source NOT IN (SELECT id FROM assigned_vertices)
)
UPDATE vertex_map SET original_id = source_original_id
FROM cross_edges WHERE source = id;
UPDATE 3

Inspecting the vertices map

SELECT *
FROM vertex_map WHERE id < 0
ORDER BY id DESC;
 id  | original_id
-----+-------------
  -1 |           6
  -2 |           7
  -3 |           7
  -4 |           7
  -5 |           7
  -6 |           7
  -7 |           7
  -8 |           7
  -9 |           3
 -10 |          11
 -11 |           8
(11 rows)

Adding a soft restriction

A soft restriction going from vertex 6 to vertex 3 using edges 4 -> 7 is wanted.

Idenifying the restriction

Running a pgr_dijkstraNear - Proposed the edge with cost 0, edge 8, is where the cost will be increased

SELECT seq, path_seq, start_vid, end_vid, node, original_id, edge, cost, agg_cost
FROM (SELECT * FROM pgr_dijkstraNear(
  $$SELECT * FROM lineGraph_edges$$,
  (SELECT array_agg(id) FROM vertex_map where original_id = 6),
  (SELECT array_agg(id) FROM vertex_map where original_id = 3))) dn
JOIN vertex_map AS v1 ON (node = v1.id);
 seq | path_seq | start_vid | end_vid | node | original_id | edge | cost | agg_cost
-----+----------+-----------+---------+------+-------------+------+------+----------
   3 |        3 |        -1 |       3 |   -3 |           7 |    4 |    1 |        1
   1 |        1 |        -1 |       3 |   -1 |           6 |    1 |    1 |        0
   4 |        4 |        -1 |       3 |    3 |           3 |   -1 |    0 |        2
   2 |        2 |        -1 |       3 |    7 |           7 |    8 |    0 |        1
(4 rows)

The edge to be altered is WHERE cost = 0 AND seq != 1 AND edge != -1 from the previus query:

SELECT edge FROM pgr_dijkstraNear(
  $$SELECT * FROM lineGraph_edges$$,
  (SELECT array_agg(id) FROM vertex_map where original_id = 6),
  (SELECT array_agg(id) FROM vertex_map where original_id = 3))
WHERE cost = 0 AND seq != 1 AND edge != -1;
 edge
------
    8
(1 row)

Adding a value to the restriction

Updating the cost to the edge:

UPDATE lineGraph_edges
SET cost = 100
WHERE id IN (
SELECT edge FROM pgr_dijkstraNear(
  $$SELECT * FROM lineGraph_edges$$,
  (SELECT array_agg(id) FROM vertex_map where original_id = 6),
  (SELECT array_agg(id) FROM vertex_map where original_id = 3))
WHERE cost = 0 AND seq != 1 AND edge != -1);
UPDATE 1
Example:

Routing from \(6\) to \(3\)

Now the route does not use edge 8 and does a U turn on a leaf vertex.

WITH
results AS (
  SELECT * FROM pgr_dijkstraNear(
    $$SELECT * FROM lineGraph_edges$$,
    (SELECT array_agg(id) FROM vertex_map where original_id = 6),
    (SELECT array_agg(id) FROM vertex_map where original_id = 3)))
SELECT seq, path_seq, start_vid, end_vid, node, original_id, edge, cost, agg_cost
FROM results
LEFT JOIN vertex_map AS v1 ON (node = v1.id) ORDER BY seq;
 seq | path_seq | start_vid | end_vid | node | original_id | edge | cost | agg_cost
-----+----------+-----------+---------+------+-------------+------+------+----------
   1 |        1 |        -1 |       3 |   -1 |           6 |    1 |    1 |        0
   2 |        2 |        -1 |       3 |    7 |           7 |   10 |    0 |        1
   3 |        3 |        -1 |       3 |   -5 |           7 |    6 |    1 |        1
   4 |        4 |        -1 |       3 |    8 |           8 |   28 |    0 |        2
   5 |        5 |        -1 |       3 |  -11 |           8 |   27 |    1 |        2
   6 |        6 |        -1 |       3 |   -8 |           7 |   20 |    0 |        3
   7 |        7 |        -1 |       3 |   -3 |           7 |    4 |    1 |        3
   8 |        8 |        -1 |       3 |    3 |           3 |   -1 |    0 |        4
(8 rows)

Simplifying leaf vertices

In this example, there is no additional cost for traversing a leaf vertex.

Using the vertex map give the leaf verices their original value.

On the source column

WITH
u_turns AS (
SELECT e.id AS eid, v1.original_id
FROM linegraph_edges as e
JOIN vertex_map AS v1 ON (source = v1.id)
AND v1.original_id IN (3, 6, 8, 11))
UPDATE lineGraph_edges
SET source = original_id
FROM u_turns
WHERE id = eid;
UPDATE 8

On the target column

WITH
u_turns AS (
SELECT e.id AS eid, v1.original_id
FROM linegraph_edges as e
JOIN vertex_map AS v1 ON (target = v1.id)
AND v1.original_id IN (3, 6, 8, 11))
UPDATE lineGraph_edges
SET target = original_id
FROM u_turns
WHERE id = eid;
UPDATE 8

Removing self loops on leaf nodes

The self loops of the leaf nodes are

SELECT * FROM linegraph_edges
WHERE source = target
ORDER BY id;
 id | source | target | cost | edge
----+--------+--------+------+------
  2 |      6 |      6 |    0 |    0
 24 |      3 |      3 |    0 |    0
 26 |     11 |     11 |    0 |    0
 28 |      8 |      8 |    0 |    0
(4 rows)

Which can be removed

DELETE FROM linegraph_edges
WHERE source = target;
DELETE 4
Example:

Routing from \(6\) to \(3\)

Routing can be done now using the original vertices id using pgr_dijkstra

WITH
results AS (
  SELECT * FROM pgr_dijkstra(
    $$SELECT * FROM lineGraph_edges$$, 6, 3))
SELECT seq, path_seq, node, original_id, edge, cost, agg_cost
FROM results
LEFT JOIN vertex_map AS v1 ON (node = v1.id) ORDER BY seq;
 seq | path_seq | node | original_id | edge | cost | agg_cost
-----+----------+------+-------------+------+------+----------
   1 |        1 |    6 |           6 |    1 |    1 |        0
   2 |        2 |    7 |           7 |    9 |    0 |        1
   3 |        3 |   -4 |           7 |    5 |    1 |        1
   4 |        4 |   11 |          11 |   25 |    1 |        2
   5 |        5 |   -7 |           7 |   16 |    0 |        3
   6 |        6 |   -3 |           7 |    4 |    1 |        3
   7 |        7 |    3 |           3 |   -1 |    0 |        4
(7 rows)

Complete routing graph

Add edges from the original graph

Add all the edges that are not involved in the line graph process to the new table

SELECT id, source, target, cost, reverse_cost
INTO new_graph from edges
WHERE id NOT IN (4, 7, 8, 10);
SELECT 14

Some administrative tasks to get new identifiers for the edges

CREATE SEQUENCE new_graph_id_seq;
CREATE SEQUENCE
ALTER TABLE new_graph ALTER COLUMN id SET DEFAULT nextval('new_graph_id_seq');
ALTER TABLE
ALTER TABLE new_graph ALTER COLUMN id SET NOT NULL;
ALTER TABLE
ALTER SEQUENCE new_graph_id_seq OWNED BY new_graph.id;
ALTER SEQUENCE
SELECT setval('new_graph_id_seq', (SELECT max(id) FROM new_graph));
 setval
--------
     18
(1 row)

Add the newly calculated edges

INSERT INTO new_graph (source, target, cost, reverse_cost)
SELECT source, target, cost, -1 FROM lineGraph_edges;
INSERT 0 24

Using the routing graph

When using this method for routing with soft restrictions there will be uturns

Example:

Routing from \(6\) to \(3\)

WITH
results AS (
  SELECT * FROM pgr_dijkstra(
    $$SELECT * FROM new_graph$$, 6, 3))
SELECT seq, path_seq, node, original_id, edge, cost, agg_cost
FROM results
LEFT JOIN vertex_map AS v1 ON (node = v1.id) ORDER BY seq;
 seq | path_seq | node | original_id | edge | cost | agg_cost
-----+----------+------+-------------+------+------+----------
   1 |        1 |    6 |           6 |   35 |    1 |        0
   2 |        2 |    7 |           7 |   20 |    0 |        1
   3 |        3 |   -4 |           7 |   41 |    1 |        1
   4 |        4 |   11 |          11 |   37 |    1 |        2
   5 |        5 |   -7 |           7 |   27 |    0 |        3
   6 |        6 |   -3 |           7 |   40 |    1 |        3
   7 |        7 |    3 |           3 |   -1 |    0 |        4
(7 rows)

Example:

Routing from \(5\) to \(1\)

WITH
results AS (
  SELECT * FROM pgr_dijkstra(
    $$SELECT * FROM new_graph$$, 5, 1))
SELECT seq, path_seq, node, original_id, edge, cost, agg_cost
FROM results
LEFT JOIN vertex_map AS v1 ON (node = v1.id) ORDER BY seq;
 seq | path_seq | node | original_id | edge | cost | agg_cost
-----+----------+------+-------------+------+------+----------
   1 |        1 |    5 |           5 |    1 |    1 |        0
   2 |        2 |    6 |           6 |   35 |    1 |        1
   3 |        3 |    7 |           7 |   20 |    0 |        2
   4 |        4 |   -4 |           7 |   41 |    1 |        2
   5 |        5 |   11 |          11 |   37 |    1 |        3
   6 |        6 |   -7 |           7 |   27 |    0 |        4
   7 |        7 |   -3 |           7 |   40 |    1 |        4
   8 |        8 |    3 |           3 |    6 |    1 |        5
   9 |        9 |    1 |           1 |   -1 |    0 |        6
(9 rows)

See Also

Indices and tables