pgr_degree – Proposed¶
pgr_degree — For each vertex in an undirected graph, return the count of edges incident to the vertex.
Advertencia
Funciones propuestas para la próxima versión mayor.
No están oficialmente en la versión actual.
Es probable que oficialmente formen parte del próximo lanzamiento:
Las funciones hacen uso de ENTEROS y FLOTANTES
Probablemente el nombre no cambie. (Pero todavía puede)
Es posible que la firma no cambie. (Pero todavía puede)
Probablemente la funcionalidad no cambie. (Pero todavía puede)
Se han hecho pruebas con pgTap. Pero tal vez se necesiten más.
Es posible que la documentación necesite un refinamiento.
Disponibilidad
Versión 3.4.0
Nueva función propuesta
Descripción¶
Calculates the degree of the vertices of an undirected graph
Firmas¶
(node, degree)- Ejemplo:
Extraer la información del vértice
pgr_degree can utilize output from pgr_extractVertices or can have pgr_extractVertices embedded in the call. For decent size networks, it is best to prep your vertices table before hand and use that vertices table for pgr_degree calls.
DROP TABLE IF EXISTS tmp_edges_vertices_pgr;
NOTICE: table "tmp_edges_vertices_pgr" does not exist, skipping
DROP TABLE
CREATE TEMP TABLE tmp_edges_vertices_pgr AS
SELECT id, in_edges, out_edges
FROM pgr_extractVertices('SELECT id, geom FROM edges');
SELECT 17
SELECT * FROM pgr_degree(
$$SELECT id FROM edges$$,
$$SELECT id, in_edges, out_edges
FROM tmp_edges_vertices_pgr$$);
node | degree
------+--------
1 | 1
2 | 1
3 | 2
4 | 1
5 | 1
6 | 3
7 | 4
8 | 3
9 | 1
10 | 3
11 | 4
12 | 3
13 | 1
14 | 1
15 | 2
16 | 3
17 | 2
(17 rows)
Parámetros¶
Parámetro |
Tipo |
Descripción |
|---|---|---|
|
SQL de aristas como se describe a continuación |
|
|
Vertex SQL como se describe abajo |
Parámetros opcionales¶
Parámetro |
Tipo |
x Defecto |
Descripción |
|---|---|---|---|
|
|
|
|
Consultas Internas¶
SQL aristas¶
Columna |
Tipo |
Descripción |
|---|---|---|
|
|
Identificador de la arista. |
Vertex SQL¶
Columna |
Tipo |
Descripción |
|---|---|---|
|
|
Identificador del primer vértice de la arista. |
|
|
Arreglo de identificadores de las aristas que tienen el vértice
|
|
|
Arreglo de identificadores de las aristas que tienen el vértice
|
Columnas de resultados¶
Columna |
Tipo |
Descripción |
|---|---|---|
|
|
Identificador de vértice |
|
|
Number of edges that are incident to the vertex |
Ejemplos Adicionales¶
Degree of a sub graph¶
SELECT * FROM pgr_degree(
$$SELECT id FROM edges WHERE id < 17$$,
$$SELECT id, in_edges, out_edges
FROM pgr_extractVertices('SELECT id, geom FROM edges')$$);
node | degree
------+--------
1 | 1
2 | 0
3 | 2
4 | 0
5 | 1
6 | 3
7 | 4
8 | 3
9 | 1
10 | 3
11 | 4
12 | 3
13 | 0
14 | 0
15 | 2
16 | 3
17 | 2
(17 rows)
Ejecución de prueba¶
Para obtener la consulta generada que se usa para obtener la información de vértices, utilizar dryrun := true.
Los resultados se pueden usar como código base para realizar un refinamiento basado en las necesidades de desarrollo de back-end.
SELECT * FROM pgr_degree(
$$SELECT id FROM edges WHERE id < 17$$,
$$SELECT id, in_edges, out_edges
FROM pgr_extractVertices('SELECT id, geom FROM edges')$$,
dryrun => true);
NOTICE:
WITH
-- a sub set of edges of the graph goes here
g_edges AS (
SELECT id FROM edges WHERE id < 17
),
-- sub set of vertices of the graph goes here
all_vertices AS (
SELECT id, in_edges, out_edges
FROM pgr_extractVertices('SELECT id, geom FROM edges')
),
g_vertices AS (
SELECT id,
unnest(
coalesce(in_edges::BIGINT[], '{}'::BIGINT[])
||
coalesce(out_edges::BIGINT[], '{}'::BIGINT[])) AS eid
FROM all_vertices
),
totals AS (
SELECT v.id, count(*)
FROM g_vertices AS v
JOIN g_edges AS e ON (e.id = eid) GROUP BY v.id
)
SELECT id::BIGINT, coalesce(count, 0)::BIGINT FROM all_vertices LEFT JOIN totals USING (id)
;
node | degree
------+--------
(0 rows)
Degree from an existing table¶
If you have a vertices table already built using pgr_extractVertices
and want the degree of the whole graph rather than a subset, you can forgo using pgr_degree
and work with the in_edges and out_edges columns directly.
Callejones sin salida¶
To get the dead ends:
SELECT id FROM vertices
WHERE array_length(in_edges || out_edges, 1) = 1;
id
----
1
5
9
13
14
2
4
(7 rows)
That information is correct, for example, when the dead end is on the limit of the imported graph.
Visually node \(4\) looks to be as start/ending of 3 edges, but it is not.
Is that correct?
Is there such a small curb:
That does not allow a vehicle to use that visual intersection?
Is the application for pedestrians and therefore the pedestrian can easily walk on the small curb?
Is the application for the electricity and the electrical lines than can easily be extended on top of the small curb?
Is there a big cliff and from eagles view look like the dead end is close to the segment?
When there are many dead ends, to speed up, the Contraction - Familia de funciones functions can be used to divide the problem.
Linear edges¶
To get the linear edges:
SELECT id FROM vertices
WHERE array_length(in_edges || out_edges, 1) = 2;
id
----
3
15
17
(3 rows)
This information is correct, for example, when the application is taking into account speed bumps, stop signals.
When there are many linear edges, to speed up, the Contraction - Familia de funciones functions can be used to divide the problem.
Ver también¶
Índices y tablas