Would you happen to have a hint to how to delete such components from a network/topology?
my proposal:
-create “components_table”
-insert new column (“component” id ) to the edge_table ( and fill from components_table )
- calculate sum(cost ) by component … and find the long tails
- filter OR delete by small component id-s ( I prefer creating new edge table instead of delete … )
– public.edge_table
– https://docs.pgrouting.org/3.1/en/sampledata.html
CREATE TABLE components_table as
SELECT * FROM pgr_connectedComponents(
‘SELECT id, source, target, cost, reverse_cost FROM edge_table’
)
;
– add a new column to the edge_table
ALTER TABLE edge_table ADD COLUMN component BIGINT;
UPDATE edge_table as e
SET component = c.component
FROM components_table c
WHERE (e.component is NULL) AND e.source=c.node
;
– calculate small component → sum(cost)
CREATE TABLE small_components as
SELECT component,
sum(cost) as sum_cost
FROM edge_table
GROUP BY 1
HAVING sum(cost) < 2 ;
– create new_edge_table
– filtering: not in small components
CREATE TABLE new_edge_table as
SELECT * FROM edge_table
WHERE component not in ( SELECT component FROM small_components )
ORDER BY id
;
the small_components tables
select * from small_components;
component | sum_cost
-----------±---------
14 | 1
16 | 1
(2 rows)
all components:
SELECT component,
sum(cost) as sum_cost
FROM edge_table
GROUP BY 1
ORDER BY 2 DESC ;
component | sum_cost
-----------±---------
1 | 12
14 | 1
16 | 1
(3 rows)
In your case … probably the cost is "in meter length "
ps:
Regards,
Imre
Hans Skov-Petersen <hsp@ign.ku.dk> ezt írta (időpont: 2021. jún. 27., V, 23:17):
Hi Imre
It seems like something I can make work to identify small subnets/components. Thanks.
Would you happen to have a hint to how to delete such components from a network/topology?
Cheers
Hans
From: Pgrouting-users <pgrouting-users-bounces@lists.osgeo.org> On Behalf Of Imre Samu
Sent: 27. juni 2021 22:59
To: pgRouting users mailing list <pgrouting-users@lists.osgeo.org>
Cc: pgRouting developers mailing list <pgrouting-dev@lists.osgeo.org>
Subject: Re: [pgrouting-users] Dangling sub-networks
Is there a way to identify (and potentially delete) such minor sub-nets?
IMHO: this is similar for detecting “Component” ( https://en.wikipedia.org/wiki/Component_(graph_theory) )
Have you checked the https://docs.pgrouting.org/3.1/en/components-family.html functions?
If you know the components - you can calculate the aggregated length of edges for each component.
Regards,
Imre
Hans Skov-Petersen <hsp@ign.ku.dk> ezt írta (időpont: 2021. jún. 27., V, 21:42):
Hi list
I realize that the network (OSM) I am working on is not always connected as it should (big surprise J)…. Some parts are disjoint from the rest – even when not being situated on islands, or other places where a disjoint is expected. Accordingly, routes from nodes on such sub-nets cannot be generated.
Is there a way to identify (and potentially delete) such minor sub-nets? For instance by asking for the aggregated length of edges of a sub-net.
Hans Skov-Petersen
Professor of Geoinformatics
University of Copenhagen
Department of Geosciences and Natural Resource Management
Section of Landscape Architecture and Planning
Rolighedsvej 23
DK-1958 Frederiksberg
DIR +45 35 33 18 16
MOB +45 23 82 80 45
hsp@ign.ku.dk
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