[postgis-users] flow analysis

[Hugues François]

Hello,
 
You may try to work with a dump of your multi into single (st_dump(geom)).geom
 
Hugues.
 
 

________________________________

From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Jonatan Malaver
Sent: Thursday, May 16, 2013 2:01 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] flow analysis



OK, so after some research I found out that ST_StartPoint() returns NULL for multilinestring. Anyone know a work around?

 

Thanks,

 

Jonatan

 

From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Jonatan Malaver
Sent: Thursday, May 16, 2013 7:46 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] flow analysis

 

Here's my query

WITH RECURSIVE flow(gid, geom) AS (

    SELECT gid, geom FROM l4_3 WHERE gid = 212

  UNION ALL

    SELECT n.gid, n.geom

    FROM l4_3 n, flow f

    WHERE ST_DWithin(ST_EndPoint(f.geom),ST_StartPoint(n.geom),0.01)

  )

SELECT gid, ST_AsText(geom)

FROM flow;

 

Here's the result

212;"MULTILINESTRING((589700.21 2926252.04,589698.873744219 2926256.62316697))"

 

l4_3 is a multilinestring of and electrical circuit. I would like to see what's downstream the grid from a transformer, fuse, or upstream from a house meter.

 

Thanks,

 

Jonatan 

 

From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Nicolas Ribot
Sent: Wednesday, May 15, 2013 12:55 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] flow analysis

 

Hello,

 

This precise example, no, but the "WITH RECURSIVE" construct yes.

 

Could you post your query and the data model ?

 

Nicolas

 

On 15 May 2013 17:56, Jonatan Malaver <jon.malaver at shrewsburyma.gov> wrote:

	Hello again, 

	I tried the example, but it only returns the same line. Has anyone tried that example?

	 

	Thanks,

	 

	Jonatan 

	 

	From: postgis-users-bounces at lists.osgeo.org [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Nicolas Ribot
	Sent: Tuesday, May 14, 2013 1:02 PM
	To: PostGIS Users Discussion

	
	Subject: Re: [postgis-users] flow analysis

	 

	Hi,

	 

	The WITH RECURSIVE construct allows to walk a graph:

	 

	This link may help:

	http://blog.cleverelephant.ca/2010/07/network-walking-in-postgis.html

	 

	Nicolas

	 

	On 14 May 2013 18:40, Jonatan Malaver <jon.malaver at shrewsburyma.gov> wrote:

		Hello, is it possible to do any flow analysis? For example, query postgis for what down flow a certain point?

		 

		Thanks,

		 

		Jonatan Malaver

		 

		
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