Hi George, There is a simple example of a script using topology on the wiki at: http://trac.osgeo.org/postgis/wiki/UsersWikiTopologyExample & more help at http://trac.osgeo.org/postgis/wiki/UsersWikiPostgisTopology
The attached script was written to take the New Zealand mainland coastline
comprised of various linestrings which had small gaps between them in some
cases, & build a polygon from them. To do this it iterated through the
linestrings, loading them into the topology one at a time with a small snapping
distance to ensure all the start/end nodes aligned correctly.
It also loads data from various shapefiles of island polygons into the table &
exports a shapefile of the entire national coastline as polygons. I think you
can pull out the appropriate SQL commands from this to do what you are asking
about.
I haven't tried this with multilinestrings, only single linestrings.
If you need additional help, feel free to ask, though I'm just learning the
topology stuff myself.
Cheers,
Brent Wood
--- On Wed, 5/16/12, george wash <gws...@hotmail.com> wrote:
From: george wash <gws...@hotmail.com>
Subject: Re: [postgis-users] Closing polylines
To: pcr...@pcreso.com
Date: Wednesday, May 16, 2012, 12:28 PM
On 5/16/2012 4:16 AM, pcr...@pcreso.com wrote:
You can work around
this problem by using the Postgis topology capability. It
will build polygons (faces) from such lines which you can
use as topopolygons or extract as conventional geometries.
--- On Tue, 5/15/12, george wash <gws...@hotmail.com>
wrote:
thank you pcreso, I had a look at the topology
section of the PostGIS manual, but I must admit I am going
to need some guidance as to how to proceed as I never used it
before.
Given the attachment in my earlier post, which is a dump of a simple
geometry table in the public schema, how do you suggest I proceed
with creating the topology and how do I then extract the closed
contours from it? Many thanks
mk_coast
Description: Binary data
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