Thanks again for a prompt reply. QGIS is showing the results of the inserts & polygonise in the attached image. So, yes, just as you sketched it.
I had assumed Polygonize was constructing polygon TopoGeometries ?? Obviously I've missed something somewhere. I can find no info at all on the ST_TopologySummary() function. Not in the docs, & even Google cannot find a single reference. Where do I look for some explanation of this function (& any others that might be relevant )? Thanks, Brent --- On Thu, 4/5/12, Sandro Santilli <s...@keybit.net> wrote: From: Sandro Santilli <s...@keybit.net> Subject: Re: [postgis-users] Postgis topology help To: pcr...@pcreso.com, "PostGIS Users Discussion" <postgis-users@postgis.refractions.net> Date: Thursday, April 5, 2012, 5:49 AM On Wed, Apr 04, 2012 at 09:57:10AM -0700, pcr...@pcreso.com wrote: > Following on from the reply by strk (thanks!!) I'm still working through how > to use topologies. > > I have a script which creates a topology, adds 5 linestrings looking like: > > | | | > --------------- > | | | > --------------- > | | | > > validates the result and then Polygonizes it, creating two faces. Like this ? | | | -+------+------+- | | | -+------+------+- | | | > I'm using the SVN docs > ( http://www.postgis.org/documentation/manual-svn/Topology.html ) > as my reference, as this is the best I have found so far. > > What I want this script to do is run a query listing/describing the faces > that have been created, then extract them as polygon geometries into a > Postgis geometry column to be used as conventional polygons, but I can see no > way in the docs of accomplishing this. ST_TopologySummary gives you a good summary. You can use GetFaceGeometry to extract the faces polygons, maybe use it in a query to <yourtoponame>.face to see them all. Remember that face_id=0 is the universe face, so you want to skip that from the query. > Once I get the script able to complete this operation I figure I should have > a much better understanding of how Postgis topology works, & will stick it on > the wiki as a working example. I'll also insert more commands to illustrate > other operations, as I learn this stuff. > > Any suggestions as to how to accomplish these next steps? I think your next step should be looking at constructing TopoGeometry objects :) --strk; ,------o-. | __/ | Delivering high quality PostGIS 2.0 ! | / 2.0 | http://strk.keybit.net - http://vizzuality.com `-o------'
<<attachment: topo.png>>
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