Hi Sandro, I tried to run the two commands that you suggested. However, it returns some empty layers only. (e.g. test.edge, test.face...). I check that there are some warning message in the output pane.
I wonder if it is due to some geometry problem in the data set so that it cannot generate the topology. Besides, I am thinking to use ST_SNAP to clear some gaps between polygons. I have done some small test, it works. However, to apply the same for a layer containing hundreds polygons, it requires to loop through all the possible adjacent polygons respecting to each polygon. It will take a very very long processing time. Any other idea? Any method to filtering those gaps first? Meanwhile, it seems ST_CreateTopoGeo is doing similar things as you describe in the proposed toTopoGeometry. Correct me if I am wrong. It seems the toTopoGeometry performance should be better than the ST command, right? elton --- On Mon, 10/31/11, Sandro Santilli <[email protected]> wrote: > From: Sandro Santilli <[email protected]> > Subject: Re: [postgis-users] Build topology for polygon layer using postgis2.0 > To: [email protected], "PostGIS Users Discussion" > <[email protected]> > Date: Monday, October 31, 2011, 2:50 PM > On Sun, Oct 30, 2011 at 10:37:31PM > -0700, Elton Chan wrote: > > Hi there, > > > > I would like to build topology for a polygon layer > using postgis 2.0. The polygon layer contains contiguous > polygons snap to each another but some are having some > geometry error such as gap is found between polygons. > > > > Does anybody know the procedure to build topology with > abovemention polygon data? More precisely, any procedure to > convert all the polygons to line strings, then remove > duplicate lines, and build topology and remove > > small polygons. > > SELECT topology.CreateTopology('test', 4326); > SELECT topology.ST_CreateTopoGeo(ST_Collect(the_geom)) from > mylayer; > > Let it go while trick & treating as it'll take a > lot... > > A more scalable solution (the above does most work in > memory) and one > which would also create the TopoGeometry objects for you to > re-construct > the original point set in a value to use in your table, is > the toTopoGeometry > function which takes a GEOMETRY and put it into a topology > giving you back > the topologically-defined version of your GEOMETRY. Such > function is yet > to be done but is planned: http://trac.osgeo.org/postgis/ticket/1017 > and it is looking for co-funders (let me know if you're > interested). > > --strk; > > () Free GIS & Flash > consultant/developer > /\ http://strk.keybit.net/services.html > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
