Sandro I am definitely going to read up something on PostGIS Topology, as it sounds really interesting. Thanks for your advice!
On 10/10/12, Sandro Santilli <s...@keybit.net> wrote: > On Wed, Oct 10, 2012 at 11:44:54AM +0200, Michal Zimmermann wrote: >> Thanks for the answers guys! I guess the data is ok, I was given them >> at the university which had bought it from the GIS company, that's why >> I trust this data source. Also when I try selecting the disctricts >> with ArcMap, it works (not with QGIS, though!). >> Sandro, would you be so kind and share some thoughts on PostGIS >> Topology? As I understood, it is a completely new feature of v2, >> right? What are the benefits? > > One benefit is making the spatial relationships explicit, so that > you could encode your counties as being composed by the districts, > and the districts would be composed by faces, which would be defined > by (shared) edges. > At that point querying for "all districts in a county" would just be > a matter of listing the components of a "county" TopoGeometry. > > But I guess you're still in the data preparation phase as you still > don't know which district record belong to which county, right ? > In that case you'll need ST_Covers (assuming the input data is > _really_ correct and doesn't contain cases in which the shape > of a district is slightly outside the shape of its county. > > Note that storing the data in a topology would be an excellent way to > have better control on those kind of data problems (often not easily > detectable as invisible to the eye). > > --strk; > > ,------o-. > | __/ | Delivering high quality PostGIS 2.0 ! > | / 2.0 | http://strk.keybit.net > `-o------' > > >> On 10/10/12, Sandro Santilli <s...@keybit.net> wrote: >> > On Wed, Oct 10, 2012 at 10:27:42AM +0200, Michal Zimmermann wrote: >> >> Hi to all, >> >> I have a relation representing all the counties in my country and the >> >> other one containing all the districts - e. g. each and every county >> >> is composed of several districts. How do I select them with spatial >> >> query? I tried with >> >> select nazorp from kraje as k, orp_wgs as o WHERE >> >> ST_Within(o.geom,k.geom) >> >> AND >> >> k.nazev = 'Liberecký' // name of the county >> >> >> >> but had wrong results returned (well, they are probably not wrong, >> >> they are just not what I expected them to be). ST_Within only returns >> >> districts that don't share a boundary with the county, but I need to >> >> get all the districts within the county. Is that possible? I haven't >> >> found any built-in function suitable for my needs yet. >> > >> > Try ST_Covers, which includes the boundaries. >> > >> > PS: yours is the perfect use case for PostGIS Topology ! >> > >> > --strk; > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users > -- Michal Zimmermann (zimmi) WWW: http://www.zimmi.cz _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
