On Thursday 15 May 2008, Bruce Rindahl wrote: > Has anyone thought about the Arc/Info coverage model? The idea would be > to have a table with line geometries and attributes reflecting the left > and right polygon ids. My thought is you do your edits on the line > geometry table and then polygon topology is built in a separate > (dependent, inherited??) table based on the line table using well > defined procedures. The only function I don't see offhand that is not > there is a split polygon with line. Just my thoughts. > > Bruce Rindahl
Along these lines (so to speak) the GRASS model for encoding topology would be another candidate. Cheers, Dylan > > Webb Sprague wrote: > > On Thu, May 15, 2008 at 5:20 AM, George Silva <[EMAIL PROTECTED]> wrote: > >> Hello all again, > >> > >> I´m curious. I´ve said in qgis list and some other 'desktop' GIS > >> software lists that the biggest feature missing for OSGIS is something > >> like the 'auto-complete' polygon in ArcGIS,, that would make life much > >> easier. > > > > Indeed! > > > >> I´ve been reading some things, and i´ve seem people mentioning trigger > >> based topology (eg cut out the overlaping area of digitized polygons, > >> or,maintain only the overlaping areas of the digitized polygons, and > >> other related issues). > > > > I think the hard part is deciding how you want to do this exactly, > > since all approaches involve changing the data somehow; a lot of > > people are chary of automatically deleting gaps, for example, lest > > they aren't really gaps (consider the Vatican Republic in a map of > > euro nations...). > > > >> I imagine that would be a trigger using something like after insert > >> update the_geom. > >> > >> Can you guys with more experience give me a example, so i can build my > >> own? Best pratices? Some light around this subject? > > > > Have you ever written a non-geo trigger in postgresql? If not, I > > would practice using the docs; I am pretty sure you could just modify > > NEW with a geo operator/ function. > > > > If so, I think a larger scale project needs to be embarked on. The > > work so far seems to me to be quite low level without a grand plan, > > and I think a grand plan is needed. I would start with a bunch of > > functions for modifying a geometry based on its neighbors and some > > topology constraints, then maybe a schema to store topology > > information, and only then start implementing triggers. But this is > > armchair quarterbacking--hopefully someone with some real experience > > will say something... > > _______________________________________________ > > postgis-users mailing list > > [email protected] > > http://postgis.refractions.net/mailman/listinfo/postgis-users -- Dylan Beaudette Soil Resource Laboratory http://casoilresource.lawr.ucdavis.edu/ University of California at Davis 530.754.7341 _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
