On Sun, Apr 01, 2012 at 12:26:27AM -0700, pcr...@pcreso.com wrote: > 1. depth contours > 2. arbitrary lines between contours (generally following a lat or long) > 3. areas of land or other excluded areas which are excluded from any strata > overlapping them. > > My current Postgis model defines strata outer boundaries as polygons, > holes as polygons, & instantiates strata as a set of one or more outer > boundaries less any holes. > > This has the usual issues of slivers & overlaps between strata as > common boundaries are stored twice, & as not always identical. > > If I used topologies, I could store the constituent lines (contours, > etc) and assemble the outer boundaries from these, to give properly > normalised polygons.
Yes you could > I have seen the docs & Strk's presentation, but these to not (to me > anyway) list the steps to follow to do something like this, & the Postgis > functions to carry out those steps. That's because toTopoGeom wasn't yet implemented when I made the presentations :) I'd need to update those. The simplest way for you to start would be load all your data into a topology. The toTopoGeom function should (theoretically) take care of finding duplicates and reusing existing portions of your lines and nodes. Of course if you have slivers & overlaps your resulting topology would still have additional faces you'll want to drop or gaps you'll want to fill. If you're sure about (1) and (2) you could also only add those using toTopoGeom and then construct (3) "manually" (by defining TopoGeometry objects using the CreateTopoGeom function. In sql-mm language your "outer boundaries less any holes" would be "outer face plus inner faces", ie: +-----------+ A + B + C == the whole surface you see, with no holes | A | | +---+ | | | B | +-+ | | +---+ |C| | | +-+ | +-----------+ You may notice there are not functions to add or remove elements (B,C) from TopoGeometry objects. That would be a nice addition for easier editing of a TopoGeometry composition after creation. --strk; ,------o-. | __/ | Delivering high quality PostGIS 2.0 ! | / 2.0 | http://strk.keybit.net - http://vizzuality.com `-o------' _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
