Forgot to CC: the list on my response...
---------- Forwarded message ---------- From: Matthew Perry <[EMAIL PROTECTED]> Date: Jan 14, 2008 2:14 PM Subject: Re: [Qgis-user] Points vs. Polygons To: Beowulf <[EMAIL PROTECTED]> Sounds like you'd be interested in a topological data model which would all you to store nodes and the connections/relationships between them (polygons). Postgis has pre-alpha support for this : http://postgis.refractions.net/support/wiki/index.php?PostgisTopology GRASS has a well established topological vector data model but I can't say if it would work well for your purposes. Another option would be to create your own psuedo-topological system and have a "nodes" table (your standard points table), a "polygon" table (with all non-spatial info about your parcels) and a "polygon_nodes_join" table which would join the two ...: polygon id | order | nodeid 1 | 1 | 101 1 | 2 | 102 1 | 3 | 103 1 | 4 | 101 Then have a query, script or stored procedure to generate a spatial polygon layer from the tables. - matt On Jan 14, 2008 1:58 PM, Beowulf <[EMAIL PROTECTED]> wrote: > > As you all know, PostGIS is a great way to store spatial data :) But here's > another question. > Let's say we have a PostGIS table that stores polygons. These polygons are > actually land plots, and there is a bunch of fields in that table to store > owner information, etc. The spatial data is stored as WKB in a BLOB. But > what if I want those polygon vertices to have some extra attributes to them? > Our cadastre expects us to name every point we've measured. > > A line in cadastral exchange file would look like this: > N=1,NP="132",X=5642997.41,Y=3340518.97,MX=0.05,MY=0.05 > > Meaning this is the first vertex in a polygon, it's name is "123", its > coords are 5642997.41 and 3340518.97. Also the error of measurement is 0.05 > meters for both X and Y. > > I suspect there is no way to attach that info to every vertex in a polygon. > But then maybe another table with spatial POINTs can be created? That way > every vertex may have all of its attributes defined. However, another > problems arises - how to link these points into a polygon. I feel that > having a polygon in another table that just repeats those points is a bad > idea because that info is redundant and it's going to be a pain in the butt > to make it coherent. > > Sure, I could ignore all that trouble and simply hardcode an error of 0.05m > in every measurement (since it doesn't change) and generate random point > names (since our cadastral system seems to ignore them anyway) but that just > doesn't feel right. Any ideas? > -- > View this message in context: > http://www.nabble.com/Quantum-GIS-and-cadastre-tp14477338p14815883.html > Sent from the qgis-user mailing list archive at Nabble.com. > > _______________________________________________ > Qgis-user mailing list > Qgis-user@lists.qgis.org > http://lists.qgis.org/cgi-bin/mailman/listinfo/qgis-user > -- Matthew T. Perry http://www.perrygeo.net "I love deadlines. I like the whooshing sound they make as they fly by." -- Douglas Adams _______________________________________________ Qgis-user mailing list Qgis-user@lists.qgis.org http://lists.qgis.org/cgi-bin/mailman/listinfo/qgis-user
