OK, I feel like I've got a fundamental block about how spatial data is actually used in the real world and how spatially aware databases actually make use of that data. This is probably quite obvious for everyone so please bear with me.
I've been playing with a bunch of spatial databases (Oracle, Postgis, DB2) and from what I can tell, all tend to roughly follow the OGC SFA spec (Oracle using different terminology). Now it also seems that the SFA spec deals EXCLUSIVELY with Cartesian coordinates. Now here's my first confusion. If they only deal with Cartesian coordinates, why do they allow you to specify SRIDs that are lat/long based. Will any of the SFA functions work with lat/long (other than ST_Transform(), which is actually a SQL/MM and not even included in SFA)?? My next area of confusion is that I've looked at a bunch of data from people such as Navteq, teleatlas, and a bunch of individual companies databases, and it seems that every single one ships and stores their data in lat/long. So what the heck? If the tools can't deal with lat/long, why does everyone ship and store their data in lat/long? Does everyone project this data before actually loading it into the db? Help!? Now, it appears that Oracle in particular can do some functions with lat/long directly (the distance calculation comes to mind), and I know Postgis has some specialized distance functions for geodetic coordinates, but I'm not sure if that extends to the whole function set (i.e. can I do an Intersection of two polygons specified in lat/long coordinates??). Why doesn't the OGC SFA spec and libraries support all the functions with geodetic coordinates directly rather than require projected coordinates? Finally, how do the analysis and visualization tools that people put on top of these databases deal with these questions? (e.g. MapInfo, ArcView, etc.) They seem to want lat/long data as well, but if you stored project coordinates in the database isn't there a problem?? HELP! -Rick _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
