- From: Geoff Chappell <gchappell@intellidimension.com>
- Date: Sun, 16 Apr 2006 10:10:52 -0400
- To: "'Christopher Schmidt'" <crschmidt@crschmidt.net>, "'Luk Vloemans'" <luk.vloemans@student.uhasselt.be>
- Cc: <semantic-web@w3.org>
> -----Original Message----- > From: semantic-web-request@w3.org [mailto:semantic-web-request@w3.org] On > Behalf Of Christopher Schmidt > Sent: Sunday, April 16, 2006 8:53 AM > To: Luk Vloemans > Cc: semantic-web@w3.org > Subject: Re: SPARQL & SemWeb > >[...] > > In that case, what you would probably want to do is create a bounding > box wide enough to capture all your results, then do secondary > processing to determine the actual distance. So the process would be > something like: > > * Take '500m' input from user > * Turn 500m into a bounding box containing the area no matter where on > the globe it is -- this requires some extra query selection > * Select your data from the database > * Post-process the data by running a comparison on the actual > distances -- this is where you bring in curvature of the earth, etc. > into the equation. I did something like this with the TIGER/line census data a while back -- not sparql at the time, but RDF queries (which could easily be sparql now). See example #6 at: http://labs.intellidimension.com/tiger/ In that query, I use a custom rule to filter by radial distance after first selecting candidate points within a bounding box (I assumed world was flat because RDF Gateway lacked inverse trig functions at the time). In sparql, I suppose that custom rule could be an extension function. -Geoff
Received on Sunday, 16 April 2006 14:11:57 UTC