Radius Search: What's closest to me?

[fireproofsocks]

A variation on the Gmarker snippet:

Include a &radius parameter that will filter the viable resources specified by the other parameters (i.e. the &parents or &resources).

E.g.

&radius=`5`
&radius=`5mi`
&radius=`8km`

OR

&radius=5 &units=miles

Related: add a system setting specifying the unit (miles or kilometers).

Search for "Great Circle" calculations for some inspiration:

http://stackoverflow.com/questions/574691/mysql-great-circle-distance-haversine-formula
http://stackoverflow.com/questions/1727137/sql-query-for-performing-radius-search-based-on-latitude-longitude

Another solution for this problem is to use a square instead -- this makes it a bit easier on the maths involved because you simply use a greater-than / less-than comparison on the lat/lng coordinates.

This should also set a placeholder for "results_msg" or "no_results" where we can say "There are X results within Y miles of you!" or "There were no results".

A related search is "Find the closest to me" -- check out this braindump powerpoint!
http://www.scribd.com/doc/2569355/Geo-Distance-Search-with-MySQL

Also http://www.sphinxsearch.com/

Sample query:

CREATE PROCEDURE geodist (IN userid int, IN dist int)BEGINdeclare mylon double; declare mylat double;declare lon1 float; declare lon2 float;declare lat1 float; declare lat2 float;
-- get the original lon and lat for the userid 
select longitude, latitude into mylon, mylat from users5where id=userid limit 1;
-- calculate lon and lat for the rectangle:
set lon1 = mylon-dist/abs(cos(radians(mylat))*69);set lon2 = mylon+dist/abs(cos(radians(mylat))*69);set lat1 = mylat-(dist/69); set lat2 = mylat+(dist/69);
-- run the query:
SELECT destination.*,3956 * 2 * ASIN(SQRT( POWER(SIN((orig.lat -dest.lat) * pi()/180 / 2), 2) +COS(orig.lat * pi()/180) * COS(dest.lat * pi()/180) *POWER(SIN((orig.lon -dest.lon) * pi()/180 / 2), 2) )) asdistance FROM users destination, users originWHERE origin.id=userid
and destination.longitude between lon1 and lon2 and destination.latitude between lat1 and lat2 
having distance < dist ORDER BY Distance limit 10;END $$

Really, this would need to be a variation on the resourceQuery Snippets.