distance queries by coordinates in rails 3.x

Question

I have a location object with latitude and longitude attributes and I want to query the database for objects within a specific distance from a current latitude / longitude location.

I read about the 'geocoder' gem which seems to be able to do what I'm looking for, but in order to add the obj.near functionality I need to add geocoding to the object. I don't need geocoding or reverse geocoding at all, just distance queries by coordinates.

can I add the .near functionality to an object with 'geocoder' without adding any geocoding functionality ? is there another or a better way to do what I want ?

Answer 1

Why don't you look at the geocoder source? It's on github. I think the class you are looking for is stores/active_record.rb

Obviously you won't be getting the extensibility or other benefits of using a library but this will give you the code you need.

Edit: This will give you a UDF in mysql that will calculate the distance

DROP FUNCTION IF EXISTS calculateDistance; 
delimiter |
CREATE FUNCTION calculateDistance (originLatitude FLOAT, originLongitude FLOAT, targetLatitude FLOAT, targetLongitude FLOAT) 
returns FLOAT
deterministic
BEGIN
DECLARE radianConversion FLOAT;
DECLARE interim FLOAT;
DECLARE earthRadius FLOAT;

SET radianConversion = 180 / pi() ;/*57.2957795130823;*/
SET interim = SIN(originLatitude/radianConversion) * SIN(targetLatitude/radianConversion) + COS(originLatitude/radianConversion) * COS(targetLatitude/radianConversion) * COS(targetLongitude/radianConversion - originLongitude/radianConversion);

IF interim > 1 THEN
    SET interim = 1;
ELSEIF interim < -1 THEN
    SET interim = -1;
END IF;
SET earthRadius = 6371.0072;
RETURN earthRadius * ACOS(interim);
END|
delimiter ;

select calculateDistance(43.6667,-79.4167,45.5000,-73.5833);

Then you just need to pass the correct values from a method on your class to get this to fire off. Obviously this won't work on Sqlite

Answer 2

There is a RailsCast about Geocoder, from what I've seen you need to add latitude and longitude to your model and gecoder will work.