Question

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Radius of multiple latitude/longitude points
distance calculations in mysql queries
select within 20 kilometers based on latitude/longitude

I have a MyISAM table, which the data is stored in. The data includes latitude and longitude for Google Maps. What I am trying to achieve is to select all objects within the radius of 40 kilometers of the sample latitude and longitude.

Thanks!

Answer 1

I use this query to get all points within a $radius around $lat/$lng:

SELECT
    *,
    ( 6371 * acos( cos( radians({$lat}) ) * cos( radians( `lat` ) ) * cos( radians( `lng` ) - radians({$lng}) ) + sin( radians({$lat}) ) * sin( radians( `lat` ) ) ) ) AS distance
FROM `positions`
HAVING distance <= {$radius}
ORDER BY distance ASC

6371 is the earth radius im km. And I have not invented it:
http://code.google.com/intl/en/apis/maps/articles/phpsqlsearch.html
https://developers.google.com/maps/articles/phpsqlsearch_v3#findnearsql (edit: URL changed)