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geocode radius search

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I'm trying to figure out the best way to do a radius search based on latitude and longitude.


What I'm doing that works: I'm loading each record key and lat/long into an array, geocoding the distance from a set point, then sorting the array by that distance. It's pretty heavy - but not bad for the 30 records I'm working with.


What's a better way to do this with hundreds or even thousands of records?

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The end goal is to get the distance of hundreds of different points in the same general geographic area from any random location in the same area on the fly. I'll want to dump the fifteen closest as points on an embedded map api. The distances will be recalculated on map move, and the 15 closest locations will replace the old 15.


I didn't want to muddy this discussion with code, since the code itself isn't the problem (since it works). The problem is I have to call this code for each location in the entire database to establish a distance from my arbitrary location before I can sort out fifteen of them.

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if your using mysql you can try...

$lat/$lon has to be the point from which you want to locate... 
$miles=10; or how many miles you want to radius... 
and just limit the result to 15.... 
SELECT ((ACOS(SIN($lat * PI() / 180) * SIN(lat * PI() / 180) + COS($lat * PI() / 180) * COS(lat * PI() / 180) * COS(($lon - lon) * PI() / 180)) * 180 / PI()) * 60 * 1.1515) AS distance FROM members HAVING distance<='$miles' ORDER BY distance ASC

(code I found on google)

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Very nice! Well, since we're in the math forum, I just have to ask what the difference between your code (which works wonderfully, by the way) and the following code is?



    SELECT `id`, X(gm_coor) AS `latitude`, Y(gm_coor) AS `longitude`,
          POW(COS(RADIANS($lat)) *
               SIN(RADIANS(Y(gm_coor) - $lon)), 2) + 
          POW(COS(RADIANS(X(gm_coor))) * SIN(RADIANS($lat)) - 
              SIN(RADIANS(X(gm_coor))) * COS(RADIANS($lat)) * 
              COS(RADIANS(Y(gm_coor) - $lon)), 2)), 
        (SIN(RADIANS(X(gm_coor))) * SIN(RADIANS($lat)) + 
         COS(RADIANS(X(gm_coor))) * COS(RADIANS($lat)) * 
         COS(RADIANS(Y(gm_coor) - $lon)))
      ) * 6372.795 AS `distance` 
    FROM `my_table`
    HAVING `distance` < 1

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