PHP / MySQL - Find all items in 500 meters radius from actual gps coordinates

Question

I'm doing some compare of prices in same location based on GPS coordinates. So eg I've got an item with coordinates:

lat: 45.815005 
lng: 15.978501

I want to search in my MySQL database for each items which are eg 500 meters around that place. (it doesn't need to be circle, just 500 meters on X and 500 meters on Y both ways). Lat and lng are stored as a separate columns type float(10,6) in my DB

I am aware of the fact it's not easy to calculate exact lng and lat but I'm fine if I miss few meters each site.

This is pretty complex question but I would be thankful for any advise which will kickoff my start.

Answer 1

Calculating the distance between two coordinates isn't actually that difficult given the haversine formula.

SELECT 
  -- stuff here
  , ( 6371000 * acos( cos( radians(45.815005) ) * cos( radians( stuff.lat ) ) * cos( radians( stuff.lng ) - radians(15.978501) ) + sin( radians(45.815005) ) * sin(radians(stuff.lat)) ) ) AS distance 
FROM 
  stuff
HAVING 
  distance < 500

Referenced Answer

Necessary changes from the original answer:

1. The constant offered in the original answer supplied the values for miles or kilometers. I've changed the constant here to work with meters.

2. The constants have changed to use your coordinates. You might want to adapt the query a little further to make those parameters instead of constants.

3. The having expression changed a little to reflect your desire for 500 meters. Again, this might be something you want to parameterize.