Question

I’m currently using this query to get a town inside my DB by giving a coordinate :

SELECT *
FROM citiesTable
WHERE latitude  >= ? AND latitude  <= ?
  AND longitude >= ? AND longitude <= ?;

This code works well and do I want but sometimes the query doesn’t match anything…
So, in this case, I would put a bird distance to this query in order to get adjacent town.
Any suggestion on how can I do that ?

Answer 1

Searching for “distance from longitude and latitude” gave a link to http://www.movable-type.co.uk/scripts/latlong.html which specifies this code for calculating the distance:

var R = 6371; // km
var dLat = (lat2-lat1).toRad();
var dLon = (lon2-lon1).toRad();
var lat1 = lat1.toRad();
var lat2 = lat2.toRad();

var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
        Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2); 
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
var d = R * c;

A couple more minutes of searching led to http://www.movable-type.co.uk/scripts/latlong-db.html

That page is chock-full of information. Here’s a simple (but inefficient) solution, assuming your town is at $lon,$lat and $R is 6371 (which is km), and finally that you want the cities to be within $rad of your town:

Select ID, Postcode, Lat, Lon, 
       acos(sin($lat)*sin(radians(Lat)) + cos($lat)*cos(radians(Lat))*cos(radians(Lon)-$lon))*$R As D
From MyTable 
Where acos(sin($lat)*sin(radians(Lat)) + cos($lat)*cos(radians(Lat))*cos(radians(Lon)-$lon))*$R < $rad