Method to locate nearest lng/lat locations without a 15 mile radius?

问题

Project: I have a MySQL database of alumni home address locations stored as lng/lat. I want to be able to identify groups of 15 members or more of alumni that live within a 15 mile radius of each other.

Given a lng/lat, how do I select the other lng/lat locations that are within a 15 mile radius? I've installed on Linux the PHP geonames package from PEAR. It isn't clear to me if I can use this package for aid in this function. It contains radius routines, but they appear to be for returning information such as postal codes within a lng/lat radius. Thanks!

回答1:

You'll need to look into using the Haversine Formula. You'll find plenty of online examples showing you how to implement the formula in both PHP and SQL.

Google has a nice example for MySQL:

SELECT id, ( 3959 * acos( cos( radians(37) ) * cos( radians( lat ) ) * cos( radians( lng ) - radians(-122) ) + sin( radians(37) ) * sin( radians( lat ) ) ) ) AS distance 
FROM markers HAVING distance < 25 ORDER BY distance LIMIT 0 , 20;

回答2:

Wayne's answer is interesting, but I wonder whether over 15 miles the spherical component can be ignored, using trig instead? Pseudocode:

For every (x1, y1) row:
    Loop through every (x2, y2):
        Distance = SQRT ( ( x2 - x1 ) ^ 2 + ( y2 - y1 ) ^ 2 )
        If (Distance <= 15)
            // ...
        End If
    End
End

Or a SQL version (not sure I've got powers correct, but you get the idea):

SELECT
    SQRT ( ( a2.x - a1.x ) ^ 2 + ( a2.y - a1.y ) ^ 2 ) AS distance
FROM alumni a1, alumni a2
WHERE a1.id != a2.id
HAVING distance <= 15;

Thinking about it, the 15 miles will have to be converted from lat/long.

来源：https://stackoverflow.com/questions/12527541/method-to-locate-nearest-lng-lat-locations-without-a-15-mile-radius

标签

php

mysql

latitude-longitude