Geolocation and Haversine formula

Question

I am trying to create a basic web application that detects the users geolocation, queries a mySQL database, and returns all bus stops within say 5 kilometers.

The GTFS feed including the Longitude and Latitude have been inserted into a mySQL database, and I found a example HTML page that provides the Longitude and Latitude of the browser accessing the web application.

I am seeking some help writing the mySQL query that takes this information and returns the results.

Answer 1

In this link you find:

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;

Answer 2

Although the great circle formula is precise, you don't need the precision in this case. A minute of latitude is about 1 mile (1.6 km). A minute of longitude is about cos(LAT)*1 mile. I would consider selecting for the box of LAT +/- 3 minutes, and LONG +/- (3/cos(LAT)) minutes. If you really need a circle, not a box, then just pretend it's Euclidean coordinates. The error on this scale is less than the length of the bus.

The only tricky part is that the length of a minute of longitude varies depending on how far from the equator you are.