Haversine vs Equirectangular approximation

Question

So, I need to calculate distances betweeen two points (lat-lon pairs). I've read about Haversine formula and Equirectangular approximation in Movable Type Scripts.

Since I only want to calculate short distances (less than 4 KM), is the Equirectangular formula a good approximation?

Also, I've read about lat-lon storage in MySQL databases in Google Developers documentation and they implement the Haversine formula like this:

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;

My last question is, is there any big performance differences between filtering the points in the sql query (as in the example) and filtering them by code?.

Answer 1

When I tested haversine v equirectangular over much larger distances (1000km, within the UK), the difference was on the order of 0.1%. So for distances of 4km or less you might as well use equirectangular for speed unless you have a need for maximum accuracy.