设计问题：如何确定多个纬度/长点之间的距离？

Question

Planning on developing a LAMP web application that allow users to specify their location. I could possibly use Google Map API to convert their location into lat/long coordinates. Assume each user has lat/long coordinates, how do I do the following:

• display the distance between 2 users?
• search for users within a given radius?

UPDATE: SOLUTION USING MySQL: MySQL Great Circle Distance (Haversine formula)

Answer 1

Here is a MySQL stored function I wrote only the other day to calculate Haversine distance:

In this question:

Why does this MySQL stored function give different results than to doing the calculation in the query?

Usage:

SELECT haversine(lat1,lng1,lat2,lng2,units);