[postgis-users] distance between two POINTM

[Michael Welter]

Hello,

I'm trying to calculate the distance between two POINTM.  The points are 
as received from a Garmin GPS and include the elevation of 2500m (I'm in 
the mountains).

The GPS receiver reported 5.2km between the two points, while 
distance_sphere() reported 4.5km.

What is the proper method to calculate distance on the earth's surface?

Thanks,