Computing latitude longitude center point of a Polygon in PHP

I have a开发者_StackOverflow set of points (stored as lat/lon) for a polygon, I want to compute the lat/lon center point of the polygon in PHP.

Basically to do the same thing as the getCenter() function in Google Maps LatLngBounds.

Any ideas on how I can achieve this?

What you are looking for is the centroid of the polygon - which is pretty easy to compute. If you are using latitude/longitude the matter is complicated by the fact the the polygon is actually on the surface of a sphere (ellipsoid).

As an aside, why not just look at the Google api javascript code?

You can simply find a lot of formulas with the google queries "center of gravity polygon" or "polygon centroid"

The sample from Wikipedia: http://en.wikipedia.org/wiki/Centroid