使用geokit或其他红宝石宝石来计算一系列地理坐标的中心

I've been using the geokit and geokit-rails gem for rails for awhile but one question I haven't found answered is how to find the calculated aggregate center for a collection of points. I know how to calculate the distance between two points, but not more than 2.I've been using the geokit and geokit-rails gem