FIND CENTRE OF COLLECTION OF POINTS

Hi, 

I have a point cloud which I have exported to CSV from rhino and then imported back in through grasshopper. 

There are approx 50,000 points, and I need to find the centre point. 

The way I thought of doing it, was to copy all the points and give the copies a Z value of Z=0. Then create a flat surface from these and use the Polgyon Centres tool to do this, but I can't even produce a flat surface from these. 

Any help would be really appreciated...?? 

Thanks, 

Josh