Triangulate/find the center of 3 x 3d points in After Effects?

I think this works:

p1 = thisComp.layer("3D Layer 1").transform.position;
p2 = thisComp.layer("3D Layer 2").transform.position;
p3 = thisComp.layer("3D Layer 3").transform.position;
(p1 + p2 + p3)/3


Dan