I dont remember the exact procedure, but in the Hierarchy of all of the objects you can set their pivot point. Just select an object go to it's heirarchy, and look for the pivot section. There are buttons for different purposes, one will set it to the center of the object, i believe another will set it to be the middle of the world.
Alternatively, if you take your 3d pillar, move it out to the distance you want, export it, and then import it again, the pillar's pivot point should be the middle of the 3D world. You could then rotate this pillar a bunch of times to get the complete circle.