This sets the point to rotate and scale the object about, relative to its local coordinate system. The default center is [0,0,0].
import viz
import vizact
import vizshape
viz.go()
# Create object with offset center and spin around it
model = viz.add('beachball.osgb',pos=(0,0,10))
model.setCenter([1,0,1])
model.addAction(vizact.spin(0,1,0,45))
# Add sphere representing objects center
vizshape.addSphere(radius=0.1, pos=model.getCenter(), parent=model)