A quickie function that should hopefully print the dimensions of a node.

printBoundingSphere.lua

printBoundingSphere = function(node)
	local bs = node:getBound()
	print("Radius:", bs:radius())
	print("Center:", bs:center())
end

printBounds.lua

printBounds = function(node)
	local cbv = osg.ComputeBoundsVisitor()
	node:accept(cbv)
	local bb = cbv:getBoundingBox()
	local dims = {}
	for _, dim in ipairs{"x", "y", "z"} do
		dims[dim] = bb[dim .. "Max"](bb) - bb[dim .. "Min"](bb)
		print(dim, dims[dim])
	end
	return dims
end