This example uses a datastore location query to convert a VM (located on a vCenter Server) to OVF format.
> ovftool vi://username:pass@my_vc_server/my_datacenter?ds=[Storage1] foo/foo.vmx c:\ovfs\
or
> ovftool vi://username:pass@my_host/my_datacenter/vm/my_vm_folder/my_vm_name /ovfs/my_vapp.ovf