  In this paper, we analyze the observability of the visual-inertial odometry
(VIO) using stereo cameras with a velocity-control based kinematic motion
model. Previous work shows that in general case the global position and yaw are
unobservable in VIO system, additionally the roll and pitch become also
unobservable if there is no rotation. We prove that by integrating a planar
motion constraint roll and pitch become observable. We also show that the
parameters of the motion model are observable.
