  This letter presents two bearing-constrained formation tracking control
protocols for multiple nonholonomic agents based respectively on the bearing
vectors and displacements between the agents. The desired formation pattern of
the system is specified by the desired inter-agent bearing vectors. In the
proposed control schemes, there are two or more leaders moving with the same
constant velocity; the other follower agents do not have the information of the
leaders' velocity nor communicate variables with their neighbors. Under both
the proposed control laws, the system achieves the moving target formation
asymptotically. Simulation results are provided to support the theoretical
development.
