  In this paper, we address the distributed pose estimation problem for
multi-agent systems, where the agents have unknown static positions and
time-varying orientations. The interaction graph is assumed to be directed and
acyclic with two leaders that have access to their position and orientation. We
propose a nonlinear distributed pose estimation scheme relying on individual
angular velocity measurements and local relative (time-varying) bearing
measurements. The proposed estimation scheme consists of two cascaded
distributed observers, an almost globally asymptotically stable (AGAS) attitude
observer and an input-to-state stable (ISS) position observer, leading to an
overall AGAS distributed localization scheme. Numerical simulation results are
presented to illustrate the performance of our proposed distributed pose
estimation scheme.
