  Relative pose estimation between fixed-wing unmanned aerial vehicles (UAVs)
is treated using a stable and robust estimation scheme. The motivating
application of this scheme is that of "handoff" of an object being tracked from
one fixed-wing UAV to another in a team of UAVs, using onboard sensors in a
GPS-denied environment. This estimation scheme uses optical measurements from
cameras onboard a vehicle, to estimate both the relative pose and relative
velocities of another vehicle or target object. It is obtained by applying the
Lagrange-d'Alembert principle to a Lagrangian constructed from measurement
residuals using only the optical measurements. This nonlinear pose estimation
scheme is discretized for computer implementation using the discrete
Lagrange-d'Alembert principle, with a discrete-time linear filter for obtaining
relative velocity estimates from optical measurements. Computer simulations
depict the stability and robustness of this estimator to noisy measurements and
uncertainties in initial relative pose and velocities.
