“…Let d ⊥ be a unit vector orthogonal to the plane defined by the three landmarks. Then, is observable on [ t 0 , t f ], t 0 < t f , in the sense that any initial condition is uniquely determined by the corresponding response { y ( t ), t ∈[ t 0 , t f ]} and system input { u ( t ), t ∈ [ t 0 , t f ]}, if the set of functions is linearly independent on [ t 0 , t f ]. Proof The proof is essentially a combination of the technical contents of the proof for single range measurements, detailed in , and the proof for the LBL configuration. It is presented in .…”