“…As error is accumulated, the UAV's estimate of the position variance increases the uncertainty about its location. For a UAV in space, its position is described by the x, y, z coordinates and an angle, i.e., q n = [q x , q y , q z , θ] T n , where q x , q y , q z are positions on three axes and θ is the angle [108]. As shown in Equation ( 2), the change in position and angle between two timestamps is ∆q n = [∆q x , ∆q y , ∆q z , ∆θ] T n .…”