TABLE I.

Observation of the state variables

Variables	Definition
r	$\overline{PQ}∕2=\sqrt{{(x_Q^W-D_x)}^2+{(D_y-y_P^W)}^2}∕2$
$x_P^B$	$\sqrt{4r^2-{\left(y_Q^B\right)}^2}$
α	$ta{n}^{-1}(y_Q^B∕x_P^B)$
θ	$ta{n}^{-1}((D_y-y_P^W)∕(x_Q^W-D_x))-\alpha$
${\mathbf{O}}^W={[x_O^W,y_O^W,0]}^T$	${[D_x+x_P^{B}cos\theta ,y_P^W+x_P^{B}sin\theta ,0]}^T$