Ship decoupling-fusing positioning algorithm based on velocity direction constraint

To improve the positioning precision of ship in ocean perturbing environment, a decoupling-fusing positioning algorithm (DFPA) is proposed based on velocity-direction constraint (VDC). Firstly, the strong tracking filter (STF) is combined with the VDC by utilizing Lagrange multipliers method to enhance the space relativity of the ship positioning. Then, to decrease the complexity of STF-VDC technology and to increase the positioning robustness, the fusing position is obtained from the decoupled three-dimensional velocity directions by Helmert variance estimation method. The results of Monte Carlo simulation show that compared with the conventional STF method on a typical sea-route which includes turns and straight line maneuvers, the proposed algorithm maintains the strong tracking constraint of velocity directions with a half of position precision of STF.