“…To account for maneuvering targets, all the PN results originated from two-dimensional space and the PN-variant guidance algorithms can be augmented to the case of maneuvering targets with known exact acceleration, including the true proportional navigation (TPN), 1,3,4 the realistic true proportional navigation (RTPN), [5][6][7] the ideal proportional navigation (IPN), 8,17 the general true proportional navigation (GTPN), 3,9,23 the general ideal proportional navigation (GIPN), 23 the pure proportional navigation (PPN), 2,17,19,24 the augmented proportional (APN), 10,11,[13][14][15] the augmented pure proportional navigation (APPN), 16 and the optimal guidance laws (OGL). [25][26][27][28] Unfortunately, the target information is usually hard to be measured or estimated as the target maneuvers change rapidly, and the complexity and the cost of the guidance system may be increased as more sensors and estimators are required.…”