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Zhu et al. Intell Robot 2022;2(3):200­222  I http://dx.doi.org/10.20517/ir.2022.13  Page 208
























                       Figure 5. The 2D model of the bio-inspired neural network-based path planning algorithm. S, start; D, destination.


               Table 2 Algorithms for UUV point-to-point path planning
                  Algorithms          Logic                          Benefits          Drawbacks
                                      Visibility graph-based:
                                      (1) Establish as graph on the connection of the  Visibility graph-based:
                                      vehicle, polygonal obstacle vertex, and the      (1) Long time consumption
                                      destination without crossing the obstacles       when establishing the graph
                                      (2) Find the optimal path between the origin  (1) Easy to implement  (2) Lack of flexibility
                                      point and the destination point that has the     (3) Do not work for circular
                  Map Building                                       (2) Direct because of
                  Method  [33–40]     shortest distance              visible mapping   obstacles
                                      Grid-based:                                      Grid-based:
                                      (1) Decompose the surrounding area into          (1) Large computation
                                      nonoverlapping but connected cells               (2) Lack of consideration of
                                      (2) Address the optimal path between the origin  environmental disturbance
                                      and the destination cells without collisions
                                      (1) Predefine a virtual artificial potential field
                                      (2) Assume the destination provides the  (1) Simple mechanism  (1) Local minimum
                                      attractive force while obstacles generate
                  Artificial Potential                               (2) High efficiency and  (2) Sometimes induce large
                  Field  [41–47]      repulsive force to the vehicle  realtime reaction  computation
                                      (3) Address the optimal path for the vehicle
                                      through the field descending route
                                      (1) Regard the path planning as a search
                   Intelligent Path Planning  optimization problem                     (1) Unsatisfactory real-time
                    Algorithms  [48–52,55–64]  (2) Take the searching cost as the objective  (1) Easy to implement  reaction owing to the
                    (GA, ACO, Fuzzy logic,  function                 (2) Adaptiveness.  computation complexity
                       NN, and RL)                                                     (2) Local minimum
                                      (3) Optimization through iterations


               methods applied to the point-to-point path planning of a UUV can be found in the fourth part of Section 2.2.1.


               2.2.2. Full-coverage path planning
               The full-coverage path planning has to be considered when the vehicle reaches the designated search area,
               where the global area of the searching map shall be covered. The goal of the full-coverage path planning for
               the UUV is to simultaneously realize the high coverage rate, the low repetition route, and the short navigating
               distance.


               Therandomcoveragestrategywasproposedatearlytimestocompletethefull-coveragepathplanning. Maxim
               proposed a full-coverage path planning algorithm for multi-robots in the unknown environment, which does
               not need to obtain the global map information in advance, and the vehicles would not produce collisions with
               each other [65] . However, the random coverage strategy is used in this algorithm to traverse the operating area
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