# Navigation of Autonomous Tug via Evolutionary Algorithms with Radar Plot Fitness Evaluation
## 5 Discussion  
The conducted research has shown that the use of an evolutionary algorithm with a radar-based fitness assessment method allows for the effective determination of safe routes for an autonomous tugboat in restricted waters and in situations similar to those encountered in ports and their roadsteads. Compared to the classic evolutionary algorithm, the solutions proposed by the radar-based algorithm for assessing the degree of adaptation are characterized by:  
* Fewer route turn points--in situations 1, 2 and 4, the radar-based algorithm generated routes 1-2 turn points shorter than the classic method,
* Reduction in the total course change--particularly visible in situations 1 (24.7%) and 3 (53.6%), which translates into lower energy consumption,
* Maintaining safer distances from static obstacles--the routes generated by the radar algorithm consistently bypassed islands with a greater safety margin,
* Comparable or slightly shorter total route length--differences in route lengths ranged from \(-0.8\%\) to \(+0.97\%\). The proposed evolutionary algorithm with an innovative method of fitness determination using a radar plot is intended for use in controlling autonomous marine vehicles, as well as entire formations of such vehicles, while other methods described in the literature so far are usually intended only to support decision-making by navigators of the ship It should be emphasized that the presented algorithm makes decisions taking into account both static and dynamic constraints, unlike many algorithms described in the literature, focusing mainly on the movement of other ships, entirely omitting static constraints. The innovation of the proposed algorithm is manifested in the possibility of quickly changing the set of criteria for assessing fitness, by replacing a set of one radar plot coefficients with another, or by adding new radar plot coefficients, depending on the change in the nature of the navigation situation. It is worth noting that the radar-based algorithm demonstrated particular effectiveness in highly complex situations (situation 4), where, despite a greater number of navigation constraints, it was able to determine a safer route with a similar total length. The solutions generated by the proposed algorithm have parameters similar to the solutions proposed in a given situation by professional navigators. When applying the described algorithm in a real ship, it would be necessary to take into account the situation when one of the other ships changes the parameters of its movement. The most effective tool for identifying such a situation is the AIS system, where information about the course and speed is sent by the ship in an open form, which allows for a quick determination that a significant change in its movement has occurred. The ARPA (Automatic Radar Plotting Aids) attachment to the navigation radar is an another device that allows obtaining data on the course and speed of moving objects in the environment, and therefore also on their significant changes. In such a case, the calculations can be repeated, taking into account the new parameters of the other ships' motion and the new starting position. An improvement in the case of recalculation could be introduction of another criterion for fitness assessment, taking into account maintaining the initial course and speed of the own ship for a certain period of time. This would allow maintaining a predictable course of movement and would limit maneuvering to the minimum necessary to react to the change in the situation. This approach is consistent with the ideas processed in the IMO within the e-navigation initiative [41] and related proposals for the real-time communication system VHF Data Exchange System (VDES).