# An Approach to Multi-Objective Path Planning Optimization for Underwater Gliders
## 6 Conclusions and Future Work  
Overall, a useful methodology/tool was built and can be applied to multi-objective underwater glider path planning, obtaining a set of non-dominated solutions simultaneously minimizing the distance to target and maximizing the minimum distance to one or more obstacles. Multiple simulations were performed in the geographic region of Canary Islands, demonstrating the suitability of the methodology. Those tests included favourable, side, and against ocean currents, different obstacle locations and different start and target points, all of them possible situations that can occur during a glider mission. The system described here can now be easily configured and tuned to be used as a planning tool for glider pilots, to help determine, together with their expertise and knowledge, which are the best trajectories to pursue during a specific mission. Obviously, the results are conditioned by the quality of the ocean currents data and/or forecast, due to the uncertainty associated to forecasts. In any case, higher skill rank predictors are continuously proposed, with better spatial and temporal resolution characteristics. The proposed methodology was able to produce satisfactory trajectories using the genetic algorithm NSGA-II. It is worth mentioning that the optimizations include well spread solutions that go from one extreme to another. This means that solutions include results that, in this case, crossed the safety radius to obtain a better distance to target point (through a straight line) or move away from the safety radius, increasing safety at the expense of worse target distances. From the results obtained and discussed previously, it is possible to state that the described system, through the usage of the genetic based evolutionary algorithm NSGA-II, is able to produce usable paths, being the best ones obtained using configuration 16 (PS 100 NG 200 CP 1.0, and MP 0.15) for all simulated cases. The main contributions seek with this work were also achieved: NSGA-II can be used to optimize multi-objective glider path planning, an innovative and challenging engineering problem, never addressed this way. The best parameter combination was found for the designed scenarios (configuration 16), but the system can be adjusted to other locations, to benefit control teams, in need of valuable information for critical decision making situations, potentially extending the vehicle operational potential and thus increasing the mission productivity. Future works include considering aspects like battery consumption to accomplish the mission, areas of interest to intensify sampling or marine traffic that represent real obstacles to glider navigation. These aspects can be included as additional fitness functions with more parameters to be taken into account. Also, a comparison with other evolutionary algorithms could be done, to evaluate the complexity and performance of the described system against other optimization techniques, on a more extensive work. The usage of very high-resolution forecasts, with more outputs per day and additional oceanographic/atmospheric variables can also be an interesting possibility to consider, as the solutions are as accurate as the accuracy of the forecasts provided. With all these aspects to be considered on a future work, as they increase the computational costs, the optimizations will need to be executed on a computational cluster, in order to run even more optimizations simultaneously. Also, using a GPGPU (general-purpose graphics processing unit) could be a relevant improvement, due to their ability to do massive parallelism and speed up the optimization process. Progressively moving this infrastructure to standard platforms like ROS is also planned to ease sharing results, provided that authors are able to keep optimization times inside practical levels. As a final remark, it would be interesting to validate the results obtained with real glider missions; something complicated in this moment since it would require exclusive multi glider use for long periods.