A determination method of determining optimal routes for navigating naval vehicles by analysis of historical GNSS data; wherein the historical GNSS data comprise spatio-temporal historical trajectories made of sequenced of points, each defined by a position x, a position y and a time value t; each optimal route includes a sequence of waypoints; the determination method comprises the steps of: reducing the historical GNSS data transforming each historical trajectory into a corresponding reduced trajectory, eliminating all the points of the historical trajectory that do not determine changes of speed and/or course, i.e. retaining only the points of the historical trajectory that determine changes of speed and/or course; evaluating the similarity among reduced trajectories, thereby determining for each reduced trajectory a degree of similarity to all the other reduced trajectories; applying a first clustering algorithm that, based on the similarity among reduced trajectories, forms one or more clusters of reduced trajectories assigning to each cluster all and only those reduced trajectories that are similar among them; extracting the most representative reduced trajectory from each cluster formed by applying the first clustering algorithm; and identifying the optimal routes as the most representative reduced trajectories; the determination method is characterized in that: a. each most representative reduced trajectory of a cluster is used to initialise a second clustering algorithm that is applied to all the points of all the reduced trajectories belonging to said cluster to create groups of points around the points of the most representative trajectory; b. the groups of points are filtered to obtain waypoints clouds, each corresponding to a group of points obtained after having removed the points of that group that overlap to other groups, so to obtain groups of points that are non-overlapping among them around each point of the most representative trajectory; c. into each waypoint cloud, the time values t associated to each point are analysed to create time boundaries for each waypoint; d. the waypoints of each optimal route consist of the points of the corresponding most representative trajectory and of the corresponding waypoint clouds. reducing the historical GNSS data transforming each historical trajectory into a corresponding reduced trajectory, eliminating all the points of the historical trajectory that do not determine changes of speed and/or course, i.e. retaining only the points of the historical trajectory that determine changes of speed and/or course; evaluating the similarity among reduced trajectories, thereby determining for each reduced trajectory a degree of similarity to all the other reduced trajectories; applying a first clustering algorithm that, based on the similarity among reduced trajectories, forms one or more clusters of reduced trajectories assigning to each cluster all and only those reduced trajectories that are similar among them; extracting the most representative reduced trajectory from each cluster formed by applying the first clustering algorithm; and identifying the optimal routes as the most representative reduced trajectories; the determination method is characterized in that: a. each most representative reduced trajectory of a cluster is used to initialise a second clustering algorithm that is applied to all the points of all the reduced trajectories belonging to said cluster to create groups of points around the points of the most representative trajectory; b. the groups of points are filtered to obtain waypoints clouds, each corresponding to a group of points obtained after having removed the points of that group that overlap to other groups, so to obtain groups of points that are non-overlapping among them around each point of the most representative trajectory; c. into each waypoint cloud, the time values t associated to each point are analysed to create time boundaries for each waypoint; d. the waypoints of each optimal route consist of the points of the corresponding most representative trajectory and of the corresponding waypoint clouds. a. each most representative reduced trajectory of a cluster is used to initialise a second clustering algorithm that is applied to all the points of all the reduced trajectories belonging to said cluster to create groups of points around the points of the most representative trajectory; b. the groups of points are filtered to obtain waypoints clouds, each corresponding to a group of points obtained after having removed the points of that group that overlap to other groups, so to obtain groups of points that are non-overlapping among them around each point of the most representative trajectory; c. into each waypoint cloud, the time values t associated to each point are analysed to create time boundaries for each waypoint; d. the waypoints of each optimal route consist of the points of the corresponding most representative trajectory and of the corresponding waypoint clouds.