In contrast to NSGA-II, the NSGA-III algorithm , uses reference directions 42,43 instead of a crowding distance to enforce diversity in the selection of solutions within the splitting front. Reference directions are determined by a predefined set of points on the unit simplex in fitness space. Each reference direction is defined as a ray originating from the origin and passing through exactly one of these points. NSGA-III assigns a reference direction to each solution in the population based on the nearest perpendicular distance (in normalised fitness space) to the corresponding direction. In the splitting front selection procedure, the NSGA-III algorithm prioritises reference directions that are underrepresented in the current surviving evolutionary population.