code: def merge_vertices(self):
          
          # run unique rows
          unique, inverse = grouping.unique_rows(self.vertices)
  
          # apply unique mask to vertices
          self.vertices = self.vertices[unique]
  
          # apply unique mask to colors
          if (self.colors is not None and
                  len(self.colors) == len(inverse)):
              self.colors = self.colors[unique]
docs: Merge vertices closer than tol.merge (default: 1e-8)