docs: def is_triangular(self, var):
          """
          Test if a variable is on a triangular grid
  
          This method first checks the `grid_type` attribute of the variable (if
          existent) whether it is equal to ``"unstructered"``, then it checks
          whether the bounds are not two-dimensional.
  
          Parameters
          ----------
          var: xarray.Variable or xarray.DataArray
              The variable to check
  
          Returns
          -------
          bool
              True, if the grid is triangular, else False"""
          warn("The 'is_triangular' method is depreceated and will be removed "
               "soon! Use the 'is_unstructured' method!", DeprecationWarning,
               stacklevel=1)
          return str(var.attrs.get('grid_type')) == 'unstructured' or \
              self._check_triangular_bounds(var)[0]