code: def get_cell_shift(flow_model):
          
          assert flow_model.lower() in FlowModelConst.d8_deltas
          return FlowModelConst.d8_deltas.get(flow_model.lower())
docs: Get flow direction induced cell shift dict.
          Args:
              flow_model: Currently, "TauDEM", "ArcGIS", and "Whitebox" are supported.