code: def modify_area(self, pid, xmin, xmax, zmin, zmax, value):
          
          area_polygon = shapgeo.Polygon(
              ((xmin, zmax), (xmax, zmax), (xmax, zmin), (xmin, zmin))
          )
          self.modify_polygon(pid, area_polygon, value)
docs: Modify the given dataset in the rectangular area given by the
          parameters and assign all parameters inside this area the given value.
  
          Partially contained elements are treated as INSIDE the area, i.e., they
          are assigned new values.
  
          Parameters
          ----------
          pid: int
              id of the parameter set to modify
          xmin: float
              smallest x value of the area to modify
          xmax: float
              largest x value of the area to modify
          zmin: float
              smallest z value of the area to modify
          zmin: float
              largest z value of the area to modify
          value: float
              this value is assigned to all parameters of the area
  
          Examples
          --------
  
          >>> import crtomo.tdManager as CRtdm
              tdman = CRtdm.tdMan(
                      elem_file='GRID/elem.dat',
                      elec_file='GRID/elec.dat',
              )
              pid = tdman.parman.add_empty_dataset(value=1)
              tdman.parman.modify_area(
                      pid,
                      xmin=0,
                      xmax=2,
                      zmin=-2,
                      zmin=-0.5,
                      value=2,
              )
              fig, ax = tdman.plot.plot_elements_to_ax(pid)
              fig.savefig('out.png')