code: def extract_polygon_area(self, pid, polygon_points):
          
          polygon = shapgeo.Polygon(polygon_points)
          xy = self.grid.get_element_centroids()
          in_poly = []
          for nr, point in enumerate(xy):
              if shapgeo.Point(point).within(polygon):
                  in_poly.append(nr)
  
          values = self.parsets[pid][in_poly]
          return np.array(in_poly), values
docs: Extract all data points whose element centroid lies within the given
          polygon.
  
          Parameters
          ----------
  
          Returns
          -------