class_docstr: SEVIRI HRIT prologue reader.
class_docstr_tok: ["SEVIRI","HRIT","prologue","reader","."]
docstr: Get earth radii from prologue.
  
  Returns:
      Equatorial radius, polar radius [m]
code: def get_earth_radii(self):
      """Get earth radii from prologue.
  
      Returns:
          Equatorial radius, polar radius [m]
  
      """
      earth_model = self.prologue["GeometricProcessing"]["EarthModel"]
      a = earth_model["EquatorialRadius"] * 1000
      b = (
          (
              earth_model["NorthPolarRadius"]
              + earth_model["SouthPolarRadius"]
          )
          / 2.0
          * 1000
      )
      return a, b
  
imports: from __future__ import division
  import copy
  import logging
  from datetime import timedelta
  import dask.array
  import numpy
  import xarray
  from pyresample import geometry
  import satpy.readers.utils
  from satpy._compat import cached_property
  from satpy.readers._geos_area import get_area_definition, get_area_extent, get_geos_area_naming
  from satpy.readers.eum_base import get_service_mode, recarray2dict, time_cds_short
  from satpy.readers.hrit_base import HRITFileHandler, ancillary_text, annotation_header, base_hdr_map, image_data_function
  from satpy.readers.seviri_base import CHANNEL_NAMES, HRV_NUM_COLUMNS, REPEAT_CYCLE_DURATION, SATNUM, NoValidOrbitParams, OrbitPolynomialFinder, SEVIRICalibrationHandler, add_scanline_acq_time, create_coef_dict, get_cds_time, get_satpos, mask_bad_quality, pad_data_horizontally, round_nom_time
  from satpy.readers.seviri_l1b_native_hdr import hrit_epilogue, hrit_prologue, impf_configuration
  from satpy.utils import get_legacy_chunk_size
label_desc: Use image node_id 4 for calling the HRITMSGPrologueFileHandler obj's underlying member method code with example usage: obj.get_earth_radii() and returns: a,  b