code: def dovandamme(vgp_df):
      
      vgp_df['delta'] = 90.-vgp_df['vgp_lat'].values
      ASD = np.sqrt(np.sum(vgp_df.delta**2)/(vgp_df.shape[0]-1))
      A = 1.8 * ASD + 5.
      delta_max = vgp_df.delta.max()
      while delta_max > A:
          delta_max = vgp_df.delta.max()
          if delta_max < A:
              return vgp_df, A, ASD
          vgp_df = vgp_df[vgp_df.delta < delta_max]
          ASD = np.sqrt(np.sum(vgp_df.delta**2)/(vgp_df.shape[0]-1))
          A = 1.8 * ASD + 5.
docs: determine the S_b value for VGPs using the Vandamme (1994) method
      for determining cutoff value for "outliers".
      Parameters
      ___________
      vgp_df : pandas DataFrame with required column "vgp_lat"
               This should be in the desired coordinate system and assumes one polarity
  
      Returns
      _________
      vgp_df : after applying cutoff
      cutoff : colatitude cutoff
      S_b : S_b of vgp_df  after applying cutoff