docs: def long_id(self, sample):
          ''' Return the corresponding longitude
  
          Args:
              sample (int): sample number on a line
  
          Returns:
              Correponding longidude in degree
          '''
          if self.grid == 'WAC':
              lon = self.CENTER_LONGITUDE + (sample - self.SAMPLE_PROJECTION_OFFSET - 1)\
                  * self.MAP_SCALE * 1e-3 / (self.A_AXIS_RADIUS * np.cos(self.CENTER_LATITUDE * np.pi / 180.0))
              return lon * 180 / np.pi
          else:
              lon = float(self.CENTER_LONGITUDE) + \
                  (sample - float(self.SAMPLE_PROJECTION_OFFSET) - 1)\
                  / float(self.MAP_RESOLUTION)
              return lon