docs: def write_observation_zone(self, num, **kw):
  
          """
          Write observation zone information for a taskpoint::
  
              writer.write_task_options(
                  start_time=time(12, 34, 56),
                  task_time=timedelta(hours=1, minutes=45, seconds=12),
                  waypoint_distance=False,
                  distance_tolerance=(0.7, 'km'),
                  altitude_tolerance=300.0,
              )
              # -> Options,NoStart=12:34:56,TaskTime=01:45:12,WpDis=False,NearDis=0.7km,NearAlt=300.0m
  
          :param num: consecutive number of a waypoint (``0``: Start)
          :param style: direction (``0``: Fixed value, ``1``: Symmetrical, ``2``:
              To next point, ``3``: To previous point, ``4``: To start point
          :param radius: radius 1 in meter or as ``(radius, unit)`` tuple
          :param angle: angle 1 in degrees
          :param radius2: radius 2 in meter or as ``(radius, unit)`` tuple
          :param angle 2: angle 2 in degrees
          :param angle12: angle 12 in degress
          :param line: should be ``True`` if start or finish line
          """
  
          if not self.in_task_section:
              raise RuntimeError(
                  u'Observation zones have to be written in task section')
  
          fields = [u'ObsZone=%d' % num]
  
          if 'style' in kw:
              fields.append(u'Style=%d' % kw['style'])
  
          if 'radius' in kw:
              fields.append(u'R1=' + self.format_distance(kw['radius']))
  
          if 'angle' in kw:
              fields.append(u'A1=' + self.format_angle(kw['angle']))
  
          if 'radius2' in kw:
              fields.append(u'R2=' + self.format_distance(kw['radius2']))
  
          if 'angle2' in kw:
              fields.append(u'A2=' + self.format_angle(kw['angle2']))
  
          if 'angle12' in kw:
              fields.append(u'A12=' + self.format_angle(kw['angle12']))
  
          if 'line' in kw:
              fields.append(u'Line=' + ('1' if kw['line'] else '0'))
  
          self.write_fields(fields)