docs: def add_footpoint_and_equatorial_drifts(inst, equ_mer_scalar='equ_mer_drifts_scalar',
                                                equ_zonal_scalar='equ_zon_drifts_scalar',
                                                north_mer_scalar='north_footpoint_mer_drifts_scalar',
                                                north_zon_scalar='north_footpoint_zon_drifts_scalar',
                                                south_mer_scalar='south_footpoint_mer_drifts_scalar',
                                                south_zon_scalar='south_footpoint_zon_drifts_scalar',
                                                mer_drift='iv_mer',
                                                zon_drift='iv_zon'):
      """Translates geomagnetic ion velocities to those at footpoints and magnetic equator.
      Note
      ----
          Presumes scalar values for mapping ion velocities are already in the inst, labeled
          by north_footpoint_zon_drifts_scalar, north_footpoint_mer_drifts_scalar,
          equ_mer_drifts_scalar, equ_zon_drifts_scalar.
      
          Also presumes that ion motions in the geomagnetic system are present and labeled
          as 'iv_mer' and 'iv_zon' for meridional and zonal ion motions.
          
          This naming scheme is used by the other pysat oriented routines
          in this package.
      
      Parameters
      ----------
      inst : pysat.Instrument
      equ_mer_scalar : string
          Label used to identify equatorial scalar for meridional ion drift
      equ_zon_scalar : string
          Label used to identify equatorial scalar for zonal ion drift
      north_mer_scalar : string
          Label used to identify northern footpoint scalar for meridional ion drift
      north_zon_scalar : string
          Label used to identify northern footpoint scalar for zonal ion drift
      south_mer_scalar : string
          Label used to identify northern footpoint scalar for meridional ion drift
      south_zon_scalar : string
          Label used to identify southern footpoint scalar for zonal ion drift
      mer_drift : string
          Label used to identify meridional ion drifts within inst
      zon_drift : string
          Label used to identify zonal ion drifts within inst
          
      Returns
      -------
      None
          Modifies pysat.Instrument object in place. Drifts mapped to the magnetic equator
          are labeled 'equ_mer_drift' and 'equ_zon_drift'. Mappings to the northern
          and southern footpoints are labeled 'south_footpoint_mer_drift' and
          'south_footpoint_zon_drift'. Similarly for the northern hemisphere.
      """
  
      inst['equ_mer_drift'] = {'data' : inst[equ_mer_scalar]*inst[mer_drift],
                              'units':'m/s',
                              'long_name':'Equatorial meridional ion velocity',
                              'notes':('Velocity along meridional direction, perpendicular '
                                      'to field and within meridional plane, scaled to '
                                      'magnetic equator. Positive is up at magnetic equator. '
                                      'Velocity obtained using ion velocities relative '
                                      'to co-rotation in the instrument frame along '
                                      'with the corresponding unit vectors expressed in '
                                      'the instrument frame. Field-line mapping and '
                                      'the assumption of equi-potential field lines '
                                      'is used to translate the locally measured ion '
                                      'motion to the magnetic equator. The mapping '
                                      'is used to determine the change in magnetic '
                                      'field line distance, which, under assumption of '
                                      'equipotential field lines, in turn alters '
                                      'the electric field at that location (E=V/d). '),
                              'label':'Equatorial Meridional Ion Velocity',
                              'axis':'Equatorial Meridional Ion Velocity',
                              'desc':'Equatorial Meridional Ion Velocity',
                              'scale':'Linear',
                              'value_min':-500., 
                              'value_max':500.}
  
      inst['equ_zon_drift'] = {'data' : inst[equ_zonal_scalar]*inst[zon_drift],
                              'units':'m/s',
                              'long_name':'Equatorial zonal ion velocity',
                              'notes':('Velocity along zonal direction, perpendicular '
                                      'to field and the meridional plane, scaled to '
                                      'magnetic equator. Positive is generally eastward. '
                                      'Velocity obtained using ion velocities relative '
                                      'to co-rotation in the instrument frame along '
                                      'with the corresponding unit vectors expressed in '
                                      'the instrument frame. Field-line mapping and '
                                      'the assumption of equi-potential field lines '
                                      'is used to translate the locally measured ion '
                                      'motion to the magnetic equator. The mapping '
                                      'is used to determine the change in magnetic '
                                      'field line distance, which, under assumption of '
                                      'equipotential field lines, in turn alters '
                                      'the electric field at that location (E=V/d). '),
                              'label':'Equatorial Zonal Ion Velocity',
                              'axis':'Equatorial Zonal Ion Velocity',
                              'desc':'Equatorial Zonal Ion Velocity',
                              'scale':'Linear',
                              'value_min':-500., 
                              'value_max':500.}
  
      inst['south_footpoint_mer_drift'] = {'data' : inst[south_mer_scalar]*inst[mer_drift],
                              'units':'m/s',
                              'long_name':'Southern meridional ion velocity',
                              'notes':('Velocity along meridional direction, perpendicular '
                                      'to field and within meridional plane, scaled to '
                                      'southern footpoint. Positive is up at magnetic equator. '
                                      'Velocity obtained using ion velocities relative '
                                      'to co-rotation in the instrument frame along '
                                      'with the corresponding unit vectors expressed in '
                                      'the instrument frame. Field-line mapping and '
                                      'the assumption of equi-potential field lines '
                                      'is used to translate the locally measured ion '
                                      'motion to the magnetic footpoint. The mapping '
                                      'is used to determine the change in magnetic '
                                      'field line distance, which, under assumption of '
                                      'equipotential field lines, in turn alters '
                                      'the electric field at that location (E=V/d). '),
                              'label':'Southern Meridional Ion Velocity',
                              'axis':'Southern Meridional Ion Velocity',
                              'desc':'Southern Meridional Ion Velocity',
                              'scale':'Linear',
                              'value_min':-500., 
                              'value_max':500.}
  
      inst['south_footpoint_zon_drift'] = {'data':inst[south_zon_scalar]*inst[zon_drift],
                              'units':'m/s',
                              'long_name':'Southern zonal ion velocity',
                              'notes':('Velocity along zonal direction, perpendicular '
                                      'to field and the meridional plane, scaled to '
                                      'southern footpoint. Positive is generally eastward. '
                                      'Velocity obtained using ion velocities relative '
                                      'to co-rotation in the instrument frame along '
                                      'with the corresponding unit vectors expressed in '
                                      'the instrument frame. Field-line mapping and '
                                      'the assumption of equi-potential field lines '
                                      'is used to translate the locally measured ion '
                                      'motion to the southern footpoint. The mapping '
                                      'is used to determine the change in magnetic '
                                      'field line distance, which, under assumption of '
                                      'equipotential field lines, in turn alters '
                                      'the electric field at that location (E=V/d). '),
                              'label':'Southern Zonal Ion Velocity',
                              'axis':'Southern Zonal Ion Velocity',
                              'desc':'Southern Zonal Ion Velocity',
                              'scale':'Linear',
                              'value_min':-500., 
                              'value_max':500.}
  
      inst['north_footpoint_mer_drift'] = {'data':inst[north_mer_scalar]*inst[mer_drift],
                              'units':'m/s',
                              'long_name':'Northern meridional ion velocity',
                              'notes':('Velocity along meridional direction, perpendicular '
                                      'to field and within meridional plane, scaled to '
                                      'northern footpoint. Positive is up at magnetic equator. '
                                      'Velocity obtained using ion velocities relative '
                                      'to co-rotation in the instrument frame along '
                                      'with the corresponding unit vectors expressed in '
                                      'the instrument frame. Field-line mapping and '
                                      'the assumption of equi-potential field lines '
                                      'is used to translate the locally measured ion '
                                      'motion to the magnetic footpoint. The mapping '
                                      'is used to determine the change in magnetic '
                                      'field line distance, which, under assumption of '
                                      'equipotential field lines, in turn alters '
                                      'the electric field at that location (E=V/d). '),
                              'label':'Northern Meridional Ion Velocity',
                              'axis':'Northern Meridional Ion Velocity',
                              'desc':'Northern Meridional Ion Velocity',
                              'scale':'Linear',
                              'value_min':-500., 
                              'value_max':500.}
  
      inst['north_footpoint_zon_drift'] = {'data':inst[north_zon_scalar]*inst[zon_drift],
                              'units':'m/s',
                              'long_name':'Northern zonal ion velocity',
                              'notes':('Velocity along zonal direction, perpendicular '
                                      'to field and the meridional plane, scaled to '
                                      'northern footpoint. Positive is generally eastward. '
                                      'Velocity obtained using ion velocities relative '
                                      'to co-rotation in the instrument frame along '
                                      'with the corresponding unit vectors expressed in '
                                      'the instrument frame. Field-line mapping and '
                                      'the assumption of equi-potential field lines '
                                      'is used to translate the locally measured ion '
                                      'motion to the northern footpoint. The mapping '
                                      'is used to determine the change in magnetic '
                                      'field line distance, which, under assumption of '
                                      'equipotential field lines, in turn alters '
                                      'the electric field at that location (E=V/d). '),
                              'label':'Northern Zonal Ion Velocity',
                              'axis':'Northern Zonal Ion Velocity',
                              'desc':'Northern Zonal Ion Velocity',
                              'scale':'Linear',
                              'value_min':-500., 
                              'value_max':500.}