Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_convert_coordsys”.

  FT_CONVERT_COORDSYS changes the coordinate system of the input object to
  the specified coordinate system. The coordinate system of the input
  object is determined from the structure field object.coordsys, or needs to
  be determined and specified interactively by the user.
 
  Use as
    [object] = ft_convert_coordsys(object)
  to only determine the coordinate system, or
    [object] = ft_convert_coordsys(object, target)
    [object] = ft_convert_coordsys(object, target, opt)
    [object] = ft_convert_coordsys(object, target, opt, template)
  to determine and convert the coordinate system.
 
  The optional input argument opt determines the behavior when converting
  to the spm coordinate system, and pertains to the functional behaviour of
  the private functions: align_ctf2acpc and align_neuromag2acpc.
 
  The following input objects are supported
    anatomical mri, see FT_READ_MRI
    anatomical or functional atlas, see FT_READ_ATLAS
    (not yet) electrode definition
    (not yet) gradiometer array definition
    (not yet) volume conductor definition
    (not yet) dipole grid definition
 
  Possible input coordinate systems are 'ctf', 'bti', '4d', 'neuromag' and 'itab'.
  Possible target coordinate systems are 'acpc'.
 
  Note that the conversion will be an automatic one, which means that it
  will be an approximate conversion, not taking into account differences in
  individual anatomies/differences in conventions where to put the
  fiducials.
 
  See also FT_DETERMINE_COORDSYS, ALIGN_CTF2ACPC, ALIGN_NEUROMAG2ACPC, ALIGN_FSAVERAGE2MNI