FT_READ_SENS read sensor positions from various manufacturer specific files. See
 further down for the list of file types that are supported.

 Use as
   grad = ft_read_sens(filename, ...)  % for gradiometers
   elec = ft_read_sens(filename, ...)  % for electrodes

 Additional options should be specified in key-value pairs and can be
   'fileformat'     = string, see the list of supported file formats (the default is determined automatically)
   'senstype'       = string, can be 'eeg' or 'meg', specifies which type of sensors to read from the file (default = 'eeg')
   'coordsys'       = string, 'head' or 'dewar' (default = 'head')
   'coilaccuracy'   = can be empty or a number (0, 1 or 2) to specify the accuracy (default = [])

 An electrode definition contain the following fields
   elec.elecpos = Nx3 matrix with carthesian (x,y,z) coordinates of each
                  electrode
   elec.label   = cell-array of length N with the label of each electrode
   elec.chanpos = Nx3 matrix with coordinates of each sensor

 A gradiometer definition generally consists of multiple coils per channel, e.g. two
 coils for a 1st order gradiometer in which the orientation of the coils is
 opposite. Each coil is described separately and a large "tra" matrix has to be
 given that defines how the forward computed field is combined over the coils to
 generate the output of each channel. The gradiometer definition constsis of the
 following fields
   grad.coilpos = Mx3 matrix with the position of each coil
   grad.coilori = Mx3 matrix with the orientation of each coil
   grad.tra     = NxM matrix with the weight of each coil into each channel
   grad.label   = cell-array of length N with the label of each of the channels
   grad.chanpos = Nx3 matrix with the positions of each sensor

 Files from the following acquisition systems and analysis platforms file formats
 are supported.

   asa_elc besa_elp besa_pos besa_sfp yokogawa_ave yokogawa_con yokogawa_raw 4d
   4d_pdf 4d_m4d 4d_xyz ctf_ds ctf_res4 itab_raw itab_mhd netmeg neuromag_fif
   neuromag_mne neuromag_mne_elec neuromag_mne_grad polhemus_fil polhemus_pos
   zebris_sfp spmeeg_mat eeglab_set localite_pos artiins_oxy3 matlab

 See also FT_READ_HEADER, FT_TRANSFORM_SENS, FT_PREPARE_VOL_SENS, FT_COMPUTE_LEADFIELD,
 FT_DATATYPE_SENS