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

  FT_HEADMODEL_INTERPOLATE describes a volume conduction model of the head in which
  subsequent leadfield computations can be performed using a simple interpolation
  Use as
    headmodel = ft_headmodel_interpolate(filename, sens, leadfield)
    headmodel = ft_headmodel_interpolate(filename, sens, leadfield)
  The input parameters are the filename to which the model will be written,
  the electrode definition (see ft_DATATYPE_SENS). The third input argument
  is either a pre-computed leadfield structure from FT_PREPARE_LEADFIELD
  or a the output of a previous call to FT_HEADMODEL_INTERPOLATE.
  The output volume conduction model is stored on disk in a MATLAB file together with a
  number of NIFTi files. The mat file contains a structure with the following fields
    headmodel.sens        = structure, electrode sensor description, see FT_DATATYE_SENS
    headmodel.filename    = cell-array with NIFTI filenames, one file per channel
  and contains
    headmodel.dim         = [Nx Ny Nz] vector with the number of grid points along each dimension
    headmodel.transform   = 4x4 homogenous transformation matrix
    headmodel.unit        = string with the geometrical units of the positions, e.g. 'cm' or 'mm'
  to describe the source positions.