function [headmodel] = ft_read_vol(filename, varargin)

% FT_READ_VOL reads a volume conduction model from various manufacturer
% specific files. Currently supported are ASA, CTF, Neuromag, MBFYS
% and Matlab.
%
% Use as
%   headmodel = ft_read_vol(filename, ...)
%
% Additional options should be specified in key-value pairs and can be
%   'fileformat'   string
%
% The volume conduction model is represented as a structure with fields
% that depend on the type of model.
%
% See also FT_TRANSFORM_VOL, FT_PREPARE_VOL_SENS, FT_COMPUTE_LEADFIELD

% Copyright (C) 2008-2013 Robert Oostenveld
%
% This file is part of FieldTrip, see http://www.fieldtriptoolbox.org
% for the documentation and details.
%
%    FieldTrip is free software: you can redistribute it and/or modify
%    it under the terms of the GNU General Public License as published by
%    the Free Software Foundation, either version 3 of the License, or
%    (at your option) any later version.
%
%    FieldTrip is distributed in the hope that it will be useful,
%    but WITHOUT ANY WARRANTY; without even the implied warranty of
%    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%    GNU General Public License for more details.
%
%    You should have received a copy of the GNU General Public License
%    along with FieldTrip. If not, see <http://www.gnu.org/licenses/>.
%
% $Id$

% optionally get the data from the URL and make a temporary local copy
filename = fetch_url(filename);

% test whether the file exists
if ~exist(filename)
  error(sprintf('file ''%s'' does not exist', filename));
end

% get the options
fileformat = ft_getopt(varargin, 'fileformat', ft_filetype(filename));

switch fileformat
  case 'matlab'
    % FIXME in the future the file should contain the variable 'headmodel' instead of vol
    headmodel = loadvar(filename, 'vol');

  case 'ctf_hdm'
    headmodel = read_ctf_hdm(filename);

  case 'asa_vol'
    headmodel = read_asa_vol(filename);
    headmodel.type = 'asa';

  case 'mbfys_ama'
    ama = loadama(filename);
    headmodel = ama2vol(ama);

  otherwise
    error('unknown fileformat for volume conductor model');
end

% this will ensure that the structure is up to date, e.g. that the type is correct and that it has units
headmodel = ft_datatype_headmodel(headmodel);