function unit = ft_estimate_units(size)

% FT_ESTIMATE_UNITS tries to determine the units of a geometrical object by

% looking at its size and by relating this to the approximate size of the

% human head according to the following table:

% from 0.050 to 0.500 -> meter

% from 0.500 to 5.000 -> decimeter

% from 5.000 to 50.000 -> centimeter

% from 50.000 to 500.000 -> millimeter

%

% Use as

% unit = ft_estimate_units(size)

%

% This function will return one of the following strings

% 'm'

% 'cm'

% 'mm'

%

% See also FT_CONVERT_UNITS

% Copyright (C) 2009-2013, 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/>.

%

% $Id$

% the objects size should be estimated outside this function

assert(isscalar(size), 'the size should be a scalar');

% do some magic based on the size

unit = {'m', 'dm', 'cm', 'mm'};

est = log10(size)+1.8;

indx = round(est);

if indx>length(unit)

indx = length(unit);

ft_warning('assuming that the units are "%s"', unit{indx});

elseif indx<1

indx = 1;

ft_warning('assuming that the units are "%s"', unit{indx});

elseif abs((est-floor(est)) - 0.5)<0.1

% the size estimate falls within the expected range, but is not very decisive

% for example round(1.49) results in meter, but round(1.51) results in decimeter

ft_warning('the estimated units are not very decisive, assuming that the units are "%s"', unit{indx});

end

unit = unit{indx};