function diameter = computeFeretHrep(hrep, dirMatrix, zerotol)
% compute the Feret diameter for a H-polytope in given direction
%
% Syntax: diameter = computeFeretVrep(vrep, dirMatrix)
% 
% This function calculates the Feret diameter for all directions in 
%   dirMatrix that contains one direction in each row. The Feret diameter 
%   is the 1-dimensional volume of the projection of the polytope onto a
%   line with the given direction. By this definition the Feret diameter is
%   also known as quermass like the projection area.
%
% computeFeretVrep(..., zerotol) allows to set the tolerance for 
%   underlying algorithms. Default: elkZerotol
%
% See also: computeFeretVrep, computeProjectionAreaHrep, computeVolumeHrep,
%   computeSupportValueHrep, computeFacetAreaHrep

% The elk-library: convex geometry applied to crystallization modeling.
%   Copyright (C) 2012 Alexander Reinhold
%
% This program 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.
%
% This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

%% Input handling
% default zerotol
if ~exist('zerotol', 'var')
    zerotol = elkZerotol;
end

%% Calculating area
% fall back to computeMeanWidthHrep
vrep = convertHrepToVrep(hrep, zerotol);
if ~isempty(vrep.V)
    diameter = computeFeretVrep(vrep, dirMatrix);
else
    diameter = 0;
end