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# tri_area

## (Toolbox/tri_area.m in BrainStorm 2.0 (Alpha))

### Function Synopsis

    [Area] = tri_area(faces,verts);

### Help Text

    TRI_AREA - Find areas of all triangles
     function [Area] = tri_area(faces,verts);
     faces is poly x number of poly (e.g. 1000 x 3);
     verts is number of verts x 3
     Returns Area of each triangle, which can be used in subsequent calls

     See also TESSELLATION_STATS

### Cross-Reference Information

This function is called by

    manage_corticalscouts              C:\BrainStorm_2001\Toolbox\manage_corticalscouts.m

### Listing of function C:\BrainStorm_2001\Toolbox\tri_area.m

    function [Area] = tri_area(faces,verts);
    %TRI_AREA - Find areas of all triangles
    % function [Area] = tri_area(faces,verts);
    % faces is poly x number of poly (e.g. 1000 x 3);
    % verts is number of verts x 3
    % Returns Area of each triangle, which can be used in subsequent calls
    %
    % See also TESSELLATION_STATS

    %<autobegin> ---------------------- 26-May-2004 11:34:40 -----------------------
    % --------- Automatically Generated Comments Block Using AUTO_COMMENTS ---------
    %
    % CATEGORY: Utility - Numeric
    %
    % Subfunctions in this file, in order of occurrence in file:
    %   c = cross(a,b);
    %
    % At Check-in: $Author: Mosher $  $Revision: 8 $  $Date: 5/26/04 10:02a $
    %
    % This software is part of BrainStorm Toolbox Version 2.0 (Alpha) 24-May-2004
    %
    % Principal Investigators and Developers:
    % ** Richard M. Leahy, PhD, Signal & Image Processing Institute,
    %    University of Southern California, Los Angeles, CA
    % ** John C. Mosher, PhD, Biophysics Group,
    %    Los Alamos National Laboratory, Los Alamos, NM
    % ** Sylvain Baillet, PhD, Cognitive Neuroscience & Brain Imaging Laboratory,
    %    CNRS, Hopital de la Salpetriere, Paris, France
    %
    % See BrainStorm website at http://neuroimage.usc.edu for further information.
    %
    % Copyright (c) 2004 BrainStorm by the University of Southern California
    % This software distributed  under the terms of the GNU General Public License
    % as published by the Free Software Foundation. Further details on the GPL
    % license can be found at http://www.gnu.org/copyleft/gpl.html .
    %
    % FOR RESEARCH PURPOSES ONLY. THE SOFTWARE IS PROVIDED "AS IS," AND THE
    % UNIVERSITY OF SOUTHERN CALIFORNIA AND ITS COLLABORATORS DO NOT MAKE ANY
    % WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO WARRANTIES OF
    % MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, NOR DO THEY ASSUME ANY
    % LIABILITY OR RESPONSIBILITY FOR THE USE OF THIS SOFTWARE.
    %<autoend> ------------------------ 26-May-2004 11:34:40 -----------------------

    % ----------------------------- Script History ---------------------------------
    % JCM 19-May-2004  Updating comments
    % ----------------------------- Script History ---------------------------------

    % calculate the areas on all triangles
    r12 = verts(faces(:,1),:); % temporary holding
    r13 = verts(faces(:,3),:) - r12; % negative of r31
    r12 = verts(faces(:,2),:) - r12;            % from 1 to 2

    Area = sqrt(sum(cross(r12',r13').^2,1))/2;  % area of each triangle

    return

    function c = cross(a,b);
    c = [a(2,:).*b(3,:)-a(3,:).*b(2,:)
      a(3,:).*b(1,:)-a(1,:).*b(3,:)
      a(1,:).*b(2,:)-a(2,:).*b(1,:)];
    return

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