sensor_planar

(Toolbox/sensor_planar.m in BrainStorm 2.0 (Alpha))

Function Synopsis

[R,s,u1,u2] = sensor_planar(R1,baseline);

Help Text

SENSOR_PLANAR - Generate planar gradiometers
 function [R,s,u1,u2] = sensor_planar(R1,baseline);
 Given sensor sites in R1, generate planar point gradiometers, 
  oriented in directions orthogonal to R1 with a separation of baseline.
  Optionally, if R1 has six columns, the last three are presumed to be the
  desired planar normal.
 
 For example, the Neuromag 122 system can be roughly approximated by
 spacing the sensors approximately 3 cm apart on a 10.5 cm shell, with
 a 1.5 cm baseline, for a total of 78 sensors about the entire hemisphere.
 R1 = sensor_ring(0.105,16.6*pi/180,6);  % generate sensor sites
 [R,s] = sensor_planar(R1,[0.015]);

 The first three columns of R and s will be the positions of the coils
   to one side of R1.  The next three columns correspond to the second coil in
   each sensor, a distance of baseline away.  The combined set for a channel.

 If R1 has mR rows, then R will have mR*2 rows.  Each pair of rows
  corresponds to the primary and secondary channels at each site in R1.
  where the secondary channel is oriented orthogonal
  to the primary channel.
 s will give the unit radial direction of R1/norm(R1).

 U1 and U2 are calculated from spherical coordinates.
 Each row of u1 will give the theta direction of the primary channel.
 Each row of u2 will give the phi direction of the secondary channel.
 Each row of u1 and u2 is orthogonal to each other and 
  the corresponding direction in R1.

 See also SENSOR_RING, SENSOR_AXIAL, SENSOR_122

Cross-Reference Information

simulator                          C:\BrainStorm_2001\Toolbox\simulator.m

Listing of function C:\BrainStorm_2001\Toolbox\sensor_planar.m

function [R,s,u1,u2] = sensor_planar(R1,baseline);
%SENSOR_PLANAR - Generate planar gradiometers
% function [R,s,u1,u2] = sensor_planar(R1,baseline);
% Given sensor sites in R1, generate planar point gradiometers, 
%  oriented in directions orthogonal to R1 with a separation of baseline.
%  Optionally, if R1 has six columns, the last three are presumed to be the
%  desired planar normal.
% 
% For example, the Neuromag 122 system can be roughly approximated by
% spacing the sensors approximately 3 cm apart on a 10.5 cm shell, with
% a 1.5 cm baseline, for a total of 78 sensors about the entire hemisphere.
% R1 = sensor_ring(0.105,16.6*pi/180,6);  % generate sensor sites
% [R,s] = sensor_planar(R1,[0.015]);
%
% The first three columns of R and s will be the positions of the coils
%   to one side of R1.  The next three columns correspond to the second coil in
%   each sensor, a distance of baseline away.  The combined set for a channel.
%
% If R1 has mR rows, then R will have mR*2 rows.  Each pair of rows
%  corresponds to the primary and secondary channels at each site in R1.
%  where the secondary channel is oriented orthogonal
%  to the primary channel.
% s will give the unit radial direction of R1/norm(R1).
%
% U1 and U2 are calculated from spherical coordinates.
% Each row of u1 will give the theta direction of the primary channel.
% Each row of u2 will give the phi direction of the secondary channel.
% Each row of u1 and u2 is orthogonal to each other and 
%  the corresponding direction in R1.
%
% See also SENSOR_RING, SENSOR_AXIAL, SENSOR_122

%<autobegin> ---------------------- 26-May-2004 11:34:20 -----------------------
% --------- Automatically Generated Comments Block Using AUTO_COMMENTS ---------
%
% CATEGORY: Forward Modeling
%
% At Check-in: $Author: Mosher $  $Revision: 14 $  $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 11:34:20 -----------------------

% ----------------------------- Script History ---------------------------------
% 1994 by John C. Mosher, Ph.D.
% 19-May-2004 JCM Comments Cleaning
% ----------------------------- Script History ---------------------------------

mR = size(R1,1);        % number of sensors
nCoils = 2;            % two per channel in planar config


% generate primary and secondary directions
if(size(R1,2) == 6),        % user has supplied desired orientation
  [ph,th,ra] = cart2sph(R1(:,4),R1(:,5),R1(:,6));
  s1 = R1(:,4:6);
else
  % get spherical coordinates for rho, theta, phi
  [ph,th,ra] = cart2sph(R1(:,1),R1(:,2),R1(:,3));
  % generate radial vectors
  s1 = R1 ./ (ra(:,[1 1 1]));     % normalized radial orientation
end

% th is returned as elevation from xy plane.  Convert to angle from z-axis.
th = pi/2 - th;

% generate primary in theta direction
u1 = [cos(th).*cos(ph) cos(th).*sin(ph) -sin(th)];

% generate secondary in the phi direction
u2 = [-sin(ph) cos(ph) zeros(mR,1)];

% primary channels
pR = [(R1(:,1:3) + baseline*u1/2) (R1(:,1:3) - baseline*u1/2)];
% secondary channels
sR = [(R1(:,1:3) + baseline*u2/2) (R1(:,1:3) - baseline*u2/2)];

% interleave
R([[1:2:(mR*2)] [2:2:(mR*2)]],:) = [pR;sR];
s([[1:2:(mR*2)] [2:2:(mR*2)]],:) = [s1 s1;s1 s1];

return