elec_sph2cart

 elec_sph2cart - convert spherical to Cartesian coordinates

 Convert from spherical (theta,phi,r) to Cartesian rectangular (x,y,z)
 coordinates.

 Useage: [X,Y,Z] = elec_sph2cart(theta,phi,r,[degrees])

           theta is counterclockwise rotation from +x in x-y plane (azimuth),
           phi is elevation with respect to z-axis (eg, Cz in 10-20 system),
           r is radius,
           degrees: 0=radians (default) or 1=degrees for theta & phi
 
 Result:   (X,Y,Z) are double floating point
           
 Note:     Conversion from spherical to Cartesian coordinates, given
           angles in radians, is:

           x = r .* sin(phi) .* cos(theta);
           y = r .* sin(phi) .* sin(theta);
           z = r .* cos(phi);

           +ve x-axis from origin through T4 (right ear)
           +ve y-axis from origin through Nasion (at theta = +90degrees)

           Results from this routine are not the same as those from
           the inbuilt sph2cart matlab function. Phi here is 
           elevation with respect to z-axis.  The matlab function 
           sph2cart uses elevation with respect to xy plane.

0001 function [X,Y,Z] = elec_sph2cart(theta,phi,r,degrees)
0002 
0003 % elec_sph2cart - convert spherical to Cartesian coordinates
0004 %
0005 % Convert from spherical (theta,phi,r) to Cartesian rectangular (x,y,z)
0006 % coordinates.
0007 %
0008 % Useage: [X,Y,Z] = elec_sph2cart(theta,phi,r,[degrees])
0009 %
0010 %           theta is counterclockwise rotation from +x in x-y plane (azimuth),
0011 %           phi is elevation with respect to z-axis (eg, Cz in 10-20 system),
0012 %           r is radius,
0013 %           degrees: 0=radians (default) or 1=degrees for theta & phi
0014 %
0015 % Result:   (X,Y,Z) are double floating point
0016 %
0017 % Note:     Conversion from spherical to Cartesian coordinates, given
0018 %           angles in radians, is:
0019 %
0020 %           x = r .* sin(phi) .* cos(theta);
0021 %           y = r .* sin(phi) .* sin(theta);
0022 %           z = r .* cos(phi);
0023 %
0024 %           +ve x-axis from origin through T4 (right ear)
0025 %           +ve y-axis from origin through Nasion (at theta = +90degrees)
0026 %
0027 %           Results from this routine are not the same as those from
0028 %           the inbuilt sph2cart matlab function. Phi here is
0029 %           elevation with respect to z-axis.  The matlab function
0030 %           sph2cart uses elevation with respect to xy plane.
0031 %
0032 
0033 % $Revision: 1.1 $ $Date: 2004/11/12 01:32:34 $
0034 
0035 % Licence:  GNU GPL, no express or implied warranties
0036 % History:  07/2001, Darren.Weber_at_radiology.ucsf.edu
0037 %           08/2003, Darren.Weber_at_radiology.ucsf.edu
0038 %                    changed input option 'angle' to 'degrees' so
0039 %                    the logic below is clearer.
0040 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0041 
0042 if ~exist('degrees','var'), degrees = 0; end
0043 
0044 if degrees,
0045    % convert theta and phi from degrees to radians
0046    theta = theta * (pi/180);
0047    phi   = phi   * (pi/180);
0048 end
0049 
0050 X = r .* sin(phi) .* cos(theta);
0051 Y = r .* sin(phi) .* sin(theta);
0052 Z = r .* cos(phi);
0053 
0054 return