elec_3d_2d

 elec_3d_2d - Project Cartesian 3D coordinates to a 2D plane.

 [Xt,Yt] = elec_3d_2d(X,Y,Z,Zrad)

 Project 3D electrode positions onto a 2D plane, using 
 gnomonic projection, which draws a line from a point 
 halfway between equator and south pole, through electrode, 
 to a plane tangential to north pole.

 Given:  Set of 3D Cartesian coordinates (X,Y,Z with Z > 0)
         X,Y midpoint at 0
         Zrad is radius in Z

 See also elec_2d_3d.m

0001 function [Xt,Yt] = elec_3d_2d(X,Y,Z,Zrad)
0002 
0003 % elec_3d_2d - Project Cartesian 3D coordinates to a 2D plane.
0004 %
0005 % [Xt,Yt] = elec_3d_2d(X,Y,Z,Zrad)
0006 %
0007 % Project 3D electrode positions onto a 2D plane, using
0008 % gnomonic projection, which draws a line from a point
0009 % halfway between equator and south pole, through electrode,
0010 % to a plane tangential to north pole.
0011 %
0012 % Given:  Set of 3D Cartesian coordinates (X,Y,Z with Z > 0)
0013 %         X,Y midpoint at 0
0014 %         Zrad is radius in Z
0015 %
0016 % See also elec_2d_3d.m
0017 %
0018 
0019 % $Revision: 1.1 $ $Date: 2004/11/12 01:32:33 $
0020 
0021 % Licence:  GNU GPL, no implied or express warranties
0022 % History:  10/1999, Chris Harvey
0023 %           07/2001, Darren.Weber_at_radiology.ucsf.edu
0024 %                    - using matrix algebra rather than indexed looping
0025 %
0026 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
0027 
0028 rad = Zrad / 2;
0029 
0030 t = (Z + rad) * ( 1/rad );
0031 
0032 Xt = X .* t;
0033 Yt = Y .* t;
0034 
0035 return