hexgrid

 function xyz=hexgrid(lside, nx, ny)

 Return the relative coordinates of a hex 'grid' centered at 0,0, of
 half-width nx x ny (see gethex())

 Inputs:

   lside - The length of a hex side, in radians

   nx    - The half-width of the hex grid.  An integral number of
           pointings, spaced along a great circle

   ny    - The half-width of the hex grid.  An integral number of
           pointings, spaced along the perpendicular great circle

 Outputs:

   xyz  - The XYZ coordinates of the hex vertices

 (EML)

0001 function xyz=hexgrid(lside, nx, ny)
0002 
0003 % function xyz=hexgrid(lside, nx, ny)
0004 %
0005 % Return the relative coordinates of a hex 'grid' centered at 0,0, of
0006 % half-width nx x ny (see gethex())
0007 %
0008 % Inputs:
0009 %
0010 %   lside - The length of a hex side, in radians
0011 %
0012 %   nx    - The half-width of the hex grid.  An integral number of
0013 %           pointings, spaced along a great circle
0014 %
0015 %   ny    - The half-width of the hex grid.  An integral number of
0016 %           pointings, spaced along the perpendicular great circle
0017 %
0018 % Outputs:
0019 %
0020 %   xyz  - The XYZ coordinates of the hex vertices
0021 %
0022 % (EML)
0023 
0024 ixmin = -2*nx;
0025 ixmax =  2*nx;
0026 iymin =   -ny;
0027 iymax =    ny;
0028 
0029 hside = lside * cos(pi/6);
0030 
0031 iv=1;
0032 for iy=iymin:iymax
0033    
0034   if(mod(iy, 2)==0)
0035     ixmintmp = ixmin;
0036   else
0037     ixmintmp = ixmin+1;
0038   end
0039 
0040   for ix=ixmintmp:2:ixmax
0041 
0042 % I flipped these around to have the shorter spacing along lines of
0043 % constant dec
0044 
0045     dy        = lside/2 * ix;
0046     dx        = hside   * iy;
0047 
0048     xv(iv)    = dx;
0049     yv(iv)    = dy;
0050 
0051     theta(iv) = atan2(dy, dx);
0052 
0053     darc(iv)  = sqrt(dx*dx + dy*dy);
0054 
0055     r(iv) = sin(darc(iv));
0056 
0057     xt(iv) = r(iv) * cos(theta(iv));
0058     yt(iv) = r(iv) * sin(theta(iv));
0059     zt(iv) = cos(darc(iv));
0060 
0061     iv = iv+1;
0062   end
0063 
0064 end
0065 
0066 xyz = [xt; yt; zt];
0067 
0068 return