| pic3_rays 
 | 
             rays= pic3_rays(xpict, ypict, ray)  
          or rays= pic3_rays(xpict, ypict, ray, q_up)  
 
     Like picture_rays, but returns rays in the [p,q] representation  
     appropriate for hex5_track.  
     (XPICT,YPICT) are 2D arrays of pixel corners in the image plane;  
     RAY is the central ray (0,0) in (XPICT,YPICT) coordinates, given  
     in [p,q] representation (i.e. RAY is a 3-by-2 array).  The  
     optional Q_UP is a 3-vector specifying the orientation of the  
     y-axis in the picture plane (see theta_up, phi_up in picture_rays  
     for a description of default orientation).  Q_UP must not be  
     parallel to RAY(,2).  
interpreted function, defined at i0/hex.i   line 94  
 |