"blending position"

Hi! I wrote a program to simulate radiography based on 3d texture and blending. here the thread–> http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=233274&fpart=1, If I want to change the position of the “ray producer” in my program what I have to do? is it enough change the viewpoint position?