Thanks roy.granit for the answer. I have read material on the two techniques you mentioned. I think i need to refine my question. I understood the process that is based on the x-ray or NMR based techniques. However for the third method based on cryo electron density images, that i am not able to find the material. I am basically looking at the computations that are involved. can you help me something on that? Or could you suggest some good references? your inputs are valuable to me.
Thank you