International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2010 
International Tables for Crystallography (2010). Vol. B, ch. 2.5, p. 380
Figure 2.5.7.2
P. A. Penczek^{g}


Figure 2.5.7.2
The geometrical constraints of the 2D alignment problem. (a) The reference 2D particle is placed within a square image frame n × n pixels and its size is such that it can be bounded by a circle with a radius r no larger than 0.9n. (b) The particle projection, the size of which is bounded by the same radius as the reference view, can be located within a circle centred on discrete locations within the image frame, such that the maximum translation is k = (n/2) − r. The number of possible translations is (2k + 1)^{2}. Reprinted from Joyeux & Penczek (2002) with permission from Elsevier. 