International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. B. ch. 2.5, pp. 316317

In practice, an important case is where all the projection directions are orthogonal to a certain straight line: (Fig. 2.5.6.3). Here the axis of rotation or the axis of symmetry of an object is perpendicular to an electron beam. Then the threedimensional problem is reduced to the twodimensional one, since each cross section is represented by its onedimensional projections. The direction of vector τ is defined by the rotational angle ψ of a specimen: In this case, the reconstruction is carried out separately for each level : and the threedimensional structure is obtained by superposition of layers (Vainshtein et al., 1968; Vainshtein, 1978).
References
Vainshtein, B. K. (1978). Electron microscopical analysis of the threedimensional structure of biological macromolecules. In Advances in optical and electron microscopy, Vol. 7, edited by V. E. Cosslett & R. Barer, pp. 281–377. London: Academic Press.Google ScholarVainshtein, B. K., Barynin, V. V. & Gurskaya, G. V. (1968). The hexagonal crystalline structure of catalase and its molecular structure. Sov. Phys. Dokl. 13, 838–841.Google Scholar