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Figure 1
The projection scheme, visualized using the example of a single-stranded helix. For such seemingly endless geometries, there is a building block (upper left-hand corner) that is recurrent along the z axis (see full helix on the right). For a full body consisting of M stacked building blocks, one finds distinct structural motifs, such as the building block itself, neighbouring building blocks, single-spaced building blocks and so on up to (M − 1)-spaced building blocks. The scattering intensity of the full geometry can hence be calculated by summing the contributions of these structural motifs, scaled by their recurrence. This bypasses the demand for an actual DA model representing the full structure, as we solely evaluate projections of the building block instead of actual stacked duplicates, hence the term projection scheme.

IUCrJ
Volume 5| Part 4| July 2018| Pages 390-401
ISSN: 2052-2525
https://doi.org/10.1107/S2052252518005493