Jungfraujoch/docs/CPU_DATA_ANALYSIS.md

CPU-side crystallographic data analysis (Jungfraujoch)

This document describes the crystallographic algorithms implemented in Jungfraujoch for CPU- and GPU-side real‑time and near‑real‑time data analysis.

Scope. The pipeline covered here comprises:

1. geometry mapping and corrections,
2. azimuthal integration (powder/radial profiles),
3. Bragg spot finding (strong pixels → connected components → spot descriptors),
4. indexing (still and rotation modes),
5. Bravais lattice / centering inference,
6. geometry and lattice refinement,
7. reflection prediction (still and rotation),
8. Bragg integration by either 2D box summation or profile fitting (Kabsch, reference-free),
9. scaling and merging,
10. merge-level error modelling, outlier rejection and the resolution cutoff,
11. space-group determination from the merged intensities (Laue group, screw axes, centering) and the twinning check,
12. auxiliary statistics (Wilson plot, ⟨I/σ(I)⟩, CC1/2, CCref),
13. amplitude estimation (French–Wilson) and R-free test-set flagging,
14. optional model-based validation: R-free against a supplied model, 2Fo−Fc / Fo−Fc electron-density maps, and an anomalous difference map with the strongest anomalous sites named.

The reference is split into four parts, in pipeline order; the section numbers run continuously across them and are the ones the rest of the documentation cites.

• From images to spots (§0–§3) — device-side decoding, geometry and reciprocal-space mapping, azimuthal integration, spot finding.
• Indexing and geometry refinement (§4–§7) — FFT and fast-feedback indexing, the lattice search, geometry refinement, post-refinement and powder calibration.
• Prediction, integration, scaling and merging (§8–§12) — reflection prediction, profile-fitted integration, scaling, merging, mosaicity and the auxiliary statistics.
• Space group and validation (§13–§14) — the space-group search, twinning, the resolution cutoff, diffraction anisotropy, and model-based validation.

References

The methods draw on, and in places reimplement, solutions from:

• W. Kabsch, “XDS”, Acta Cryst. D66 (2010), 125–132 and related XDS papers (rotation geometry, partiality, scaling concepts).
• W. Kabsch, “Integration, scaling, space-group assignment and post-refinement”, Acta Cryst. D66 (2010), 133–144 (mosaicity/partiality likelihood treatment; notation such as ζ and rotation factors).
• T. A. White et al., CrystFEL method papers (spot finding, three‑ring integration, serial/still diffraction processing concepts).
• J. Kieffer & J. P. Wright, "PyFAI: a Python library for high performance azimuthal integration on GPU", Powder Diffraction 28 (2013), S339-S350 (detector geometry definition, azimuthal integration)
• I. Steller, R. Bolotovsky & M. G. Rossmann, "An algorithm for automatic indexing of oscillation images using Fourier analysis", J. Appl. Cryst. 30 (1997), 1036-1040 (the projection/1D-FFT autoindexing algorithm of §5).
• H. Powell, "The Rossmann Fourier autoindexing algorithm in MOSFLM", Acta Cryst. D55 (1999), 1690-1695 (the MOSFLM implementation of it, whose practice is followed)
• P. Gasparotto, L. Barba, H.-C. Stadler et al., "TORO Indexer: a PyTorch-based indexing algorithm for kilohertz serial crystallography", J. Appl. Cryst. 57 (2024), 931-944 (the algorithm of the ffbidx fast-feedback indexer, §4).
• I. Křivý & B. Gruber, "A unified algorithm for determining the reduced (Niggli) cell", Acta Cryst. A32 (1976), 297-298, and International Tables for Crystallography Vol. A, Table 9.2.5.1 (the Niggli reduction and the lattice-character table of §5.3/§6).
• J. E. Padilla & T. O. Yeates, "A statistic for local intensity differences: robustness to anisotropy and pseudo-centering and utility for detecting twinning", Acta Cryst. D59 (2003), 1124-1130 (the L test, §13.2).
• A. Barty, R. A. Kirian, F. R. N. C. Maia et al., "Cheetah: software for high-throughput reduction and analysis of serial femtosecond X-ray diffraction data", J. Appl. Cryst. 47 (2014), 1118-1131 (peakfinder8: the per-resolution-ring background statistics of §3.2).
• A. Hennequin, B. Couturier, V. V. Gligorov & L. Lacassagne, "SparseCCL: Connected Components Labeling and Analysis for sparse images", DASIP 2019, 65-70 (the connected-component labelling of §3.4, used via ACTS/traccc).
• S. French & K. Wilson, "On the treatment of negative intensity observations", Acta Cryst. A34 (1978), 517-525 (Bayesian amplitude estimation from intensities).
• A. T. Brünger, "Free R value: a novel statistical quantity for assessing the accuracy of crystal structures", Nature 355 (1992), 472-475 (R-free cross-validation).
• M. Wojdyr, "GEMMI: A library for structural biology", J. Open Source Softw. 7 (2022), 4200 (model / structure-factor / map machinery used in §14).
• J. P. Wright, "Experiences with GPU decompression for bitshuffle + LZ4 data", HDF5 User Group meeting (2021), and github.com/jonwright/bslz4decoders (device-side decoding of bitshuffle+LZ4 images, §0).
• A. Thorn & G. M. Sheldrick, "ANODE: anomalous and heavy-atom density calculation", J. Appl. Cryst. 44 (2011), 1285-1287 (anomalous difference density read at the model's sites).
• Z. Otwinowski & W. Minor, "Processing of X-ray diffraction data collected in oscillation mode", Methods Enzymol. 276 (1997), 307-326 (reweighted, de-biased profile-fit variances).
• G. Winter et al., "DIALS: implementation and evaluation of a new integration package", Acta Cryst. D74 (2018), 85-97, and J. Beilsten-Edmands et al., Acta Cryst. D76 (2020), 385-399 (CC1/2 resolution cutoff, merge outlier rejection, scaling error model).
• P. Evans, "Scaling and assessment of data quality", Acta Cryst. D62 (2006), 72-82, and P. R. Evans, Acta Cryst. D67 (2011), 282-292 (POINTLESS: operator-by-operator point-group scoring, and the axial-zone screw-absence test).
• A. G. W. Leslie & H. R. Powell, "Processing diffraction data with MOSFLM" (2007), NATO Science Series II 245, 41-51 (post-refinement practice: what is refined per image and what over a wedge).
• D. W. Moreau, H. Atakisi & R. E. Thorne, "Ice in biomolecular cryocrystallography", Acta Cryst. D77 (2021), 540-554 (measured hexagonal-ice ring positions, used by the ice-ring score, the ice flagging and the ice calibrant).
• K. Röttger, A. Endriss, J. Ihringer, S. Doyle & W. F. Kuhs, "Lattice constants and thermal expansion of H2O and D2O ice Ih between 10 and 265 K", Acta Cryst. B50 (1994), 644-648 (the ice Ih cell the ring positions below 1.522 Å are calculated from).
• S. Sheriff & W. A. Hendrickson, "Description of overall anisotropy in diffraction from macromolecular crystals", Acta Cryst. A43 (1987), 118-121 (the overall anisotropic B tensor and its symmetry constraints), and A. N. Popov & G. P. Bourenkov, "Choice of data-collection parameters based on statistic modelling", Acta Cryst. D59 (2003), 1145-1153 (the sigma-aware estimation of the anisotropy of the observed intensity distribution, part of that paper's statistic modelling).
• P. R. Evans & G. N. Murshudov, "How good are my data and what is the resolution?", Acta Cryst. D69 (2013), 1204-1214 (AIMLESS: the anisotropic deltaB as the range of the principal components, and diffraction limits from a cone about each principal direction).
• K. Diederichs & P. A. Karplus, Nat. Struct. Biol. 4 (1997), 269-275, and P. A. Karplus & K. Diederichs, Science 336 (2012), 1030-1033 (R_meas / R_pim, CC1/2 and CC*).
• IUCr Commission on Crystallographic Nomenclature, "Statistical descriptors in crystallography", Acta Cryst. A45 (1989), 63-75, and Acta Cryst. A51 (1995), 565-569 (uncertainty conventions).

(list is not exhaustive; the full citations, with DOIs, are in ACKNOWLEDGEMENT.md)