Geometry is re-refined independently on every frame, against that frame's spots
alone - as few as a dozen on a sparse crystal, where XDS fits its equivalent to
about sixty times more data. Measured over ten datasets the per-frame orientation
carries two components: a slow drift that is real, with rugnux and XDS agreeing to
R^2 0.83-0.88 on the two crystals that genuinely slip by 1.5 and 0.54 degrees, and
a fast jitter that is fit noise, scaling with spots-per-frame at exponent -0.79
where counting noise alone would give -0.5. The jitter is worth 1-8% on merged
intensities, 24% on the sparsest crystal.
It cannot be fixed by refining less. Turning per-image refinement off entirely
loses six space groups and a whole crystal, and even a 624-spot-per-frame crystal
collapses; dropping the beam-centre terms holds the space groups but is worse on
31 of 37 crystals. The freedom is earning its keep, so keep it and suppress only
the band that cannot be physical - a crystal does not re-orient and snap back from
one frame to the next.
So smooth the orientation in frame order after integration and recompute each
partial's delta_phi, and hence its partiality, from the smoothed lattice. Batching
at integration time was not an option: frames are processed independently and the
online path depends on that. This runs before the GPU upload, so the device path
picks it up with no separate kernel.
The window is chosen per dataset by leave-one-out cross-validation, because the
two components vary far too much for one number - drift spans 0.018 to 1.288
degrees and jitter 0.005 to 0.221, so any fixed window over-smooths one crystal
while under-smoothing another. Chosen windows range from +-1 to +-20 frames. It is
capped: cross-validation scores how well neighbours predict a frame's orientation,
which on a barely-drifting crystal keeps improving with width, but the per-frame
fit is also absorbing a real per-frame systematic and smoothing too wide destroys
it - uncapped, one crystal chose +-60 and lost 16% of its ISa.
Battery over 37 crystals: space groups unchanged at 34 matching XDS, R_meas better
on 31 and worse on 6, low-resolution R_meas 30/7, ISa 26/10, high-resolution CC1/2
23/12.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
017f64690c
