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leonarski_fandClaude Opus 5 a72ba82f48 Powder calibration: write rot2/rot3 in pyFAI's frame, not ours
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The .poni file carried rot2 and rot3 with our sign, which is not pyFAI's. pyFAI
has the slow axis increasing bottom to top; the MX convention runs top to bottom,
so the two frames differ by a reflection in y. Conjugating a rotation by a
reflection gives R(n, theta) -> R(Mn, -theta), so for rot2 (about x) and rot3
(about the beam) the sense reverses, while for rot1 the axis IS y and the axis and
the sense reverse together and cancel. Negate the first two, leave rot1 alone.

Poni1/Poni2 are unaffected: they are distances from pixel (0, 0) along each axis,
which the direction the axis runs in does not change.

Caught by integrating a LaB6 image in pyFAI with the file we had just written.
Unflipped, the rings come out BROADER than they do with no tilt at all - peak
height 42 against 30, mean ring-position error 0.0045 1/A against 0.0027 - which
is the signature of a tilt applied the wrong way. Flipped, they sharpen to 132 and
0.0005, and flipping rot1 as well makes it far worse (peak 5), so the asymmetry is
real and not a fitting artefact.

The unit test pinned the old signs, so it passed throughout. It now pins the
verified ones and says why, since the stored values and the written ones
disagreeing looks like a bug unless the reason is written down.

Only the exported file was wrong. Nothing internal changes: the fitted geometry
and everything downstream of it in Jungfraujoch were always self-consistent.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-07 12:04:41 +02:00
leonarski_fandClaude Opus 5 6468dd13be rugnux: --mode, and detector calibration from powder rings
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--azint-only and --scale are replaced by --mode mx|azint|scale|calibration, with
mx the default. The old flags are removed rather than aliased.

Calibration mode fits the detector geometry - PONI x/y, the two tilts and the
distance - to a calibrant's powder rings and writes a pyFAI .poni alongside a
report of how far each parameter moved from the header. Bragg data constrain the
beam centre worst, because it is gauge-coupled to the crystal orientation; a
powder ring has no orientation to couple to.

--calibrant takes lab6, agbh, ceo2, si or ice. A calibrant is a list of ring
positions rather than a unit cell, because hexagonal ice is P6_3/mmc: rings
enumerated from its cell would include systematically absent ones. So the
crystalline standards generate their rings from a cell and ice carries the
measured list, and RingsFromAzimuthalProfile, GuessGeometry and OptimizeGeometry
all take ring q. The calibrant table is shared with the viewer's powder panel,
which previously carried its own copy.

--calibration picks how the rings are measured: rings (default) sums the
(q x azimuth) profile over every processed image and fits the arcs in it; spots
pools the found spots and fits those. Both use the whole run, with -s/-e/-t
selecting images. rings defaults --azim-phi-bins to 32, since a profile with one
azimuthal bin has averaged the ring over every direction and cannot locate it.

Two fixes this exposed:

The extraction window is capped at half the gap to the neighbouring ring. The
background under a peak is taken from the ends of its window, so a window wider
than half that gap measures the next ring's flank as this ring's background -
and hexagonal ice has three rings within 0.06 1/A. Ice calibration was 3.5 px
out before this and 0.29 px after; LaB6 is unaffected.

RingOptimizer holds rot1/rot2 fixed when only one ring is present. A tilt and a
centre offset both move a ring as cos(phi) and are separated only by the tilt's
amplitude growing as the ring radius squared, so on a single ring they are
exactly degenerate.

Measured. LaB6 at five distances: the fitted direct beam is within 0.36 px of an
independent implementation out to 300 mm, and D = -0.046 + 1.000788 dtz with an
rms of 0.011 mm. At 500 mm one ring is fully on the detector and a second only
clips the corners, which is not enough to constrain a tilt - restricting the q
range to the resolved ring recovers 0.06 px. Ice: 5.53 -> 0.29 px on one crystal
and 4.71 -> 0.80 px on another, against XDS's refined direct beam. On an ice-free
crystal the fit is worse than the header, which is the correct outcome.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2026-08-07 10:00:03 +02:00