[us-commits] [ehb54/ultrascan3] 6274fe: somo/grpy: raise the exposure quadrature to 512 po...

[emre brookes]

  Branch: refs/heads/ehb54-984-quadrature
  Home:   https://github.com/ehb54/ultrascan3
  Commit: 6274fe15b2945427c5b165214cc1ac603a418673
      https://github.com/ehb54/ultrascan3/commit/6274fe15b2945427c5b165214cc1ac603a418673
  Author: Emre Brookes <emre.brookes at umontana.edu>
  Date:   2026-08-17 (Mon, 17 Aug 2026)

  Changed paths:
    M us_somo/develop/grpy/grpy_exposure.hpp
    M us_somo/develop/grpy/grpy_shell.hpp

  Log Message:
  -----------
  somo/grpy: raise the exposure quadrature to 512 points per bead

The exposure point pattern is generated once in the coordinate frame and applied to
every bead by translation and scaling, so it does not rotate with the structure. A
rigid rotation therefore changes 34-77% of bead exposures by a few of the K sample
points and changes the ranking. A translation-only control is completely inert and
the unreduced result is invariant to zero parts per million, so this is the
quadrature, not arithmetic.

The effect reaches the answer almost entirely through the stopping decision, not
through which beads are kept: where the ladder stops at the same rung in every frame
the reported value moves by at most 0.075%, and where the orientation flips the rung
by one it moves by up to 1.043% -- a ratio of roughly fourteen, replicated on two
independent grids.

Measured over twelve rigid motions of six models, matched but for K: at 64, one case
of eighteen changed its stopping rung and the frame-to-frame spread reached 0.23%; at
512, no case changes rung and the spread falls to 0.016%. Retained beads are unchanged
(mean 31.5% vs 31.3%), and compliance and coverage are perfect at both values, so the
finer quadrature costs only exposure time -- about 3% of the ladder, exposure being
milliseconds against a solve of seconds.

This does not make selection frame-independent; subsets still differ in nearly every
frame. It makes the delivered result about 14x less sensitive to orientation, which is
what matters to a user who reorients their coordinates and reruns.

The low-level exposure() default stays 64 and is now annotated as such: every
production caller passes K explicitly, and the shipped value is ShellOptions::K.

This changes which beads are selected, so all frozen validation figures must be
regenerated and the freeze tag moved.

Fixes ehb54/ultrascan-tickets#984

Co-Authored-By: Claude Opus 5 <noreply at anthropic.com>



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