FA-56192 / Astronomical coordinate conventions / Member archive

Spectrograph grating coordinate: Grating coordinate uses a different incidence-angle sign convention · case 02

The adapter reports an incorrect wavelength while other fields remain valid.

Member previewVariant 2 · 3 implementations · 6 checks per implementation

Case contract

A stipulated grating adapter supplies spacing g, signed sine of incidence a, signed sine of diffraction b, positive order m, focal length F, and separate calibration line wavelength line. Wavelength is g*(a+b)/m. A Littrow reference has b=a; supplied diffraction cosine c permits a local angular dispersion derivative. Output fields are defined by: wavelength = d['g']*(d['a']+d['b'])/d['m']; littrow_wavelength = 2*d['g']*d['a']/d['m']; angular_dispersion = d['g']*d['c']/d['m']; linear_dispersion = d['g']*d['c']/(d['m']*d['F']); inferred_diffraction_sine = d['m']*d['line']/d['g']-d['a']; next_order_wavelength = d['g']*(d['a']+d['b'])/(d['m']+1)

Why this case matters

Catalog, detector, sky-coordinate, and spectroscopy adapters must preserve the association between numeric coordinates and their declared reference conventions.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
astronomical fixture 0	`{"angular_dispersion": 20.166666666666668, "inferred_diffraction_sine": -0.25206611570247933, "linear_dispersion": 2.0166666666666666, "littrow_wavelength": 40.333333333333336, "next_order_wavelength": 22.6875, "wavelength": 10.083333333333334}`	`{"angular_dispersion": 20.166666666666668, "inferred_diffraction_sine": -0.25206611570247933, "linear_dispersion": 2.0166666666666666, "littrow_wavelength": 40.333333333333336, "next_order_wavelength": 22.6875, "wavelength": 30.25}`	Failed

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