FA-55014 / Astronomical coordinate conventions / Member archive

Linear spectral pixel calibration: Reference-shifted spectral slope loses curvature from the cubic term · case 04

The adapter reports an incorrect shifted linear while other fields remain valid.

Member previewVariant 4 · 3 implementations · 6 checks per implementation

Case contract

Spectral coordinate is a reference-centered cubic in one-based pixel displacement t=p-r. Report coordinate, local derivative, reference-independent absolute constant, and the three coefficients after a shift of reference by s. This is a finite exact calibration polynomial, not a dispersion solution. Output fields are defined by: coordinate = d['a']+d['b']*(d['p']-d['r'])+d['c']*(d['p']-d['r'])**2+d['e']*(d['p']-d['r'])**3; local_dispersion = d['b']+2*d['c']*(d['p']-d['r'])+3*d['e']*(d['p']-d['r'])**2; absolute_constant = d['a']-d['b']*d['r']+d['c']*d['r']**2-d['e']*d['r']**3; shifted_zero = d['a']+d['b']*d['s']+d['c']*d['s']**2+d['e']*d['s']**3; shifted_linear = d['b']+2*d['c']*d['s']+3*d['e']*d['s']**2; shifted_quadratic = d['c']+3*d['e']*d['s']

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	`{"absolute_constant": 94, "coordinate": 604, "local_dispersion": 191, "shifted_linear": 2, "shifted_quadratic": 9, "shifted_zero": 124}`	`{"absolute_constant": 94, "coordinate": 604, "local_dispersion": 191, "shifted_linear": 26, "shifted_quadratic": 9, "shifted_zero": 124}`	Failed

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