FA-55018 / Astronomical coordinate conventions / Member archive
Linear spectral pixel calibration: Reference-shifted spectral curvature omits the cubic binomial coefficient · case 03
The adapter reports an incorrect shifted quadratic while other fields remain valid.
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 fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| astronomical fixture 0 | {"absolute_constant": 94, "coordinate": 436, "local_dispersion": 146, "shifted_linear": 26, "shifted_quadratic": 3, "shifted_zero": 124} | {"absolute_constant": 94, "coordinate": 436, "local_dispersion": 146, "shifted_linear": 26, "shifted_quadratic": 9, "shifted_zero": 124} | Failed |
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