FA-12178 / Astronomical coordinate conventions / Member archive

A FITS CD matrix receives the CDELT axis scale a second time · case 03

A FITS CD matrix receives the CDELT axis scale a second time.

Member previewVariant 3 · 3 implementations · 6 checks per implementation

Case contract

Reduced two-axis linear FITS WCS model: delta is pixel offset, matrix is CD or PC according to mode. CD maps directly; PC requires output-row scaling by scale. Return two intermediate world coordinates, before sky projection.

Why this case matters

Astronomical coordinate adapters must preserve convention semantics. Primary background: https://docs.astropy.org/en/stable/api/astropy.wcs.Wcsprm.html

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
CD includes scale	`[40, 63]`	`[8, 9]`	Failed

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