FA-55245 / Astronomical coordinate conventions / Member archive

Catalog error ellipse: Quarter-turn astrometric covariance omits the cross-term sign change · case 05

The adapter reports an incorrect rotated covariance while other fields remain valid.

Member previewVariant 5 · 3 implementations · 6 checks per implementation

Case contract

A tangent-plane catalog covariance has variances a,b and covariance c. Axis scale sx,sy includes signed orientation. A 90-degree basis rotation maps (x,y) to (-y,x). A projected RA coordinate supplied factor q converts covariance using a diagonal Jacobian. No confidence-level conversion is implied. Output fields are defined by: scaled_variance_x = d['a']*d['sx']**2; scaled_covariance = d['c']*d['sx']*d['sy']; rotated_covariance = -d['c']; projected_variance = d['a']*d['q']**2; projected_cross_term = d['c']*d['q']; determinant = d['a']*d['b']-d['c']**2

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	`{"determinant": 199, "projected_cross_term": 6, "projected_variance": 52, "rotated_covariance": 3, "scaled_covariance": -18, "scaled_variance_x": 52}`	`{"determinant": 199, "projected_cross_term": 6, "projected_variance": 52, "rotated_covariance": -3, "scaled_covariance": -18, "scaled_variance_x": 52}`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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