FA-12185 / Astronomical coordinate conventions / Member archive

SIP distortion is evaluated after the linear WCS transform · case 05

SIP distortion is evaluated after the linear WCS transform.

Member previewVariant 5 · 3 implementations · 6 checks per implementation

Case contract

Reduced SIP model for reference-relative pixel offsets u,v: corrected pair (u+a*u*u+b*u*v,v), followed by diagonal linear matrix (sx,sy). Return intermediate coordinates, no sky projection or full SIP implementation.

Why this case matters

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

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
square and cross distortion	`[360, 8]`	`[120, 8]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

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

Member access is invitation-based. Sign in with your invited account to inspect the sources.