FA-55829 / Astronomical coordinate conventions / Member archive

Slit sky coordinate: Along-slit nod is projected onto north with a detector-axis angle convention · case 04

The adapter reports an incorrect nod north while other fields remain valid.

Member previewVariant 4 · 3 implementations · 6 checks per implementation

Case contract

A spectrograph slit has supplied sine s and cosine c of position angle east of north. Sky offsets east E,north N map along slit E*s+N*c and across E*c-N*s. Slit scale a converts angle to detector pixels; spatial reference r and nod offset q are separate. Output fields are defined by: along_slit = d['E']*d['s']+d['N']*d['c']; across_slit = d['E']*d['c']-d['N']*d['s']; spatial_pixel = d['r']+(d['E']*d['s']+d['N']*d['c'])/d['a']; nodded_along = d['E']*d['s']+d['N']*d['c']-d['q']; nod_east = d['q']*d['s']; nod_north = d['q']*d['c']

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	`{"across_slit": 6, "along_slit": 5, "nod_east": 0, "nod_north": 0, "nodded_along": 1, "spatial_pixel": 12.5}`	`{"across_slit": 6, "along_slit": 5, "nod_east": 0, "nod_north": 4, "nodded_along": 1, "spatial_pixel": 12.5}`	Failed

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