FA-56262 / Astronomical coordinate conventions / Member archive
Wcs cube storage order: WCS reference pixel tuple uses a different axis convention from the stored cube · case 02
The adapter reports an incorrect storage reference while other fields remain valid.
Case contract
A FITS-like cube uses pixel order x,y,spectral z but a Python array stores z,y,x. Shape is nz,ny,nx, one-based WCS reference pixels rx,ry,rz. Reference tuple and linear CD input columns must honor this permutation; CD output rows and CTYPE world labels retain world-axis order. No celestial projection is evaluated. Output fields are defined by: array_index = [d['z']-1,d['y']-1,d['x']-1]; fits_shape = [d['nx'],d['ny'],d['nz']]; storage_reference = [d['rz']-1,d['ry']-1,d['rx']-1]; storage_cd = [list(reversed(row)) for row in d['cd']]; world_axis_types = d['ctype']; world_delta = [d['x']-d['rx'],d['y']-d['ry'],d['z']-d['rz']]
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 | {"array_index": [1, 4, 3], "fits_shape": [20, 30, 8], "storage_cd": [[3, 2, 1], [6, 5, 4], [10, 8, 7]], "storage_reference": [9, 14, 3], "world_axis_types": ["RA---TAN", "DEC--TAN", "FREQ"], "world_delta": [-6, -10, -2]} | {"array_index": [1, 4, 3], "fits_shape": [20, 30, 8], "storage_cd": [[3, 2, 1], [6, 5, 4], [10, 8, 7]], "storage_reference": [3, 14, 9], "world_axis_types": ["RA---TAN", "DEC--TAN", "FREQ"], "world_delta": [-6, -10, -2]} | Failed |
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