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HLA-1610: Scale missing from idctab bug #249

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HLA-1610: Scale missing from idctab bug #249

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45634f0
initial commit.
s-goldman Jul 8, 2026
47bd352
added changelog.
s-goldman Jul 8, 2026
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11 changes: 11 additions & 0 deletions CHANGES.rst
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Original file line number Diff line number Diff line change
@@ -1,3 +1,14 @@
===================
STWCS Release Notes
===================


1.7.8 (TBD)
-----------

- Bug fix for empty scale value returned from idctab [#249]


1.7.7 (2026-03-05)
------------------

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4 changes: 4 additions & 0 deletions stwcs/distortion/utils.py
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Expand Up @@ -111,12 +111,16 @@ def make_orthogonal_cd(wcs):
pv += wcs.idctheta
cs = np.cos(np.deg2rad(pv))
sn = np.sin(np.deg2rad(pv))

pvmat = np.dot(np.array([[cs, sn], [-sn, cs]]), wcs.parity)
rot = np.arctan2(pvmat[0, 1], pvmat[1, 1])

det = linalg.det(wcs.parity)
if hasattr(wcs, 'idcscale') and wcs.idcscale is not None:
scale = (wcs.idcscale) / 3600. # HST pixel scale provided
else:
warnings.warn("IDCSCALE is missing, computing it from CD matrix.")
scale = np.sqrt(np.abs(det)) # find as sqrt(pixel area)
else:

det = linalg.det(cd)
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