Fix msa frame transform for opaque images (#9102)

changes/9102.assign_wcs.rst

@@ -0,0 +1 @@
+Fix crash in transform from MSA to detector coordinates for NIRSpec imaging WCS with filter=OPAQUE.

jwst/assign_wcs/nirspec.py

@@ -108,6 +108,10 @@ def imaging(input_model, reference_files):
 
     lam = wrange[0] + (wrange[1] - wrange[0]) * .5
 
+    # Scale wavelengths to microns if msa coordinates are terminal
+    if input_model.meta.instrument.filter == 'OPAQUE':
+        lam *= 1e6
+
     lam_model = Mapping((0, 1, 1)) | Identity(2) & Const1D(lam)
 
     gwa2msa = gwa_through | rotation | dircos2unitless | col | lam_model
@@ -148,8 +152,7 @@ def imaging(input_model, reference_files):
                             (v2v3vacorr, tel2sky),
                             (world, None)]
     else:
-        # convert to microns if the pipeline ends earlier
-        gwa2msa = (gwa2msa | Identity(2) & Scale(1e6)).rename('gwa2msa')
+        # Pipeline ends with MSA coordinates
         imaging_pipeline = [(det, dms2detector),
                             (sca, det2gwa),
                             (gwa, gwa2msa),

jwst/assign_wcs/tests/test_nirspec.py

@@ -91,11 +91,13 @@ def create_reference_files(datamodel):
     return refs
 
 
-def create_nirspec_imaging_file():
+def create_nirspec_imaging_file(filter_name='F290LP'):
     image = create_hdul()
     image[0].header['exp_type'] = 'NRS_IMAGE'
-    image[0].header['filter'] = 'F290LP'
+    image[0].header['filter'] = filter_name
     image[0].header['grating'] = 'MIRROR'
+    image[0].header['lamp'] = 'NONE'
+
     return image
 
 
@@ -162,6 +164,39 @@ def test_nirspec_imaging():
     # Test evaluating the WCS
     im.meta.wcs(1, 2)
 
+    # Test that the MSA to detector transforms can be retrieved
+    det2msa = im.meta.wcs.get_transform('detector', 'msa')
+    result = det2msa(1.0, 2.0)
+    assert len(result) == 3
+
+    msa2det = im.meta.wcs.get_transform('msa', 'detector')
+    result = msa2det(1.0, 2.0)
+    assert len(result) == 2
+
+
+def test_nirspec_imaging_opaque():
+    """Test NIRSpec Imaging mode with OPAQUE filter."""
+    f = create_nirspec_imaging_file(filter_name='OPAQUE')
+    im = datamodels.ImageModel(f)
+
+    # Test creating the WCS
+    refs = create_reference_files(im)
+    pipe = nirspec.create_pipeline(im, refs, slit_y_range=[-.5, .5])
+    w = wcs.WCS(pipe)
+    im.meta.wcs = w
+
+    # Test evaluating the WCS
+    im.meta.wcs(1, 2)
+
+    # Test that the MSA to detector transforms can be retrieved
+    det2msa = im.meta.wcs.get_transform('detector', 'msa')
+    result = det2msa(1.0, 2.0)
+    assert len(result) == 3
+
+    msa2det = im.meta.wcs.get_transform('msa', 'detector')
+    result = msa2det(1.0, 2.0)
+    assert len(result) == 2
+
 
 def test_nirspec_ifu_against_esa(wcs_ifu_grating):
     """