HLA-1587: Ignore distortion header keywords when comparing test WCS solutions

CHANGES.rst

@@ -1,3 +1,10 @@
+1.7.8 (TBD)
+-----------
+
+- Bug fix addressing astropy wcs change enabling secondary distortion correction 
+  keywords. [#246]
+
+
 1.7.7 (2026-03-05)
 ------------------
 

stwcs/tests/test_headerlet.py

@@ -240,18 +240,26 @@ def test_apply_as_primary_method(self):
     @pytest.mark.skipif(os.name == "nt", reason="FIXME: Crash on Windows")
     def test_apply_as_alternate_method(self):
         hlet = headerlet.create_headerlet(self.comp_file, hdrname='test1')
+
+        # Make the headerlet WCS distinct from the current primary WCS
+        hlet['SIPWCS', 1].header['CRPIX1'] += 1
+        hlet['SIPWCS', 1].header['CRPIX2'] += 1
+        hlet['SIPWCS', 2].header['CRPIX1'] += 2
+        hlet['SIPWCS', 2].header['CRPIX2'] += 2
+
         hlet.apply_as_alternate(self.comp_file, wcskey='K', wcsname='KK')
+        assert fits.getval(self.comp_file, 'WCSNAMEK', ext=('SCI', 1)) == 'KK'
         hlet.writeto(self.headerlet_name, overwrite=True)
         assert(wcsdiff.is_wcs_identical(self.comp_file, self.headerlet_name,
                                         [('SCI', 1), ('SCI', 2)],
                                         [("SIPWCS", 1), ("SIPWCS", 2)],
-                                        scikey='K', verbose=True)[0])
+                                        scikey='K', verbose=True, ignore_cpdis=True)[0])
         headerlet.apply_headerlet_as_alternate(self.comp_file,
                                                self.headerlet_name, wcskey='P')
         assert(wcsdiff.is_wcs_identical(self.comp_file, self.headerlet_name,
                                         [('SCI', 1), ('SCI', 2)],
                                         [("SIPWCS", 1), ("SIPWCS", 2)],
-                                        scikey='P', verbose=True)[0])
+                                        scikey='P', verbose=True, ignore_cpdis=True)[0])
 
 class TestRestoreHeaderlet:
 

stwcs/wcsutil/wcsdiff.py

@@ -6,7 +6,7 @@
 
 
 def is_wcs_identical(scifile, file2, sciextlist, fextlist, scikey=" ",
-                     file2key=" ", verbose=False):
+                     file2key=" ", ignore_cpdis=False, verbose=False):
     """
     Compares the WCS solution of 2 files.
 
@@ -26,6 +26,8 @@ def is_wcs_identical(scifile, file2, sciextlist, fextlist, scikey=" ",
              alternate WCS key in scifile
     file2key: string
              alternate WCS key in file2
+    ignore_cpdis: bool
+             True: ignore CPDIS1 and CPDIS2 when comparing WCS solutions
     verbose: bool
              True: print to stdout
 
@@ -83,21 +85,24 @@ def is_wcs_identical(scifile, file2, sciextlist, fextlist, scikey=" ",
                 # logger.info('SIP coefficients do not match')
                 diff['SIP_B'] = (w1.sip.b, w2.sip.b)
                 result = False
-        if w1.cpdis1 or w2.cpdis1:
-            if w1.cpdis1 and not w2.cpdis1 or w2.cpdis1 and not w1.cpdis1:
-                diff['CPDIS1'] = "CPDIS1 missing"
-                result = False
-            if w1.cpdis2 and not w2.cpdis2 or w2.cpdis2 and not w1.cpdis2:
-                diff['CPDIS2'] = "CPDIS2 missing"
-                result = False
-            if not np.allclose(w1.cpdis1.data, w2.cpdis1.data, rtol=10**(-7)):
-                # logger.info('NPOL distortions do not match')
-                diff['CPDIS1_data'] = (w1.cpdis1.data, w2.cpdis1.data)
-                result = False
-            if not np.allclose(w1.cpdis2.data, w2.cpdis2.data, rtol=10**(-7)):
-                # logger.info('NPOL distortions do not match')
-                diff['CPDIS2_data'] = (w1.cpdis2.data, w2.cpdis2.data)
-                result = False
+        if ignore_cpdis:
+            pass
+        else:
+            if w1.cpdis1 or w2.cpdis1:
+                if w1.cpdis1 and not w2.cpdis1 or w2.cpdis1 and not w1.cpdis1:
+                    diff['CPDIS1'] = "CPDIS1 missing"
+                    result = False
+                if w1.cpdis2 and not w2.cpdis2 or w2.cpdis2 and not w1.cpdis2:
+                    diff['CPDIS2'] = "CPDIS2 missing"
+                    result = False
+                if not np.allclose(w1.cpdis1.data, w2.cpdis1.data, rtol=10**(-7)):
+                    # logger.info('NPOL distortions do not match')
+                    diff['CPDIS1_data'] = (w1.cpdis1.data, w2.cpdis1.data)
+                    result = False
+                if not np.allclose(w1.cpdis2.data, w2.cpdis2.data, rtol=10**(-7)):
+                    # logger.info('NPOL distortions do not match')
+                    diff['CPDIS2_data'] = (w1.cpdis2.data, w2.cpdis2.data)
+                    result = False
         if w1.det2im1 or w2.det2im1:
             if w1.det2im1 and not w2.det2im1 or \
                     w2.det2im1 and not w1.det2im1: