Wrap average RA to 0-360

Author: melanieclarke

changes/10456.cube_build.rst

@@ -0,0 +1 @@
+Wrap average RA values to the 0-360 degree range, to fix negative CRVAL1 values in output cubes.

jwst/cube_build/ifu_cube.py

@@ -340,7 +340,7 @@ def set_geometry(self, corner_a, corner_b, lambda_min, lambda_max):
 
         # astropy circmean assumes angles are in radians,
         # we have angles in degrees
-        ra_ave = circmean(ravalues * u.deg).value
+        ra_ave = circmean(ravalues * u.deg).value % 360
 
         if self.ra_center is not None:
             self.crval1 = self.ra_center

jwst/cube_build/tests/test_cube_build_step.py

@@ -7,6 +7,7 @@
 import numpy as np
 import pytest
 from astropy.io import fits
+from astropy.modeling.models import Identity, Shift
 from stdatamodels.jwst.datamodels import IFUImageModel
 
 from jwst.adaptive_trace_model import AdaptiveTraceModelStep
@@ -271,3 +272,22 @@ def test_cube_build_oversampled(request, oversample, dataset, output_shape):
 
     # Input data is flat, so output data should have the same mean value
     np.testing.assert_allclose(np.nanmean(cube.data), np.nanmean(model.data))
+
+
+@pytest.mark.parametrize("shift_ra", [True, False])
+def test_output_crval1_positive(miri_data, shift_ra):
+    model = miri_data.copy()
+
+    expected_ra = 164
+    if shift_ra:
+        # Shift RA by 100 degrees to make it > 180
+        model.meta.wcs.pipeline[-2].transform |= Shift(100) & Identity(2)
+        model.meta.wcsinfo.ra_ref += 100
+        model.meta.wcsinfo.s_region = model.meta.wcsinfo.s_region.replace("164", "264")
+        expected_ra += 100
+
+    result = CubeBuildStep.call(model)
+
+    # Output RA should be between 0 and 360
+    for cube in result:
+        assert np.isclose(cube.meta.wcsinfo.crval1, expected_ra, atol=1)