AL-837: Compute resample output WCS from known s_region instead of re…

…calculating footprints (#8893)

changes/8893.resample.rst

@@ -0,0 +1 @@
+Use s_region list to calculate output footprint instead of re-computing via WCS transforms

jwst/assign_mtwcs/moving_target_wcs.py

@@ -18,6 +18,8 @@
 
 from jwst.datamodels import ModelLibrary
 from jwst.stpipe.utilities import record_step_status
+from jwst.assign_wcs.util import update_s_region_imaging
+from jwst.lib.exposure_types import IMAGING_TYPES
 
 log = logging.getLogger(__name__)
 log.setLevel(logging.DEBUG)
@@ -69,6 +71,8 @@ def assign_moving_target_wcs(input_models):
                                     model.meta.wcsinfo.mt_ra, model.meta.wcsinfo.mt_dec)
                 del model.meta.wcs
                 model.meta.wcs = new_wcs
+            if model.meta.exposure.type.lower() in IMAGING_TYPES:
+                update_s_region_imaging(model)
             record_step_status(model, "assign_mtwcs", True)
             input_models.shelve(model, i, modify=True)
 

jwst/outlier_detection/tests/test_outlier_detection.py

@@ -6,6 +6,7 @@
 
 from gwcs.wcs import WCS
 from stdatamodels.jwst import datamodels
+from stcal.alignment.util import compute_s_region_imaging
 
 from jwst.datamodels import ModelContainer, ModelLibrary
 from jwst.assign_wcs import AssignWcsStep
@@ -151,6 +152,7 @@ def we_many_sci(
 
     # Replace the FITS-type WCS with an Identity WCS
     sci1.meta.wcs = create_fitswcs(sci1)
+    sci1.meta.wcsinfo.s_region = compute_s_region_imaging(sci1.meta.wcs, shape=shape, center=False)
     rng = np.random.default_rng(720)
     sci1.data = rng.normal(loc=background, size=shape, scale=sigma)
     sci1.err = np.zeros(shape) + sigma

jwst/resample/resample_utils.py

@@ -28,9 +28,15 @@ def make_output_wcs(input_models, ref_wcs=None,
     Parameters
     ----------
     input_models : `~jwst.datamodel.ModelLibrary`
-        Each datamodel must have a ~gwcs.WCS object.
+        The datamodels to combine into a single output WCS. Each datamodel must
+        have a ``meta.wcs.s_region`` attribute.
 
-    pscale_ratio : float, optional
+    ref_wcs : gwcs.WCS, None, optional
+        Custom WCS to use as the output WCS. If not provided,
+        the reference WCS will be taken as the WCS of the first input model, with
+        its bounding box adjusted to encompass all input frames.
+
+    pscale_ratio : float, None, optional
         Ratio of input to output pixel scale. Ignored when ``pscale``
         is provided.
 
@@ -67,27 +73,26 @@ def make_output_wcs(input_models, ref_wcs=None,
         WCS object, with defined domain, covering entire set of input frames
     """
     if ref_wcs is None:
+        sregion_list = []
         with input_models:
-            wcslist = []
             for i, model in enumerate(input_models):
-                w = model.meta.wcs
-                if w.bounding_box is None:
-                    w.bounding_box = wcs_bbox_from_shape(model.data.shape)
-                wcslist.append(w)
+                sregion_list.append(model.meta.wcsinfo.s_region)
                 if i == 0:
                     example_model = model
+                    ref_wcs = example_model.meta.wcs
+                    ref_wcsinfo = example_model.meta.wcsinfo.instance
                 input_models.shelve(model)
-        naxes = wcslist[0].output_frame.naxes
+        naxes = ref_wcs.output_frame.naxes
 
         if naxes != 2:
             msg = ("Output WCS needs 2 spatial axes "
                    f"but the supplied WCS has {naxes} axes.")
             raise RuntimeError(msg)
 
-        output_wcs = util.wcs_from_footprints(
-            wcslist,
-            ref_wcs=wcslist[0],
-            ref_wcsinfo=example_model.meta.wcsinfo.instance,
+        output_wcs = util.wcs_from_sregions(
+            sregion_list,
+            ref_wcs,
+            ref_wcsinfo,
             pscale_ratio=pscale_ratio,
             pscale=pscale,
             rotation=rotation,