do not error out with negative scales

pyproject.toml

@@ -25,8 +25,7 @@ dependencies = [
     # "rad >=0.19.2",
     # "roman_datamodels >=0.19.1",
     "rad @ git+https://github.com/spacetelescope/rad.git",
-    # "roman_datamodels @ git+https://github.com/spacetelescope/roman_datamodels.git",
-    "roman_datamodels @ git+https://github.com/stscieisenhamer/roman_datamodels.git@rcal-853-velocity",
+    "roman_datamodels @ git+https://github.com/spacetelescope/roman_datamodels.git",
     "gwcs >=0.19.0",
     "jsonschema >=4.8",
     "numpy >=1.22",

romanisim/tests/test_wcs.py

@@ -171,3 +171,25 @@ def test_scale_factor():
     sky = gwcs.pixel_to_world(grid, grid)
 
     assert all(truth.separation(sky).to(u.arcsec).value < 1e-3)
+
+
+def test_scale_factor_negative():
+    """Test that specifying a scale factor actually calculates a new wcs"""
+
+    # Truth aiming for.
+    cc = SkyCoord(ra=0 * u.deg, dec=0 * u.deg)
+    scale_factor = -99999
+    truth = SkyCoord([(0.        , 0.        ), (0.03055555, 0.03055555),
+                      (0.06111109, 0.06111105), (0.09166659, 0.09166647),
+                      (0.12222204, 0.12222176)],
+                     unit='deg')
+
+    # Make a simple grid of pixel coordinates to calculate sky for
+    grid = range(0, 4096, 1000)
+
+    # Create the wcs and generate results
+    distortion = make_fake_distortion_function()
+    gwcs = wcs.make_wcs(cc, distortion, scale_factor=scale_factor)
+    sky = gwcs.pixel_to_world(grid, grid)
+
+    assert all(truth.separation(sky).to(u.arcsec).value < 1e-3)

romanisim/wcs.py

@@ -34,6 +34,8 @@
 import romanisim.parameters
 import roman_datamodels.maker_utils as maker_utils
 
+from romanisim import log
+
 
 def fill_in_parameters(parameters, coord, pa_aper=0, boresight=True):
     """Add WCS info to parameters dictionary.
@@ -574,7 +576,9 @@ def dva_corr_model(va_scale, v2_ref, v3_ref):
         return models.Identity(2)
 
     if va_scale <= 0:
-        raise ValueError("'Velocity aberration scale must be a positive number.")
+        log.warning("Velocity aberration scale must be a positive number: %s", va_scale)
+        log.warning("Defaulting to scale of 1.0")
+        va_scale = 1.0
 
     va_corr = models.Scale(va_scale, name="dva_scale_v2") & models.Scale(
         va_scale, name="dva_scale_v3"