Fix bug in _xyz_to_lonlat_rad

test/grid/grid/test_io.py

@@ -174,3 +174,26 @@ def test_grid_ugrid_exodus_roundtrip(gridpath):
     for filepath in test_files:
         if os.path.exists(filepath):
             os.remove(filepath)
+
+
+def test_exodus_roundtrip_rll1deg_node_lonlat(gridpath, tmp_path):
+    """Check Exodus round-trip coordinate stability for the RLL1deg grid."""
+    grid = ux.open_grid(gridpath("ugrid", "outRLL1deg", "outRLL1deg.ug"))
+
+    exodus_filepath = tmp_path / "outRLL1deg.exo"
+    grid.to_xarray("Exodus").to_netcdf(exodus_filepath)
+
+    reloaded_exodus = ux.open_grid(exodus_filepath)
+
+    np.testing.assert_allclose(
+        grid.node_lon.values,
+        reloaded_exodus.node_lon.values,
+        err_msg="Exodus longitude mismatch for RLL1deg",
+        rtol=ERROR_TOLERANCE,
+    )
+    np.testing.assert_allclose(
+        grid.node_lat.values,
+        reloaded_exodus.node_lat.values,
+        err_msg="Exodus latitude mismatch for RLL1deg",
+        rtol=ERROR_TOLERANCE,
+    )

uxarray/grid/coordinates.py

@@ -68,10 +68,10 @@ def _xyz_to_lonlat_rad_no_norm(
 def _xyz_to_lonlat_rad_scalar(x, y, z, normalize=True):
     if normalize:
         x, y, z = _normalize_xyz_scalar(x, y, z)
-        denom = abs(x * x + y * y + z * z)
-        x /= denom
-        y /= denom
-        z /= denom
+        denom = math.hypot(math.hypot(x, y), z)
+        x = x / denom
+        y = y / denom
+        z = z / denom
 
     lon = np.arctan2(y, x)
     lat = np.asin(z)
@@ -121,10 +121,10 @@ def _xyz_to_lonlat_rad(
 
     if normalize:
         x, y, z = _normalize_xyz(x, y, z)
-        denom = np.abs(x * x + y * y + z * z)
-        x /= denom
-        y /= denom
-        z /= denom
+        denom = np.hypot(np.hypot(x, y), z)
+        x = x / denom
+        y = y / denom
+        z = z / denom
 
     lon = np.arctan2(y, x)
     lat = np.arcsin(z)