Fix position noise ignoring unit of sigma

scipp · Feb 5, 2025 · f21e22b · f21e22b
1 parent e9473d8
commit f21e22b
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Showing 2 changed files with 15 additions and 1 deletion.
diff --git a/src/ess/reduce/live/raw.py b/src/ess/reduce/live/raw.py
@@ -528,9 +528,12 @@ def position_noise_for_cylindrical_pixel(
 
 
 def gaussian_position_noise(sigma: PositionNoiseSigma) -> PositionNoise:
+    sigma = sigma.to(unit='m', copy=False)
     size = _noise_size
     position = sc.empty(sizes={'position': size}, unit='m', dtype=sc.DType.vector3)
-    position.values = np.random.default_rng().normal(0, sigma.value, size=(size, 3))
+    position.values = np.random.default_rng(seed=1234).normal(
+        0, sigma.value, size=(size, 3)
+    )
     return PositionNoise(position)
 
 

diff --git a/tests/live/raw_test.py b/tests/live/raw_test.py
@@ -7,6 +7,17 @@
 from ess.reduce.live import raw
 
 
+@pytest.mark.parametrize(
+    'sigma',
+    [sc.scalar(0.01, unit='m'), sc.scalar(1.0, unit='cm'), sc.scalar(10.0, unit='mm')],
+)
+def test_gaussian_position_noise_is_sigma_unit_independent(sigma: sc.Variable) -> None:
+    sigma_m = sigma.to(unit='m')
+    reference = raw.gaussian_position_noise(sigma=sigma_m)
+    noise = raw.gaussian_position_noise(sigma=sigma)
+    assert sc.identical(noise, reference)
+
+
 def test_clear_counts_resets_counts_to_zero() -> None:
     detector_number = sc.array(dims=['pixel'], values=[1, 2, 3], unit=None)
     det = raw.Detector(detector_number)