Add get_transmission_error_propogated()

mantidimaging/gui/windows/spectrum_viewer/model.py

@@ -178,6 +178,15 @@ def get_transmission_error_standard_dev(self, roi_name: str) -> np.ndarray:
         safe_divide = np.divide(sample, normed, out=np.zeros_like(sample), where=normed != 0)
         return np.std(safe_divide, axis=(1, 2))
 
+    def get_transmission_error_propogated(self, roi_name: str) -> np.ndarray:
+        if self._stack is None or self._normalise_stack is None:
+            raise RuntimeError("Sample and open beam must be selected")
+        roi = self.get_roi(roi_name)
+        sample = self.get_stack_spectrum_summed(self._stack, roi)
+        normed = self.get_stack_spectrum_summed(self._normalise_stack, roi)
+        error = np.sqrt(sample / normed**2 + sample**2 / normed**3)
+        return error
+
     def get_image_shape(self) -> tuple[int, int]:
         if self._stack is not None:
             return self._stack.data.shape[1:]
@@ -239,7 +248,7 @@ def save_rits(self, path: Path, normalized: bool, error_mode: ErrorMode) -> None
         if error_mode == ErrorMode.STANDARD_DEVIATION:
             transmission_error = self.get_transmission_error_standard_dev(ROI_RITS)
         elif error_mode == ErrorMode.PROPAGATED:
-            transmission_error = np.full_like(tof, 0.1)
+            transmission_error = self.get_transmission_error_propogated(ROI_RITS)
         else:
             raise ValueError("Invalid error_mode given")
 

mantidimaging/gui/windows/spectrum_viewer/test/model_test.py

@@ -221,6 +221,27 @@ def test_save_rits_roi_dat(self):
         self.assertIn("200000.0\t1.5\t0.5", mock_stream.captured[2])
         self.assertTrue(mock_stream.is_closed)
 
+    @parameterized.expand([
+        ("std_dev", ErrorMode.STANDARD_DEVIATION, [0., 0.25, 0.5, 0.75, 1., 1.25, 1.5, 1.75, 2., 2.25]),
+        ("std_dev", ErrorMode.PROPAGATED,
+         [0.0000, 0.0772, 0.1306, 0.1823, 0.2335, 0.2845, 0.3354, 0.3862, 0.4369, 0.4876]),
+    ])
+    def test_save_rits_data_errors(self, _, error_mode, expected_error):
+        stack, _ = self._set_sample_stack(with_tof=True)
+        norm = ImageStack(np.full([10, 11, 12], 2))
+        stack.data[:, :, :5] *= 2
+        self.model.set_new_roi("rits_roi")
+        self.model.set_roi("rits_roi", SensibleROI.from_list([0, 0, 10, 11]))
+        self.model.set_normalise_stack(norm)
+
+        mock_stream, mock_path = self._make_mock_path_stream()
+        with mock.patch.object(self.model, "save_roi_coords"):
+            with mock.patch.object(self.model, "export_spectrum_to_rits") as mock_export:
+                self.model.save_rits(mock_path, True, error_mode)
+
+        calculated_errors = mock_export.call_args[0][3]
+        np.testing.assert_allclose(expected_error, calculated_errors, atol=1e-4)
+
     @parameterized.expand([("standard_deviation", ErrorMode.STANDARD_DEVIATION), ("propagated", ErrorMode.PROPAGATED)])
     def test_error_mode_rits(self, _, error_mode):
         stack, _ = self._set_sample_stack(with_tof=True)