Merge pull request #64 from scipp/to-event-data

Add method to generate data that resembles nxevent_data

src/tof/result.py

@@ -379,3 +379,30 @@ def __repr__(self) -> str:
 
     def __str__(self) -> str:
         return self.__repr__()
+
+    def to_nxevent_data(self, key: str) -> sc.DataArray:
+        """
+        Convert a component reading to event data that resembles event data found in a
+        NeXus file.
+
+        Parameters
+        ----------
+        key:
+            Name of the component.
+        """
+        start = sc.datetime("2024-01-01T12:00:00.000000")
+        period = sc.reciprocal(self.source.frequency)
+        raw_data = self[key].data.flatten(to='event')
+        # Select only the neutrons that make it to the detector
+        event_data = raw_data[~raw_data.masks['blocked_by_others']].copy()
+        dt = period.to(unit=event_data.coords['toa'].unit)
+        event_time_zero = (dt * (event_data.coords['toa'] // dt)).to(dtype=int) + start
+        event_data.coords['event_time_zero'] = event_time_zero
+        event_data.coords['event_time_offset'] = event_data.coords.pop(
+            'toa'
+        ) % period.to(unit=dt.unit)
+        return (
+            event_data.drop_coords(['tof', 'speed', 'time', 'wavelength'])
+            .group('event_time_zero')
+            .rename_dims(event_time_zero='pulse')
+        )

tests/model_test.py

@@ -387,3 +387,44 @@ def test_component_distance():
     assert sc.identical(res['monitor'].data.coords['distance'], monitor.distance)
     assert sc.identical(res['detector'].data.coords['distance'], detector.distance)
     assert sc.identical(res['chopper'].data.coords['distance'], chopper.distance)
+
+
+def test_to_nxevent_data():
+    source = tof.Source(facility='ess', neutrons=100_000)
+    choppers = [
+        tof.Chopper(
+            frequency=14.0 * Hz,
+            open=sc.array(
+                dims=['cutout'],
+                values=[0.0],
+                unit='deg',
+            ),
+            close=sc.array(
+                dims=['cutout'],
+                values=[10.0],
+                unit='deg',
+            ),
+            phase=90.0 * deg,
+            distance=8.0 * meter,
+            name="chopper",
+        )
+    ]
+    detectors = [
+        tof.Detector(distance=26.0 * meter, name='monitor'),
+        tof.Detector(distance=32.0 * meter, name='detector'),
+    ]
+    model = tof.Model(source=source, choppers=choppers, detectors=detectors)
+    res = model.run()
+
+    # There should be 1 pulse for monitor data, and 2 pulses for detector data as it
+    # wraps around the pulse period.
+    for key, npulses in zip(('monitor', 'detector'), (1, 2)):
+        nxevent_data = res.to_nxevent_data(key)
+        assert sc.identical(res['monitor'].data.sum().data, nxevent_data.sum().data)
+        assert nxevent_data.sizes['pulse'] == npulses
+        assert nxevent_data.bins.concat().value.coords[
+            'event_time_offset'
+        ].min() >= sc.scalar(0.0, unit='us')
+        assert nxevent_data.bins.concat().value.coords[
+            'event_time_offset'
+        ].max() <= sc.reciprocal(source.frequency).to(unit='us')