Add option to correct event times by a fixed shift

src/ctapipe_io_lst/__init__.py

@@ -19,7 +19,7 @@
     OpticsDescription,
     SizeType,
 )
-from astropy.time import Time
+from astropy.time import Time, TimeDelta
 
 from ctapipe.io import EventSource, read_table
 from ctapipe.io.datalevels import DataLevel
@@ -267,6 +267,12 @@ class LSTEventSource(EventSource):
         )
     ).tag(config=True)
 
+    event_time_correction_s = Float(
+        default_value=None,
+        allow_none=True,
+        help='If given, this number of seconds is *added* to the original event time. This is intendend to be used to correct wrong event timestamps due to wrong time on the White Rabbit switch.'
+    ).tag(config=True)
+
 
     classes = [PointingSource, EventTimeCalculator, LSTR0Corrections]
 
@@ -378,12 +384,14 @@ def __init__(self, input_url=None, **kwargs):
 
         self.read_pedestal_ids()
 
-
-
         if self.use_flatfield_heuristic is None:
             self.use_flatfield_heuristic = self.run_start < NO_FF_HEURISTIC_DATE
             self.log.info(f"Changed `use_flatfield_heuristic` to {self.use_flatfield_heuristic}")
 
+        self._event_time_correction = None
+        if self.event_time_correction_s is not None:
+            self._event_time_correction = TimeDelta(self.event_time_correction_s * u.s)
+
     @property
     def subarray(self):
         return self._subarray
@@ -634,6 +642,12 @@ def _generator(self):
 
             self.fill_mon_container(array_event, zfits_event)
 
+            # apply correction before the rest, so corrected time is used e.g. for pointing
+            if self._event_time_correction is not None:
+                array_event.trigger.time += self._event_time_correction
+                for tel_trigger in array_event.trigger.tel.values():
+                    tel_trigger.time += self._event_time_correction
+
             if self.pointing_information:
                 self.fill_pointing_info(array_event)
 

src/ctapipe_io_lst/tests/test_lsteventsource.py

@@ -356,3 +356,28 @@ def test_reference_position():
     assert u.isclose(position.lat, LST1_LOCATION.lat)
     assert u.isclose(position.lon, LST1_LOCATION.lon)
     assert u.isclose(position.height, LST1_LOCATION.height)
+
+
+
+
+@pytest.mark.parametrize("timeshift", (-5, 70))
+def test_time_correction(timeshift):
+    from ctapipe_io_lst import LSTEventSource
+    config = {
+        'LSTEventSource': {
+            'input_url': test_r0_path_all_streams,
+            'apply_drs4_corrections': False,
+            'pointing_information': False,
+            'max_events': 5,
+        },
+    }
+
+    original = LSTEventSource(config=Config(config))
+    shifted = LSTEventSource(config=Config(config), event_time_correction_s=timeshift)
+
+    with original, shifted:
+        for event, event_shifted in zip(original, shifted):
+            dt = event_shifted.trigger.time - event.trigger.time
+            dt_tel = event_shifted.trigger.tel[1].time - event.trigger.tel[1].time
+            assert u.isclose(dt.to_value(u.s), timeshift)
+            assert u.isclose(dt_tel.to_value(u.s), timeshift)