Merge pull request #478 from LSSTDESC/u/jchiang/opsim_db_dayobs_seqnum

bug-fix for seqnum calculation

imsim/opsim_data.py

@@ -116,7 +116,7 @@ def _read_opsim_db(self):
             # Determine the daily sequence number for this exposure by
             # counting the number of snaps since int(observationStartMJD)
             # with a half-day offset to account for Rubin's dayobs definition.
-            t0 = int(self.meta['observationStartMJD']) - 0.5
+            t0 = int(self.meta['observationStartMJD'] - 0.5) + 0.5
             sql = f'''select numExposures from observations where
                       {t0} <= observationStartMJD and
                       observationId < {self.visit}'''

tests/test_OpsimDataLoader.py

@@ -0,0 +1,27 @@
+from pathlib import Path
+import numpy as np
+from imsim import OpsimDataLoader
+
+DATA_DIR = Path(__file__).parent / "data"
+
+
+def test_seqnum_calculation():
+    """Test the values of seqnum computed by OpsimDataLoader from
+    an opsim db file."""
+    opsim_db_file = str(DATA_DIR / "opsim_db_seqnum_test_data.db")
+    visits = sorted(np.random.choice(range(2173), 10, replace=False))
+    for visit in visits:
+        opsim_data = OpsimDataLoader(opsim_db_file, visit=visit)
+        # The seqnum_ref column was added to an existing opsim db
+        # file.  It contains the sequence number computed by hand
+        # based on the definition of DAYOBS (See appendix A of
+        # https://docushare.lsst.org/docushare/dsweb/Get/LSE-400).
+        # The test data file contains an excerpt covering two days of
+        # observations.
+        assert opsim_data.meta["seqnum"] == opsim_data.meta["seqnum_ref"]
+
+
+if __name__ == "__main__":
+    testfns = [v for k, v in vars().items() if k[:5] == "test_" and callable(v)]
+    for testfn in testfns:
+        testfn()