DM-16292: Propagate input headers to the output calibration files

python/lsst/pipe/drivers/constructCalibs.py

@@ -11,6 +11,9 @@
 from builtins import zip
 from builtins import range
 
+from astro_metadata_translator import merge_headers, ObservationGroup
+from astro_metadata_translator.serialize import dates_to_fits
+
 from lsst.pex.config import Config, ConfigurableField, Field, ListField, ConfigField
 from lsst.pipe.base import Task, Struct, TaskRunner, ArgumentParser
 import lsst.daf.base as dafBase
@@ -750,6 +753,8 @@ def combine(self, cache, struct, outputId):
             else:
                 calib = afwImage.DecoratedImageF(calib.getImage())  # n.b. hardwires "F" for the output type
 
+        self.calculateOutputHeaderFromRaws(cache.butler, calib, struct.ccdIdList, outputId)
+
         self.updateMetadata(calib, self.exposureTime)
 
         self.recordCalibInputs(cache.butler, calib,
@@ -761,6 +766,59 @@ def combine(self, cache, struct, outputId):
 
         return afwMath.binImage(calib.getImage(), self.config.binning)
 
+    def calculateOutputHeaderFromRaws(self, butler, calib, dataIdList, outputId):
+        """!Calculate the output header from the raw headers.
+
+        This metadata will go into the output FITS header. It will include all
+        headers that are identical in all inputs.
+
+        @param butler  Data butler
+        @param calib  Combined calib exposure.
+        @param dataIdList  List of data identifiers for calibration inputs
+        @param outputId  Data identifier for output
+        """
+        header = calib.getMetadata()
+
+        rawmd = [butler.get("raw_md", dataId) for dataId in dataIdList if
+                 dataId is not None]
+
+        merged = merge_headers(rawmd, mode="drop")
+
+        # Place merged set into the PropertyList if a value is not
+        # present already
+        # Comments are not present in the merged version so copy them across
+        for k, v in merged.items():
+            if k not in header:
+                comment = rawmd[0].getComment(k) if k in rawmd[0] else None
+                header.set(k, v, comment=comment)
+
+        # Create an observation group so we can add some standard headers
+        # independent of the form in the input files.
+        # Use try block in case we are dealing with unexpected data headers
+        try:
+            group = ObservationGroup(rawmd, pedantic=False)
+        except Exception:
+            group = None
+
+        comments = {"TIMESYS": "Time scale for all dates",
+                    "DATE-OBS": "Start date of earliest input observation",
+                    "MJD-OBS": "[d] Start MJD of earliest input observation",
+                    "DATE-END": "End date of oldest input observation",
+                    "MJD-END": "[d] End MJD of oldest input observation",
+                    "MJD-AVG": "[d] MJD midpoint of all input observations",
+                    "DATE-AVG": "Midpoint date of all input observations"}
+
+        if group is not None:
+            oldest, newest = group.extremes()
+            dateCards = dates_to_fits(oldest.datetime_begin, newest.datetime_end)
+        else:
+            # Fall back to setting a DATE-OBS from the calibDate
+            dateCards = {"DATE-OBS": "{}T00:00:00.00".format(outputId[self.config.dateCalib])}
+            comments["DATE-OBS"] = "Date of start of day of calibration midpoint"
+
+        for k, v in dateCards.items():
+            header.set(k, v, comment=comments.get(k, None))
+
     def recordCalibInputs(self, butler, calib, dataIdList, outputId):
         """!Record metadata including the inputs and creation details
 
@@ -778,8 +836,6 @@ def recordCalibInputs(self, butler, calib, dataIdList, outputId):
         now = time.localtime()
         header.add("CALIB_CREATION_DATE", time.strftime("%Y-%m-%d", now))
         header.add("CALIB_CREATION_TIME", time.strftime("%X %Z", now))
-        # add date-obs as its absence upsets ExposureInfo; use the mean date that the calibs were taken
-        header.add("DATE-OBS", "%sT00:00:00.00" % outputId[self.config.dateCalib])
 
         # Inputs
         visits = [str(dictToTuple(dataId, self.config.visitKeys)) for dataId in dataIdList if

ups/pipe_drivers.table

@@ -5,6 +5,7 @@ setupRequired(sphgeom)
 setupRequired(pex_config)
 setupRequired(pipe_base)
 setupRequired(pipe_tasks)
+setupRequired(astro_metadata_translator)
 
 envPrepend(PYTHONPATH, ${PRODUCT_DIR}/python)
 envPrepend(PATH, ${PRODUCT_DIR}/bin)