Change the makeDiscreteSkyMap interface to use bbox

Both gen2 and gen3 butler can return the bounding box directly
so there is no need to derive it from metadata. In gen3 the
metadata does not include the NAXIS parameters so it is
impossible to calculate the bbox from it.

python/lsst/pipe/tasks/makeDiscreteSkyMap.py

@@ -24,7 +24,6 @@
 import lsst.sphgeom
 
 import lsst.geom as geom
-import lsst.afw.image as afwImage
 import lsst.pex.config as pexConfig
 import lsst.pipe.base as pipeBase
 from lsst.skymap import DiscreteSkyMap, BaseSkyMap
@@ -142,47 +141,45 @@ def runDataRef(self, butler, dataRefList):
         struct : `lsst.pipe.base.Struct`
            The returned struct has one attribute, ``skyMap``, which holds the returned SkyMap
         """
-        wcs_md_tuple_list = []
+        wcs_bbox_tuple_list = []
         oldSkyMap = None
         datasetName = self.config.coaddName + "Coadd_skyMap"
         for dataRef in dataRefList:
             if not dataRef.datasetExists("calexp"):
                 self.log.warning("CalExp for %s does not exist: ignoring", dataRef.dataId)
                 continue
-            wcs_md_tuple_list.append((dataRef.get("calexp_wcs", immediate=True),
-                                      dataRef.get("calexp_md", immediate=True)))
+            wcs_bbox_tuple_list.append((dataRef.get("calexp_wcs", immediate=True),
+                                        dataRef.get("calexp_bbox", immediate=True)))
         if self.config.doAppend and butler.datasetExists(datasetName):
             oldSkyMap = butler.get(datasetName, immediate=True)
             if not isinstance(oldSkyMap.config, DiscreteSkyMap.ConfigClass):
                 raise TypeError("Cannot append to existing non-discrete skymap")
             compareLog = []
             if not self.config.skyMap.compare(oldSkyMap.config, output=compareLog.append):
                 raise ValueError("Cannot append to existing skymap - configurations differ:", *compareLog)
-        result = self.run(wcs_md_tuple_list, oldSkyMap)
+        result = self.run(wcs_bbox_tuple_list, oldSkyMap)
         if self.config.doWrite:
             butler.put(result.skyMap, datasetName)
         return result
 
     @pipeBase.timeMethod
-    def run(self, wcs_md_tuple_list, oldSkyMap=None):
+    def run(self, wcs_bbox_tuple_list, oldSkyMap=None):
         """Make a SkyMap from the bounds of the given set of calexp metadata.
 
         Parameters
         ----------
-        wcs_md_tuple_list : iterable
-           A list of tuples with each element expected to be a (Wcs, PropertySet) pair
+        wcs_bbox_tuple_list : iterable
+           A list of tuples with each element expected to be a (Wcs, Box2I) pair
         oldSkyMap : `lsst.skymap.DiscreteSkyMap`, option
            The SkyMap to extend if appending
         Returns
         -------
         struct : `lsst.pipe.base.Struct
            The returned struct has one attribute, ``skyMap``, which holds the returned SkyMap
         """
-        self.log.info("Extracting bounding boxes of %d images", len(wcs_md_tuple_list))
+        self.log.info("Extracting bounding boxes of %d images", len(wcs_bbox_tuple_list))
         points = []
-        for wcs, md in wcs_md_tuple_list:
-            # nb: don't need to worry about xy0 because Exposure saves Wcs with CRPIX shifted by (-x0, -y0).
-            boxI = afwImage.bboxFromMetadata(md)
+        for wcs, boxI in wcs_bbox_tuple_list:
             boxD = geom.Box2D(boxI)
             points.extend(wcs.pixelToSky(corner).getVector() for corner in boxD.getCorners())
         if len(points) == 0:

python/lsst/pipe/tasks/script/makeDiscreteSkyMap.py

@@ -76,7 +76,7 @@ def makeDiscreteSkyMap(repo, config_file, collections, instrument,
 
     datasets = butler.registry.queryDatasets('calexp', collections=collections)
     wcs_md_tuple_list = [(butler.getDirect(ref.makeComponentRef("wcs")),
-                          butler.getDirect(ref.makeComponentRef("metadata")))
+                          butler.getDirect(ref.makeComponentRef("bbox")))
                          for ref in datasets]
     task = MakeDiscreteSkyMapTask(config=config)
     result = task.run(wcs_md_tuple_list, oldSkyMap)