Full tract background refactor AEW

All methods, including run, updated to function properly with
tract backgrounds rather than warps.  Task completes without
error when run on three full visits, and output appears roughly
correct.

Author: aemerywatkins

python/lsst/pipe/tasks/background.py

@@ -860,7 +860,7 @@ class TractBackgroundConfig(Config):
     )
     doSmooth = Field(dtype=bool, default=False, doc="Do smoothing?")
     smoothScale = Field(dtype=float, default=2.0, doc="Smoothing scale, as a multiple of the bin size")
-    binning = Field(dtype=int, default=64, doc="Binning to use for warp background model (pixels)")
+    binning = Field(dtype=int, default=200, doc="Binning to use for warp background model (pixels)")
 
 
 class TractBackground:
@@ -895,8 +895,6 @@ def __init__(self, config, values=None, numbers=None):
         ----------
         config : `TractBackgroundConfig`
             Configuration for measuring tract backgrounds.
-        transform : `lsst.afw.geom.TransformPoint2ToPoint2`
-            Transformation from tract coordinates to warp coordinates.
         values : `lsst.afw.image.ImageF`
             Measured background values.
         numbers : `lsst.afw.image.ImageF`
@@ -1097,7 +1095,10 @@ def getStatsImage(self):
         """
         values = self._values.clone()
         values /= self._numbers
-        # This old logic doesn't work because everything outside the FP is bad
+        # TODO: this logic smoothes over bad parts of the image, including NaN
+        # values.  But it doesn't work here because NaN pixels are always found
+        # at the image edges.  Could ignore it, or devise an alternative.
+        # tract have no overlap with the visit?
         # thresh = self.config.minFrac * (self.config.xBin) * (self.config.yBin)
         # isBad = self._numbers.getArray() < thresh
         # if self.config.doSmooth: