Update to use psfex as default PSF determiner

Test values changed slightly, but they are purely empirical; add a note
to the test to emphasize that for future developers.

python/lsst/pipe/tasks/measurePsf.py

@@ -25,6 +25,7 @@
 import lsst.meas.algorithms.utils as maUtils
 import lsst.pex.config as pexConfig
 import lsst.pipe.base as pipeBase
+import lsst.meas.extensions.psfex.psfexPsfDeterminer  # noqa: F401
 
 
 class MeasurePsfConfig(pexConfig.Config):
@@ -38,7 +39,7 @@ class MeasurePsfConfig(pexConfig.Config):
     )
     psfDeterminer = measAlg.psfDeterminerRegistry.makeField(
         "PSF Determination algorithm",
-        default="pca"
+        default="psfex"
     )
     reserve = pexConfig.ConfigurableField(
         target=measAlg.ReserveSourcesTask,

tests/test_processCcd.py

@@ -132,20 +132,27 @@ def testProcessCcd(self):
                     print("psf Ixx = %r, Iyy = %r, Ixy = %r" % (psfIxx, psfIyy, psfIxy))
 
                     self.assertEqual(len(icSrc), 28)
-                    self.assertEqual(len(src), 185 + 100)  # 185 real sources plus 100 sky sources
-
+                    self.assertEqual(len(src), 184 + 100)  # 184 real sources plus 100 sky sources
+
+                    # NOTE: These values are purely empirical, and need to be
+                    # updated to reflect major algorithmic changes.
+                    # If this test fails after an algorithmic change due to
+                    # small numeric changes here, check on slack at
+                    # #dm-science-pipelines as to whether the changes are
+                    # reasonable, and then replace the failing values by
+                    # running the test to determine the updated values.
                     expectedPlaces = 7  # Tolerance for numerical comparisons
                     for name, var, val in [
-                        ("bgMean", bgMean, 191.48635852060525),
-                        ("bgStdDev", bgStdDev, 0.2399466881603354),
-                        ("numGoodPix", numGoodPix, 1966820),
-                        ("imMean", imMean, 1.1237668985230562),
-                        ("imStdDev", imStdDev, 85.81296241298496),
+                        ("bgMean", bgMean, 191.48623786891795),
+                        ("bgStdDev", bgStdDev, 0.23994185672586282),
+                        ("numGoodPix", numGoodPix, 1966606),
+                        ("imMean", imMean, 1.1242456954648634),
+                        ("imStdDev", imStdDev, 85.8129750182329),
                         ("varMean", varMean, 131.24003624152013),
                         ("varStdDev", varStdDev, 55.98012493452948),
-                        ("psfIxx", psfIxx, 2.769679536557131),
-                        ("psfIyy", psfIyy, 2.2013649766299324),
-                        ("psfIxy", psfIxy, 0.14797939531970852)
+                        ("psfIxx", psfIxx, 2.843329671276296),
+                        ("psfIyy", psfIyy, 2.2249941554078156),
+                        ("psfIxy", psfIxy, 0.16073332780683286)
                     ]:
                         self.assertAlmostEqual(var, val, places=expectedPlaces, msg=name)
 

ups/pipe_tasks.table

@@ -8,6 +8,7 @@ setupRequired(utils)
 setupRequired(obs_base)
 setupRequired(meas_algorithms)
 setupRequired(meas_extensions_scarlet)
+setupRequired(meas_extensions_psfex)
 setupRequired(kht)
 setupOptional(meas_astrom)
 setupOptional(meas_deblender)