Apply 180 degree offset due to change in defintions

python/lsst/obs/lsst/translators/latiss.py

@@ -68,6 +68,10 @@
 # DATE-END is not to be trusted before this date
 DATE_END_IS_BAD = Time("2020-02-01T00:00", format="isot", scale="utc")
 
+# The convention for the reporting of ROTPA changed by 180 here
+ROTPA_CONVENTION_180_SWITCH1 = Time("2020-11-19T00:00", format="isot", scale="utc")
+ROTPA_CONVENTION_180_SWITCH2 = Time("2021-10-29T00:00", format="isot", scale="utc")
+
 # Scaling factor radians to degrees.  Keep it simple.
 RAD2DEG = 180.0 / math.pi
 
@@ -390,6 +394,10 @@ def fix_header(cls, header, instrument, obsid, filename=None):
                 if header[h]:
                     header[h] += offset
 
+        if date < ROTPA_CONVENTION_180_SWITCH2 and date > ROTPA_CONVENTION_180_SWITCH1:
+            header['ROTPA'] = header['ROTPA'] - 180
+            modified = True
+
         return modified
 
     def _is_on_mountain(self):