Factor out ra/dec calculation

python/astro_metadata_translator/translators/decam.py

@@ -25,12 +25,13 @@
 
 import re
 
-from astropy.coordinates import EarthLocation, SkyCoord, AltAz, Angle
+from astropy.coordinates import EarthLocation, AltAz, Angle
 import astropy.units as u
 
 from ..translator import cache_translation
 from .fits import FitsTranslator
-from .helpers import altitude_from_zenith_distance, is_non_science
+from .helpers import altitude_from_zenith_distance, is_non_science, \
+    tracking_from_degree_headers
 
 
 class DecamTranslator(FitsTranslator):
@@ -169,21 +170,9 @@ def to_observation_type(self):
 
     @cache_translation
     def to_tracking_radec(self):
-        used = []
-        if "RADESYS" in self._header:
-            frame = self._header["RADESYS"].strip().lower()
-            used.append("RADESYS")
-            if frame == "gappt":
-                self._used_these_cards(*used)
-                # Moving target
-                return None
-        else:
-            frame = "icrs"
-        radec = SkyCoord(self._header["TELRA"], self._header["TELDEC"],
-                         frame=frame, unit=(u.hourangle, u.deg),
-                         obstime=self.to_datetime_begin(), location=self.to_location())
-        self._used_these_cards("TELRA", "TELDEC", *used)
-        return radec
+        radecsys = ("RADESYS",)
+        radecpairs = (("TELRA", "TELDEC"),)
+        return tracking_from_degree_headers(self, radecsys, radecpairs, unit=(u.hourangle, u.deg))
 
     @cache_translation
     def to_altaz_begin(self):

python/astro_metadata_translator/translators/helpers.py

@@ -34,9 +34,10 @@
 
 __all__ = ("to_location_via_telescope_name",
            "is_non_science",
+           "tracking_from_degree_headers",
            "altitude_from_zenith_distance")
 
-from astropy.coordinates import EarthLocation
+from astropy.coordinates import EarthLocation, SkyCoord
 import astropy.units as u
 
 
@@ -78,3 +79,54 @@ def altitude_from_zenith_distance(zd):
         Altitude.
     """
     return 90.*u.deg - zd
+
+
+def tracking_from_degree_headers(self, radecsys, radecpairs, unit=u.deg):
+    """Calculate the tracking coordinates from lists of headers.
+
+    Parameters
+    ----------
+    radecsys : `list` or `tuple`
+        Header keywords to try corresponding to the tracking system.  If none
+        match ICRS will be assumed.
+    pairs : `tuple` of `tuple` of pairs of `str`
+        Pairs of keywords containing the RA/Dec in units of ``unit``.
+    unit : `astropy.unit.BaseUnit` or `tuple`
+        Unit definition suitable for the `~astropy.coordinate.SkyCoord`
+        constructor.
+
+    Returns
+    -------
+    radec = `astropy.coordinates.SkyCoord`
+        The RA/Dec coordinates. None if this is a moving target or a
+        non-science observation without any RA/Dec definition.
+
+    Raises
+    ------
+    KeyError
+        No RA/Dec keywords were found and this observation is a science
+        observation.
+    """
+    used = []
+    for k in radecsys:
+        if k in self._header:
+            frame = self._header[k].strip().lower()
+            used.append(k)
+            if frame == "gappt":
+                self._used_these_cards(*used)
+                # Moving target
+                return None
+            break
+    else:
+        frame = "icrs"
+    for ra_key, dec_key in radecpairs:
+        print(f"RA: {ra_key}: {self._header[ra_key]} Dec: {dec_key}: {self._header[dec_key]}")
+        if ra_key in self._header and dec_key in self._header:
+            radec = SkyCoord(self._header[ra_key], self._header[dec_key],
+                             frame=frame, unit=unit, obstime=self.to_datetime_begin(),
+                             location=self.to_location())
+            self._used_these_cards(ra_key, dec_key, *used)
+            return radec
+    if self.to_observation_type() == "science":
+        raise KeyError("Unable to determine tracking RA/Dec of science observation")
+    return None

python/astro_metadata_translator/translators/megaprime.py

@@ -23,10 +23,11 @@
 
 __all__ = ("MegaPrimeTranslator", )
 
-from astropy.coordinates import EarthLocation, SkyCoord, AltAz, Angle
+from astropy.coordinates import EarthLocation, AltAz, Angle
 import astropy.units as u
 
 from .fits import FitsTranslator
+from .helpers import tracking_from_degree_headers
 
 filters = {'u.MP9301': 'u',
            'u.MP9302': 'u2',
@@ -131,28 +132,22 @@ def to_observation_type(self):
         return obstype
 
     def to_tracking_radec(self):
-        used = []
-        for k in ("RADECSYS", "OBJRADEC", "RADESYS"):
-            if k in self._header:
-                frame = self._header[k].strip().lower()
-                used.append(k)
-                if frame == "gappt":
-                    self._used_these_cards(*used)
-                    # Moving target
-                    return None
-                break
-        else:
-            frame = "icrs"
-        for ra_key, dec_key in (("RA_DEG", "DEC_DEG"), ("BORE-RA", "BORE-DEC")):
-            if ra_key in self._header and dec_key in self._header:
-                radec = SkyCoord(self._header[ra_key], self._header[dec_key],
-                                 frame=frame, unit=u.deg, obstime=self.to_datetime_begin(),
-                                 location=self.to_location())
-                self._used_these_cards(ra_key, dec_key, *used)
-                return radec
-        if self.to_observation_type() == "science":
-            raise KeyError("Unable to determine tracking RA/Dec of science observation")
-        return None
+        """Calculate the tracking RA/Dec for this observation.
+
+        Currently will be `None` for geocentric apparent coordinates.
+        Additionally, can be `None` for non-science observations.
+
+        The method supports multiple versions of header defining tracking
+        coordinates.
+
+        Returns
+        -------
+        coords : `astropy.coordinates.SkyCoord`
+            The tracking coordinates.
+        """
+        radecsys = ("RADECSYS", "OBJRADEC", "RADESYS")
+        radecpairs = (("RA_DEG", "DEC_DEG"), ("BORE-RA", "BORE-DEC"))
+        return tracking_from_degree_headers(self, radecsys, radecpairs)
 
     def to_altaz_begin(self):
         """Calculate the azimuth and elevation for the start of the