diff options
Diffstat (limited to 'stwcs/wcsutil')
| -rw-r--r-- | stwcs/wcsutil/hstwcs.py | 27 |
1 files changed, 21 insertions, 6 deletions
diff --git a/stwcs/wcsutil/hstwcs.py b/stwcs/wcsutil/hstwcs.py index 27f6467..aeaa43f 100644 --- a/stwcs/wcsutil/hstwcs.py +++ b/stwcs/wcsutil/hstwcs.py @@ -137,7 +137,8 @@ class HSTWCS(WCS): self.instrument = instrument_name # Set the correct reference frame refframe = determine_refframe(hdr0) - ehdr['RADESYS'] = refframe + if refframe is not None: + ehdr['RADESYS'] = refframe WCS.__init__(self, ehdr, fobj=phdu, minerr=self.minerr, key=self.wcskey) @@ -960,20 +961,34 @@ adaptive=False, detect_divergence=False, quiet=False) def determine_refframe(phdr): """ - Determine the reference frame in standard FITS WCS terms. + Determine the reference frame in standard FITS WCS. + + This is necessary for two reasons: + - The reference frame in HST images is stored not in RADESYS (FITS standard) but in REFFRAME. + - REFFRAME is in the primary header, while the rest of the WCS keywords are in the + extension header. + + The values of REFFRAME are populated from the APT template where observers are + given three options: GSC1 (corresponds to FK5), ICRS or OTHER. + In the case of "OTHER", we leave this to wcslib which has a default of ICRS. Parameters ---------- phdr : `astropy.io.fits.Header` Primary Header of an HST observation - In HST images the reference frame is recorded in the primary extension as REFFRAME. - Values are "GSC1" which means FK5 or ICRS (for GSC2 observations). + Returns + ------- + refframe : str or None + One of the FITS WCS standard reference frames. + """ try: - refframe = phdr['REFFRAME'] + refframe = phdr['REFFRAME'].upper() except KeyError: - refframe = " " + refframe = None if refframe == "GSC1": refframe = "FK5" + elif refframe != "ICRS": + refframe = None return refframe |