FITS metadata for lsst.afw.image Exposures

ExposureInfo and contents such as Filter and VisitInfo can be stored as FITS header keywords. The catalog schemas are described in ExposureInfo.cc, Filter.cc, and VisitInfo.cc. This page describes the equivalent FITS header keywords.

HDU 0

Keyword Format Units Accessor [1] and description
DETNAME str  

Detector.getAmpInfo

Detector name.

DETSER str  

Detector.getAmpInfo

Detector serial number.

EXPID long int  

VisitInfo.getExposureId

Exposure ID.

EXPTIME float sec

VisitInfo.getExposureTime

Exposure duration (shutter open time).

DARKTIME float sec

VisitInfo.getDarkTime

Time from CCD flush to readout, including shutter open time (despite the name)

DATE-AVG ISO8601  

VisitInfo.getDate

Date at middle of exposure, at boresight. No time zone character allowed.

TIMESYS str   Must exist and must be set to "TAI" if DATE-AVG is present.
TIME-MID ISO8601  

VisitInfo.getDate

Deprecated; read if DATE-AVG not found, for backwards compatibility. Date at middle of exposure. The time zone character must exist and must be "Z". Note: TIME-MID is always UTC (even if the comment claims it is TAI) and TIMESYS is ignored.

MJD-AVG-UT1 float MJD

VisitInfo.getUt1

UT1 date middle of exposure, at boresight

AVG-ERA float deg

VisitInfo.getEra

Earth rotation angle at middle of exposure, at boresight.

BORE-RA float deg

VisitInfo.getBoreRaDec

Position of boresight, ICRS RA.

BORE-DEC float deg

VisitInfo.getBoreRaDec

Position of boresight, ICRS Dec.

BORE-AZ float deg

VisitInfo.getBoreAzAlt

Position of boresight, refracted apparent topocentric Az.

BORE-ALT float deg

VisitInfo.getBoreAzAlt

Position of boresight, refracted apparent topocentric Alt.

BORE-ROTANG float deg

VisitInfo.getBoreRotAngle

Orientation of rotator at boresight.

ROTTYPE str  

VisitInfo.getRotType

Type of rotation; one of:

  • UNKNOWN
  • SKY: position angle of focal plane +Y measured from N through E.
  • HORIZON: position angle of focal plane +Y measured from +Alt through +Az.
  • MOUNT: the position sent to the instrument rotator; the details depend on the rotator.
OBS-LONG float deg VisitInfo.getObservatory Longitude of telescope.
OBS-LAT float deg

VisitInfo.getObservatory

Latitude of telescope (positive eastward).

OBS-ELEV float m

VisitInfo.getObservatory

Geodetic elevation of telescope (meters above reference spheroid).

AIRTEMP float C

VisitInfo.getWeather

Air temperature.

AIRPRESS float Pascals

VisitInfo.getWeather

Air pressure.

HUMIDITY float %

VisitInfo.getWeather

Relative humidity.

FILTER str  

Filter.getName

Name of filter.

AR_HDU int   HDU containing the archive used to store ancillary objects
COADD_INPUTS_ID int   Archive ID for coadd inputs catalogs
AP_CORR_MAP_ID int   Archive ID for aperture correction map
PSF_ID int   Archive ID for the Exposure’s main Psf
WCS_ID int   Archive ID for the Exposure’s main Wcs
VALID_POLYGON_ID int   Archive ID for the Exposure’s valid polygon
ARCHIVE_ID_[name] int  

getComponent("[name]")

Archive ID for an arbitrary Exposure component

HDUs 1 to 3

Keyword Format Units Accessor [1] and description
CRPIX1A double pixels X axis reference pixel, always 1.0.
CRPIX2A double pixels Y axis reference pixel, always 1.0.
CRVAL1A double  

Exposure.getXY0

Access as exposure.getXY0[0].

CRVAL2A double  

Exposure.getXY0

Access as exposure.getXY0[1].

CTYPE1A str   Always "LINEAR".
CTYPE2A str   Always "LINEAR".
CUNIT1A str   Always "PIXEL".
CUNIT2A str   Always "PIXEL".
[1](1, 2) Unless otherwise noted, each object is contained in the ExposureInfo and has a getter. Thus to get VisitInfo use exposure.getExposureInfo().getVisitInfo(). In some cases a direct shortcut is also available, e.g. exposure.getFilter() is a shortcut for exposure.getExposureInfo().getFilter().