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CHANGE RECORD
Table of contents
1. Introduction *
2. 2.1 Example HDSTRACE of WFCAM container file *3. WFCAM FITS headers *3.1 Definition of top level FITS headers *3.1.1 Example of top level FITS headers *3.2 Definition of frame level FITS headers *3.2.1 Example of frame level FITS headers *4. WFCAM WCS usage *4.1 CTYPEn FITS items *4.2 CRVAL and CRPIX FITS items *4.3 CD FITS items *4.4 PV FITS items *
This document illustrates the contents of a typical HDS container file into which WFCAM data is written and provides a list of FITS headers for that instrument. The FITS headers were based initially on those used for imaging with UIST but have been modified in the light of discussions, primarily in the area of the World Coordinate System headers.
Data from each of the four WFCAM cameras is to be written as NDF structures into separate HDS container files, usually as one file for each camera for each frame in a microstep pattern. For a microstep frame, each container holds two NDF structures:
The reason for having separate HEADER and I1 structures is to make it possible to add additional I2, I3 etc structures in the same container, with the contents of HEADER being common to all the frames. At present, this facility will be exploited for focus tests, with frames at multiple focus positions being written as separate NDF structures into the one container, each with its own focus setting encoded in its own frame level MORE.FITS. See the following section for a listing of the typical structure of a WFCAM HDS container file. Example HDSTRACE of WFCAM container file The following listing illustrates the structure of a typical WFCAM container file, generated using the HDSTRACE command. X20031020_00008 <UKIRT_HDS> I1 <NDF> {structure} DATA_ARRAY <ARRAY> {structure} DATA(2048,2048) <_INTEGER> 5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5, ... 21,21,21,21,21,21,21,21,21,21,21 ORIGIN(2) <_INTEGER> 1,1 HISTORY <HISTORY> {structure} CREATED <_CHAR*24> '2003-OCT-20 22:04:46.000' CURRENT_RECORD <_INTEGER> 1 RECORDS(10) <HIST_REC> {array of structures} Contents of RECORDS(1) DATE <_CHAR*24> '2003-OCT-20 22:04:46.000' COMMAND <_CHAR*9> '<unknown>' USER <_CHAR*5> 'wfcam' HOST <_CHAR*15> 'wfdr2.roe.ac.uk' DATASET <_CHAR*48> '/home/wfcam/data/raw/20031020/...' TEXT(2) <_CHAR*72> 'Arguments: <unknown>','Softwar...' AXIS(2) <AXIS> {array of structures} Contents of AXIS(1) DATA_ARRAY <ARRAY> {structure} DATA(2048) <_REAL> 0.5,1.5,2.5,3.5,4.5,5.5,6.5, ... 2044.5,2045.5,2046.5,2047.5 ORIGIN(1) <_INTEGER> 1 MORE <EXT> {structure} FITS(4) <_CHAR*80> 'UTSTART = 14.409722 /...' ... 'FOC_OFF = 0.00...' HEADER <NDF> {structure} DATA_ARRAY <ARRAY> {structure} DATA(1,1) <_REAL> 0 ORIGIN(2) <_INTEGER> 1,1 HISTORY <HISTORY> {structure} CREATED <_CHAR*24> '2003-OCT-20 22:04:47.000' CURRENT_RECORD <_INTEGER> 1 RECORDS(10) <HIST_REC> {array of structures} Contents of RECORDS(1) DATE <_CHAR*24> '2003-OCT-20 22:04:47.000' COMMAND <_CHAR*9> '<unknown>' USER <_CHAR*5> 'wfcam' HOST <_CHAR*15> 'wfdr2.roe.ac.uk' DATASET <_CHAR*52> '/home/wfcam/data/raw/20031020/...' TEXT(2) <_CHAR*72> 'Arguments: <unknown>','Softwar...' MORE <EXT> {structure} FITS(129) <_CHAR*80> ' ',' ...' ... 'DET_TEMP= 25....' End of Trace. WFCAM FITS headers Two tables are provided:
Each table lists the:
The possible sources of the FITS value are: • fix - the value is fixed in the header definition table; • om - set from the sequencer level of observation control via the OM Translator and the OOS task. This is likely to be blank (see below) when WFCAM is run from its non-OM engineering interface; • inst - set from the instrument control level (the WFIS); • TCS - read from the telescope control system; • EPICS - obtained from an EPICS database. When this is not available during engineering tests, this may be a fixed value; • data - obtained as attribute alongside data received from camera controller; • DHS - set within the DHS system; • CSO - obtained from CSO monitor task; • blank - the FITS value field will be blank Note that these sources are as seen from the point of view of the DHS. The ones in the "om" may, in turn, originate in some aspect of a survey definition, be specified by the Observer, or be specified or derived in some other way, for example from an entry in a lookup table read by the OT.
Definition of top level FITS headers
Example of top level FITS headers Identification: TELESCOP= 'UKIRT ' / Telescope name INSTRUME= 'WFCAM ' / Instrument CAMNUM = 2 / Number of WFCAM camera (1, 2, 3 or 4) DHSVER = 'UKDHS 2002 Oct 31 ' / Data handling version HDTFILE = 'wfcam.hdt ' / Name of global hdt file HDTFILE2= 'wfcam2.hdt ' / Name of camera-specific hdt file OBSERVER= 'Mrs Observer' / Observers names USERID = 'abc ' / Userid logged in as OBSREF = 'notPATT99' / PATT or other reference PROJECT = 'Example WFCAM data' / Time-allocation code SURVEY = 'Demo survey 123' / Survey name SURVEY_I= 'B1.99.4 ' / Pointing ID within survey MSBID = '42 ' / Id min.-schedulable block OBJECT = 'Laboratory wall' / Object name from telescope Data Reduction: RECIPE = 'QUICK_LOOK' / Data reduction recipe to be used OBSTYPE = 'OBJECT ' / BIAS|DARK|SKYFLAT|DOMEFLAT|OBJECT|SKY|FOCUS OBSNUM = 8 / Observation number GRPNUM = 8 / Group number applied to all members GRPMEM = T / Group membership TILENUM = 0 / Tile number applied to all members STANDARD= F / Is the target a standard star observation? NJITTER = 4 / Number of positions in tel jitter pattern JITTER_I= 1 / Serial number in this tel jitter pattern JITTER_X= 0.00 / [arcsec] X (RA) offset in tel jitter pattern JITTER_Y= 0.00 / [arcsec] Y (Dec) offset in tel jitter pattern NUSTEP = 4 / Number of positions in microstep pattern USTEP_I = 1 / Serial number in this microstep pattern USTEP_X = 0.00 / [arcsec] X (RA) offset in microstep pattern USTEP_Y = 0.00 / [arcsec] Y (Dec) offset in microstep pattern NFOC = 0 / Number of positions in focus scan NFOCSCAN= 0 / Number of focus scans in focus test Astrometric and time information: UTDATE = '20031020' / UT date as integer in yyyymmdd format DATE-OBS= '2003-10-20T14:24:35Z' / Date and time (UTC) of start of observation DATE-END= '2003-10-20T14:24:39Z' / Date and time (UTC) of end of observation MJD-OBS = 52932.60040 / DATE-OBS as Modified Julian Date WCSAXES = 2 / Number of axes in world co-ordinate system RADESYS = 'FK5 ' / Mean IAU 1984 equatorial co-ordinates EQUINOX = 2000.000 / [yr] Equinox of object position CTYPE1 = 'RA---ZPN' / Algorithm type for axis 1 CTYPE2 = 'DEC--ZPN' / Algorithm type for axis 2 CRPIX1 = -1000.0 / [pixel] Reference pixel along axis 1 (RA) CRPIX2 = -1000.0 / [pixel] Reference pixel along axis 2 (Rec) CRVAL1 = 300.16419 / [deg] Right ascension at the reference pixel CRVAL2 = 29.9749447 / [deg] Declination at the reference pixel CRUNIT1 = 'deg ' / Unit of right ascension co-ordinates CRUNIT2 = 'deg ' / Unit of declination co-ordinates CD1_1 = 0.000000E+00 / Transformation matrix element CD1_2 = -1.000000E+00 / Transformation matrix element CD2_1 = 5.000000E-01 / Transformation matrix element CD2_2 = -5.000000E-01 / Transformation matrix element PV2_1 = 1.000000E+00 / Pol.coeff. for pixel -> celestial coord PV2_2 = 0.000000E+00 / Pol.coeff. for pixel -> celestial coord PV2_3 = 7.500000E+01 / Pol.coeff. for pixel -> celestial coord RABASE = 20.0109458 / [h] Right ascension of base position DECBASE = 29.9749447 / [deg] Declination of base position TRAOFF = 0.000 / [arcsec] Right ascension telescope offset TDECOFF = 0.000 / [arcsec] Declination telescope offset AMSTART = 1.771 / Airmass at start of observation AMEND = 1.769 / Airmass at end of observation TELRA = 20.0123456 / [h] Current telescope right ascension TELDEC = 29.9876543 / [deg] Current telescope declination GSRA = 20.0103456 / [h] Right ascension of guide star GSDEC = 29.9806543 / [deg] Declination of guide star Instrument detector configuration: DETECTOR= 'RSC Hawaii 2' / Type of detector array used DETECTID= 'a.bc.234' / Serial number of detector array NINT = 1 / Number of integrations in observation DROWS = 2048 / [pixel] Number of detector rows DCOLUMNS= 2048 / [pixel] Number of detector columns RDOUT_X1= 1 / Start column of array readout RDOUT_X2= 2048 / Start column of array readout RDOUT_Y1= 1 / Start row of array readout RDOUT_Y2= 2048 / Start row of array readout PIXLSIZE= 0.4000 / [arcsec] Pixel size Detector controller: PCSYSID = 'wfacq2 ' / PC system identifier SDSUID = '00223 ' / Serial number of SDSU controller READMODE= 'CDS_v1 ' / Name of camera readmode CAPPLICN= 'applic01' / Name of camera readout application CAMROLE = 'master ' / Camera role (master|slave|unsync) READOUT = 'CDS ' / Camera readout (CDS|NDR|SAR|RRR) EXP_TIME= 1.000000 / [s] Integration time per exposure NEXP = 1 / Number of exposures in integration READINT = 1.000000 / [s] Interval between reads NREADS = 0 / Number of reads per exposure GAIN = 1.0 / [electrons/ADU] Detector gain Instrument optical configuration: FILTER = 'whatever' / Filter name FOC_MM = 12.34 / [mm] Base focus position Environment: AIRTEMP = 5.785 / [degC] Air temperature BARPRESS= 650.000 / Ambient pressure DEWPOINT= 2.000 / [degC] Dewpoint DOMETEMP= 7.095 / [degC] Dome temperature HUMIDITY= 35.450 / Relative humidity MIRRBSW = 7.123 / [degC] Temperature mirror B SW MIRRNE = 7.124 / [degC] Mirror temperature NE MIRRNW = 7.125 / [degC] Mirror temperature NW MIRRSE = 7.126 / [degC] Mirror temperature SE MIRRSW = 7.127 / [degC] Mirror temperature SW MIRRBTNW= 7.128 / [degC] Mirror bottom temp. NW MIRRTPNW= 7.129 / [degC] Mirror top temp. NW SECONDAR= 7.130 / [degC] Temperature of secondary TOPAIRNW= 7.131 / [degC] Top air NW TRUSSENE= 7.132 / [degC] Truss leg ENE TRUSSWSW= 7.133 / [degC] Truss leg WSW WIND_DIR= 106.987 / [deg] Wind direction, azimuth WIND_SPD= 16.089 / [km/h] Wind speed CSOTAU = 0.047 / Tau at 225 GHz from CSO TAUDATE = '2001-11-30T04:07' / Time and date of Tau reading TAUSRC = 'CSO ' / Source of opacity data Engineering: CNFINDEX= 1 / Configuration index DET_TEMP= 25.0 / [K] Detector array temperature
Example of frame level FITS headers
UTSTART = 14.409722 / [h] Start time of integration UTEND = 14.410833 / [h] End time of integration FOC_I = 0 / Serial number in focus scan FOC_OFF = 0.000 / [mm] Offset from base focus position
WFCAM WCS usage Several items in the top-level FITS headers are concerned with World Coordinate System (WCS) information. Thanks to Andy Vick for the explanations. Note that all but the CTYPEn values are candidates for being updated with new values during commissioning. CTYPEn FITS items CTYPE1 and CTYPE2 give the output format. That is to say, they give the format for the coordinates after you have applied all the transformations. In our case CTYPE1 is "RA---ZPN" and CTYPE2 is "DEC--ZPN". This implies that the transformation is a zenithal polynomial one.
These define the position of the reference pixel, which will initially be set to as near the optical axis of the instrument as possible.
The CD FITS items (CD1_1, etc) specify a transformation from pixel space with respect to reference point to projection plane coordinates with respect to reference point.
A comment in the FITS WCS document states in order to do a radial expansion, as in ZPN, then the coefficients go in the PV matrix keywords appropriate for the 'latitude' axis, which in our case is the second axis. The information is carried by the FITS keywords of the form PV2_n, and the PV1_n keywords are not used. The initial values are:
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