DD Variables useful for Instrument UIs and Image Headers

Below is a list of TCS Data Dictionary (DD) variables that instruments may find useful, along with suggested FITS header keyword matchings for them where appropriate. Some of the values will be of interest for display on the instrument User's Interface (UI), while others are purely intended for telescope engineering purposes at this time. Note that all of the sided examples below are listed as "S_". This means there is a "L_" for left side and "R_" for the right side.Archive-specific header keywords are listed on this link for Archive Keywords.

Parameters sent from instrument to position the telescope:

This section includes observation configuration information supplied by the user. Some of it gets copied into the DD for use by the TCS, but everything in this section should be available to the instrument without reading it back from the DD.

DD variable name FITS Keyword Description
  OBJNAME Name of the Target
  OBJECT Identifier observation title
  OBJDEC Requested Dec. in degrees (given by OB). Should use info instrument sent
  OBJRA Requested R.A. in hours (given by OB). Should use info instrument sent
  OBJPMRA Proper motion for R.A. in mas/yr
  OBJPMDEC Proper motion for DEC. in mas/yr
  OBJEPOCH Coordinates epoch of OBJRA and OBJDEC
  OBJPA Requested position angle
  ROTMODE Requested rotator mode (position or parallactic)
  TELMODE Requested telescope mode (track, guide, active, adaptive)

  • Similar data exists for the guide star and for the AO reference star as supplied to the TCS. These data should be written into the headers under a parallel naming scheme (e.g. GSNAME, GSRA, GSDEC, etc.) but the data does not need to be read back from the TCS.

  • For any quantities that change during an exposure (UTC, LST, Airmass, etc.) the instrument is free to define if the values in the headers correspond to the beginning or end of an exposure as long as it is clear in the header.

General Information:

This section contains information that is of astronomical interest (e.g. UT, LST, Airmass). Some of the quantities are constantly changing during science exposures. We leave it up to the instrument teams to define if the values in the headers correspond to the beginning or end of an exposure as long as it is clear in the FITS keyword description field. Note that the RA and DEC read back from the DD below shows the current position of the telescope, even during slews, for the current date and time, after application of any proper motion and precession. These values are for an EPOCH corresponding to right then (e.g. 2010.123456) but are always EQUINOX=J2000.

DD variable name FITS Keyword Description
S_Instrument   Check the authorized instrument
UTC UTC_OBS Current UTC (instrument can define if this is the start or end of exposures
  ZD Zenith distance (degrees). Calculated from (90 - TELALT)?
AirMass AIRMASS Airmass. Calculated from 1/cos(ZD)?.
  HA Hour Angle (+East, -West). Calculated from OBSRA - LST_OBS?
S_AchievedRAHMS RA The current RA of the telescope. Changes during slews, Epoch=NOW!
S_AchievedDECDMS DEC The current DEC of the telescope. Changes during slews, Equinox=J2000
  EPOCH The current EPOCH of the observation
AZPosition TELAZ The current AZ of the telescope
ELPosition TELALT The current ALt (EL) of the telescope
S_FBGRPosition ROTANGLE The physical rotator angle (asec). Covers the full [-90,450] degree range
ParAngle PARANGLE The current parallactic angle
S_PosAngle POSANGLE The current position angle
  MEANFWHM Mean site FWHM, corrected to std Vband @ 1airmass
  TIME2LIM Time to hit a limit (whatever is first)
  TIME2SET Time to set (go below some operational EL limit)

GCS status
DD variable name FITS Keyword Description
S_GuideFlag ISGUIDED Boolean isGuiding flag, states if GCS is running the guide loop. Guiding could still be paused or not effective due to lost guide star
S_GuideHotspotX GSKFP_X Guide star kernel focal plane X coordinate
S_GuideHotspotY GSKFP_Y Guide star kernel focal plane Y coordinate
  IGSFWHM Instantaneous (last) guide star FWHM
  MGSFWHM Mean (since isCollimated) guide star FWHM
  MGSXRMS Mean (since isCollimated) guide star X rms
  MGSYRMS Mean (since isCollimated) guide star Y rms

WFS status
DD variable name FITS Keyword Description
S_WFSIsCollimated ISCOLLIM Boolean isCollimated flag
S_WFSRMS IWFSRMS Instantaneous (last) WFS rms (initialized to 0.0)
    Human-readable (string) time of last transfer of Z's to PSF
  MWFSRMS Mean (since isCollimated) WFS rms

  • The boolean isCollimated flag is set to zero on all presets and any offsets exceeding a couple of arcsec. It is set back to one when a successful wfs cycle shows an rms wavefront error below some configurable threshold (currently 600nm). This is the flag to watch if you want to "wait for collimation" prior to starting science observations. The time of last update can be watched to monitor if the wfs is stale or not.

Adaptive-Optics Quantities (AO Team to define these?)
S_AOLoopOn AOCLOSED Boolean: Is the AO loop closed

WCS data:
DD variable name FITS Keyword Description

  • The same quantities for RA and DEC are also available as radians in S_RotCenterRA and S_RotCenterDEC.
  • The pointing kernel can provide a complete WCS for the image. It gives the position of the pointing origin in the telescope focal plane and the coordinates (e.g. on-sky for the RADEC coordinate system) corresponding to that position. This is not yet implemented in the TCS, but it is the correct way to define a WCS for the data. LUCIFER currently implements the WCS by retrieving the coordinates of the rotator center from the DD and writing a fixed CRPIX1/2 value corresponding to the last measurement of the rotator center position on the detector.

Telescope Collimation data:
DD variable name FITS Keyword Description
S_M1CollX M1_POSX Primary mirror position in X
S_M1CollY M1_POSY Primary mirror position in Y
S_M1CollZ M1_POSZ Primary mirror position in Z
S_M1CollRx M1_ROTX Primary mirror rotation around X
S_M1CollRy M1_ROTY Primary mirror rotation around Y
S_M1CollRz M1_ROTZ Primary mirror rotation around Z
S_M1CollTemp M1CTEMP Primary mirror glass temperature (Collimation Temp)
S_M1AirTemp M1ATEMP Primary mirror air temperature
S_M2CollX M2_POSX Secondary mirror position in X
S_M2CollY M2_POSY Secondary mirror position in Y
S_M2CollZ M2_POSZ Secondary mirror position in Z
S_M2CollRx M2_ROTX Secondary mirror rotation around X
S_M2CollRy M2_ROTY Secondary mirror rotation around Y
S_M2CollRz M2_ROTZ Secondary mirror rotation around Z
S_M2CollTemp M2CTEMP Secondary mirror glass temperature. Is there no glass temp sensor at M2?
  M2ATEMP Secondary mirror air temperature. Is there no air temp sensor at M2?
S_M3CollTip M3__TIP Tertiary mirror tip
S_M3CollTilt M3_TILT Tertiary mirror tilt
S_M3CollPiston M3_PSTN Tertiary mirror piston
S_M3CollSel M3_ZROT Tertiary mirror rotation around Z axis
S_M3CollTemp M3CTEMP Tertiary mirror glass temperature. Is there no glass temp sensor at M3?
  M3ATEMP Tertiary mirror air temperature. Is there no air temp sensor at M3?

Telescope Temperature Sensors
DD variable name FITS Keyword Description
Temp201 TTEMP201 Middle C ring steel
Temp202 TTEMP202 Middle C ring air
Temp203 TTEMP203 Upper C ring steel
Temp204 TTEMP204 Upper C ring air
Temp205 TTEMP205 Lower C ring steel
Temp206 TTEMP206 Lower C ring air
Temp207 TTEMP207 Right lower wind brace steel
Temp208 TTEMP208 Right lower wind brace air
Temp209 TTEMP209 Right mirror cell brace steel
Temp210 TTEMP210 Right mirror cell brace air
Temp301 TTEMP301 Right C ring extension steel
Temp302 TTEMP302 Right C ring extension air
Temp303 TTEMP303 Left C ring extension steel
Temp304 TTEMP304 Left C ring extension air
Temp305 TTEMP305 Upper wind brace steel
Temp306 TTEMP306 Upper wind brace air
Temp307 TTEMP307 Right middle wind brace steel
Temp308 TTEMP308 Right middle wind brace air
Temp309 TTEMP309 Left middle wind brace steel
Temp310 TTEMP310 Left middle wind brace air

Weather information
DD variable name FITS Keyword Description
SMTPressure SMTPRESA SMT Ambient air pressure (units)
SMTTemp SMTTEMPA SMT Ambient temperature (C)
SMTHumidity SMTHUMID SMT Relative humidity (%)
SMTDewPoint SMTDEWPT SMT Dew point (C)
LBTPressure LBTPRESA LBT Ambient air pressure (units)
LBTTemp LBTTEMPA LBT Ambient temperature (C)
LBTHumidity LBTHUMID LBT Relative humidity (%)
LBTDewPoint LBTDEWPT LBT Dew point (C)
LBTWIndSpeed WINDSPD LBT Wind speed
LBTWindDir WINDDIR LBT Wind direction (AZ)


The information in this section has yet to be formatted for the wiki. It covers the current (March 2010) state of the LBC cameras and the telescope information written into the headers.

DD variable name FITS Keyword Description
OBJNAME name of the Target OBJECT Identifier observation title OBJRA commanded R.A. in hours (given by OB) OBJDEC commanded Dec. in degree (given by OB) PMRA Proper motion for R.A. in arcsec/hour Change to OBJPMRA PMDEC Proper motion for DEC. in arcsec/hour Change to OBJPMDE OBJEPOCH coordinates epoch of OBJRA and OBJDEC POSANGLE Requested position angle Need to add this

### Include ROTMODE (position or parallactic) and TELMODE (track, guide, active)

### For POSANGLE, PARANGLE, and ROTANGLE, I would prefer these keywords be used for the value in effect at the time the data were taken, ### and use OBJPA to specify the requested position (or parallactic) angle.

### The OBJRA and OBJDEC can be read back from the telescope as noted above, but this information is supplied by the ### instrument and therefore should not need to be read back (unless it is for a sanity check).

### NB: OBJRA, OBJDEC are only written into headers when coming from a preset in an OB! For example, they are ### missing for observations taken with the DEC=-90 flag (take image here).

### DD variable name FITS Kwd Description Notes/Change/Add: #=========================================================================================================================================================================== ParAngle PARANGLE Parallactic Angle [deg] Current parallactic angle

PA_PNT Position Angle of the pointing [deg] call this "Acheived PA" ROTANGLE Rotator Angle [deg] LST LST_OBS ST at start UTC UTC_OBS UT at start S_AchievedRA TELRA actual R.A. in radians (from TCS) = OBSRA ? S_AchievedDEC TELDEC actual DEC. in radians (from TCS) = OBSDEC ? OBSEPOCH coordinates epoch of OBSRA and OBSDEC Should be e.g.: 2010.123 (today's decimal date)

### The quantities read back for TELRA and TELDEC are proper-motion and precession corrected Equinox J2000 coordinates, so ### OBSEPOCH should actually reflect the epoch of the observation, not the epoch of the specified source coordinates!

S_AchievedAZ TELAZ Az angle at start N=0,E=+90 (from TCS) Change to mcs.azDrive.position S_AchievedALT TELALT Alt angle at start (from TCS) Change to mcs.elDrive.position

LBTPRessure LBTPRES Ambient air pressure [mbar] (from TCS) LBTHumidity LBTRHUM Ambient relative humidity [%] (from TCS) LBTTemp LBTTEMP Ambient temperature [Celsius] (from TCS) LBTWindDir LBTWNDIR Ambient wind direction [deg] (from TCS) LBTWindSpeed LBTWNSPD Ambient wind speed [m/s] (from TCS) LBTDewPoint LBTDEWPT Not found in LBC header[0]

### You can also read SMT* and write parallel information to keywords starting with SMT* as above. ### The env.weather.* entries are active now, please change LBC to using these as soon as possible.

S_M1CollX MIRRORX Primary mirror X position [mm] S_M1CollY MIRRORY Primary mirror Y position [mm] S_M1CollZ MIRRORZ Primary mirror Z position [mm] S_M1CollRx MIRRORRX Primary mirror RX rotation [arcsec] S_M1CollRy MIRRORRY Primary mirror RY rotation [arcsec] S_M1CollRz MIRRORRZ Primary mirror RZ rotation [arcsec] S_M1CollTemp M1CTEMP Primary Mirror glass temperature S_M1AirTemp M1ATEMP Primary mirror air temperature

### LBC Collimation models have apparently been made to date using the SMT temperatures! It would be much better to use ### the temperature that the primary mirror uses to do the temperature corrections to the collimation models. Add at least ### M1CTEMP (M1 collimation temperature) to the LBC headers, adding M1ATEMP is optional.

* Generalize anything that contains 'LBC' in the keyword if possible:*
LBCOBNAM Observing Block ID Change to OBNAME (supplied by observer)
LBCOBFIL [no fits comment] Change to OBARCH (as written to archive)
LBCOBID Observing Block ID ?
LBCUSER P.I. Name Change to PI_NAME
OBSERVER Observer Name Change to PARTNER
Use OBSERVER for the person at the telescope taking data
LBCPIPEC Command to be executed on the image
LBCNCHIP Number of active chips in LBC camera
LBCCHIP1 1st chip status (1=on 0=off)
LBCCHIP2 2nd chip status (1=on 0=off)
LBCCHIP3 3rd chip status (1=on 0=off)
LBCCHIP4 4th chip status (1=on 0=off)
LBCBIN Binning of the Pixels
LBCSPRED Pixel reading speed (0=normal, 1=fast)
LBCBACK Background from technical chips [ADU]


The information in this section has yet to be formatted for the wiki. It covers the current (March 2010) state of LUCIFER and the telescope information written into the headers. Only listed here are things currently retrieved from the DD that LBTO would prefer be changed to match the list above.

S_AGWHappy Torsten said do not rely on these
S_AGWState Torsten said do not rely on these
S_GuideRA Supplied by observer - no need to read these back
S_GuideDEC Supplied by observer - no need to read these back
S_GuideBadCount See first section for update/suggestions

S_RotAngle The computed rotator angle from the pcs subsystem
S_Instrument The authorized instrument


These are particular additional DD entries used by MODS image FITS headers and their corresponding header keywords.

Rotation Angles

All units are in degrees in the FITS header

DD variable name FITS Keyword Description
S_ParAngle PARANGLE Parallactic Angle
S_PosAngle POSANGLE Celestial/Parallactic Position Angle
S_RotAngle ROTANGLE Rotator Angle
S_RotMode ROTMODE Rotator Mode (Position or Parallactic)

GCS- and PCS-based AGw and Guide-Star Parameters

All units are in millimeters

DD variable name FITS Keyword Description
S_AGWKFPReqX GPREQ_X Requested Guide Probe X
S_AGWKFPReqY GPREQ_Y Requested Guide Probe Y
S_AGWKFPPosX GPACT_X Achieved Guide Probe X
S_AGWKFPposY GPACT_Y Achieved Guide Probe Y
S_GSXPredicted GSPRED_X Predicted guide star X
S_GSYPredicted GSPRED_Y Predicted guide star Y
S_GSXMeasured GSMEAS_X Measured guide star X
S_GSYMeasured GSMEAS_Y Measured guide star Y
S_GSCumXPredmMeas GSDELTAX difference in X
S_GSCumYPredmMeas GSDELTAY difference in Y

MCS-based Telescope Alt/El and raw Rotator parameters

All are in units of decimal degrees in the FITS headers

DD variable name FITS Keyword Description
AZPosition TELAZ Telescope mount Azimuth
ELPosition TELALT Telescope mount Altitude
S_DGRPosition LDGROT/RDGROT Raw Rotator Angle
MODS uses the raw rotator angle to define various instrument servicer rotations (e.g., for loading masks, servicing cameras, entering the service hatch) etc. via the rotServicePosition() calls in the IIF.

-- DavidThompson - 29 Mar 2010
Converted to external names ChrisBiddick 3 Nov 2016
Topic revision: r7 - 03 Nov 2016, ChrisBiddick
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