Procedure for taking AGw Transformation Data

This is the procedure for collection of AGw Transformation Data with IRTC in order to calibrate the AGw probe coordinates. The data set is a series of IRTC (or possibly LUCI or MODS) images of the on-axis star, at various guide star locations in the field. The initial transform needs about 25 stars. Seeing should be no worse than 0.8 arcsec. A refined transform needs 50 stars in 0.6 arcsec seeing.


Select one of the Stone fields close to the meridian listed in StarCharts. Only these Stone fields with good astrometry and proper motions are useful.

Do it with IDL

All of the IRAF instructions below have been superceded by Doug's automated IDL routine transform_collect .

IRAF instructions below - don't use them.

Use the IRAF transtar script described in JohnSpecial. Script needs some modification for using LUCI images.

Note: ImportantParameters in LBTtoolsIRTC for RFBG/LFBG, especially when you are switching between left and right sides.

Be sure that you are taking IRTC data in H-band. If you want to use J-band, it will be necessary to change LEFTWAVELENGTH/RIGHTWAVELENGTH in the appropriate place in /home/telescope/TCS/Configuration/PCS/PCSInstruments.conf.

Please record the current value of LEFTZEROPOINT/RIGHTZEROPOINT for keeping track of the rotation of the transformation.

For LUCI or MODS, the images should be taken with flexure compensation turned on.

This is the semi-automated procedure using

  • Change to the world-writeable data directory cd /OldRepository/IRTC_Data/20100627/transform

  • Prepare for LBTtools operation with prepdir

  • Send an active preset on-axis to the astrometric field of interest pointto StoneOagw TelMode=ACTIVE gs=0
    • Stop to adjust the pointing if it was off by more than 5 arcsec (you don't want it to drift away later).

  • Let the active optics focus and collimate for a few minutes, until GCS reports rms<400 nm.

  • Move to an off-axis guide star pointto StoneOagw TelMode=ACTIVE gs=21 PA=0

  • Take an IRTC image takeimage 2.0
    • make sure the image is not saturated: < 16000 counts (look at with ds9)
    • if saturated then try 1.0 or 0.5 seconds

  • Set the exposure time and number of frames epar transtar

  • Set the offset parameters to absolute epar offset

  • Offset the telescope to a blank sky position offset 30 0

  • Take a sequence of IRTC images with 30 seconds of integration time to average the seeing takeseq 2.0 15

  • Go back to the nominal pointing offset 0 0
    • Let GCS collimate a couple times

  • Run the script to make multiple calls to cl < home$
transtar (20) irtc.20100101.043226.fits /newdata/
transtar (19) irtc.20100101.043442.fits
transtar (14) irtc.20100101.043653.fits
transtar (16) irtc.20100101.043911.fits
transtar (17) irtc.20100101.044132.fits
transtar (18) irtc.20100101.044406.fits
transtar (5) irtc.20100101.044625.fits
transtar (2) irtc.20100101.044908.fits

Error Recovery

If the script dies then in /home/LBTO/iraf % cp

then edit and remove (comment out) all the transtar(#) that you have already done

Different pre-prepared scripts have different patterns of guidestars at different position angles, etc. A set of scripts organized by position angle exists in /home/LBTO/iraf for several fields including StoneLagw.

A set of semi-scrambled scripts for StoneLagw also exists in /home/LBTO/iraf/

You should record in the log an occasional pair of cube and single images that should be together, so that typographical errors or header problems can be sorted out later.

Quick Look

To check the data, create a Stone0.files, make the file list and run the IDL task irtc_process_set to see that images are OK and reasonable centriods are found (eg if the transformation were perfect, the centroids for all images would be the same. Expect them to be different by a few pixels)

getdat data is in /home/agwuser/agw-control/logbook.1 on agw-control.


(under construction)

Needed information:
  • Centroids of the star images
  • Requested X-Y positions from GCS
  • Actual probe positions and encoder coordinates from the getdat logbook.1 file
  • Position Angle

This is the sequence of steps for collection of the data manually (tedious)

  • Send an active preset to the astrometric field of interest, and let the active optics focus and collimate for a few minutes. pointto M67astrom gs=4 TelM ="ACTIVE" PA=INDEF

  • ssh agwuser@agw-control in an xterm window

  • adjust the IRTC/LUCI/MODS exposure time to get a decent image of the on-axis star without saturating. Set the IRTC data path to r: .

  • Repeat the following sequence for 20-50 off-axis stars in the field. Start with PA=0, but fill out the sample with other PAs to get enough stars.

    • Preset to an off-axis star pointto M67astrom gs=48 TelM ="ACTIVE" PA=0
    • Wait for guiding to settle (typically 10 sec)
    • Take an IRTC/LUCI/MODS data cube that lasts 20-30 second plus a single image takeseq 0.05 200
    • Run Jesper's script on agw-control to record the probe encoder coordinates. ./getdat0 or ./getdat0 star# (substitute the AGw number for 0)
    • Record the time, guidestar number and cube number (or LUCI/MODS image number) in the wiki log (enough redundant information that we can sort out typos)

-- JohnHill - 07 Sep 2010
Topic revision: r7 - 10 Sep 2017, JohnHill
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