Instructions for Collecting Pointing Data and Building a Pointing Model


  • Re-measure mechanical rotator center coords on IRTC if it or AGW has been dismounted/mounted.
  • Take pair of TRACK mode images rotated 180 degrees apart, and record new rotator center: X Y
  • Be sure that azimuth and elevation encoders have been reset at 120 deg and 90 deg.

Data Collection:

  • Turn on pointing logging in PCSGUI and record the filename
  • Use Pointingstars5 routine to determine star list and sequence:
    1. In your working directory on an observer workstation:
      cp ~LBTO/POINTING/* . to copy program files
    2. Be sure to run prepdir in the working directory also.
    3. PointingStars5 is called by script
    4. If Pointingstars5 returns a 999, skip this star and try again later
  • In iraf, run the script gopoint (JohnSpecial)
    • lpar gpoint to set agwNum, exptime, Nimages, active, gdelay, ploop.
    • If you specified ploop+, this script runs until you ^C it, otherwise it does one star.
    • Specifying a logfile makes an easy way to record star numbers and times.
    • You can repeat or return to a specific point in the sequence by specifying the new gridID.
  • Continue with gopoint until you have enough stars.
  • Stop pointing log in PCSGUI

Data Analysis (in progress)

  • Measure pointing star centroids if the data were not collected in GUIDE or ACTIVE mode.
  • Generate new pointing model (D.Thompson)


  • Copy new model to ~telescope/TCS/Configuration/PCS/
  • Update LUCIFER entry for LEFTPOINTINGMODEL in PCSInstrument.conf
  • Re-authorize LUCIFER on IIF GUI to read in new pointing model
  • Test new pointing model by pointing to a few stars or taking an additional set of pointing data.

Pointing Model Tips from Dave

Make sure to start the pointing log on PCS when taking pointing model data!

It is OK to correct the pointing with IE and CA during the run as the pointing log uses the mount AZEL directly. If you need to tweak the collimation, it is probably OK to do it all with M1, but I typically only need to manually tweak the focus a little if things are stable.

A "minimum" dataset consists of the first 12 cells, from which I can make a decent pointing model (<6 arcsec rms I would guess). The next 16 fill in between the first 12, then the next 24 fill in more between the first 28, and the final 36 complete the pattern. The full cell list has 88 positions, so if you take pointing data, take sets of 12, 28, 52, or 88 points. If you are diligent, you can take ~25 data points per hour with LUCIFER.

More details on Marco's pointing star program

Marco has set up a script for selecting optimally distributed pointing stars. It lives in /home/LBTO/POINTING

You run it by copying it to a local scratch directory and saying: ./Pointingstars5

The program waits for you to input the "cell" number, just start with 1 and increment each step.
For example, I just ran it and it returns:

66 WT10_355 03 45 27.557 +47 39 37.25 0.00210 -.02700

The "1" is what you type (cell number), the next line is the star info (cell number, ID, RADEC, pmRADEC). The program has the full WT10 and ACT catalogs in it, it will give you the star closest to the middle of the requested cell. You then do a "pointto WT10_355" and get the star on the detector (acquisition camera is OK) with a spiral search if necessary. Once there, take a short exposure and note the image number so I can pull the UT out of the image header to match to the pointing log file. It would be good to take all of the data with the acquisition camera at a PA of close to zero (makes my job easier later), so LUCIFER will need to be at 180.3. If you can use LUCIFER, then PA=0 of course.

If there is no star, the program returns cell number 999 and the coordinates for the center of the cell. Just skip it and try again later. The starting position of the Pointing Model Acquisition is at NE, so ask the OSA to put the AZ at ~ +400 degrees. The cells are distributed such that if you will not have to unwrap the AZ during the scan of the entire AZ range, although it is not a problem for the pointing model if you unwrap in the middle.

-- JohnHill - 15 Jun 2008 -- DougMiller - 26 Oct 2009
Topic revision: r5 - 25 Sep 2010, MarcoPedani
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