Finding Nearest LBT Catalog Stars / Tweaking the Pointing

By: Steve Allanson (LBTO)
Latest Version: 5.14

This is a GUI version of the terminal based script. This is vastly cleaner and easier to use. I have added an option to specify an AZ/EL which I think is very handy when choosing initial pointing stars or generating pointing models. You can choose from any of the available catalogs as displayed in the 'Which?' frame. Any future additions can be easily added. Also, I've added an IE/CA paddle, which makes it very easy to tweak the pointing when required. There is a Spiral option, which visually shows you the state of the pattern, and has the ability to undo steps. You can also create catalog targets on-the-fly for use with IRAF.

    • on any obs machine:
    • cd /home/telescope/sallanson/pointnear/
    • ./pngui &

Catalog Search Tab

  • pointnear catalog tab v4.7:

    • Where?
      • Here - finds nearest catalog stars from current RA/DEC
      • RA/DEC - specify an RA/DEC, finds stars near there
      • AZ/EL - specify an AZ/EL, finds stars near there
    • Which?
      • All available catalogs are listed. Choose which ones you would like to query.
      • Note: these depend on Doug Miller maintaining the xephem catalogs in /lbt/catalogs/xephem/
    • SEARCH - run the tool
    • Finder Chart - Copy/Paste or type a target name from the list, then hit Enter or click 'Show' to display the .jpg
      • Box will turn red if file cannot be found. Check spelling (trailing whitespace is ignored)
      • This replicates Dave's (or Doug's?) 'showFC' iraf package.

Note that any formatting errors in the RA/DEC/AZ/EL boxes will cause the box to turn pink indicating the source of the error. Notice the formatting in the boxes when the 'Here' option is selected.

Plots Tab

  • pointnear plots tab v4.1:

  • These plots correspond to the coordinates that were last queried on the Catalog Tab.
  • They show the AZ/EL tracks from Sunset to Sunrise.
    • plot date changes at local noon (you can use it in the evening to see upcoming targets).
  • A vertical dashed line denotes the current time and AZ/EL position
  • You can click-drag a box around your desired region of interest to zoom in.
    • zoom in far enough to see individual points. You can hover over them to get coordinate values, at 1minute resolution.

IE/CA Paddle Tab

This software 'paddle' aids in moving the star on the Acquisition image in GCSGUI. Parallactic mode is no longer required, as the paddle auto-rotates based on the relative angle between position angle and parallactic angle.

  • pointnear paddle tab v2.0:

    • The buttons and arrows rotate to represent the direction that IE/CA will move the star.
    • NOTE that the paddle is auto-disabled for any focal stations other than directGregorian, bentGregorianFront, bentGregorianBack.
      • It is only enabled for focal stations with rotators and AGw's (EXCEPT LBTI. See below).
    • Option: This is a generic option which invokes a different setup. Currently, this is only employed for LBTI. See below.
    • Lock: This locks the paddle from accidental usage. Toggle when ready to use / finished using the paddle.
    • Both: While you are only shown the paddle for one side, you may wish to apply the same change in IE/CA to the other side at the same time.
  • STEP
    • This is the step-size each button click will change the IE/CA values.
    • It is a slider, in that you click-hold to drag it up/down.
    • You have 2 options:
      • Coarse - 1"-20" step size
      • Fine - 0.1"-1" step size
    • Choose which side of the telescope you want to change, LEFT/RIGHT
    • The INSTRUMENT @ FOCALSTATION is displayed
    • The PA/PAR, and relative angle are displayed
    • Choose whether you want to use the Paddle, or if you want to edit IE/CA manually.
      • In PADDLE mode, the manual mod buttons and PTRESET buttons are disabled, only the paddle will change IE/CA
      • In MANUAL mode, the paddle is disabled, and you can edit the IE/CA text boxed.
        • Click mod to change the IE/CA
    • REFRESH button re-queries the data-dictionary for all the necessary information.
      • BE SURE to click this before making changes so that you have the most up-to-date information displayed
    • PTRESET button performs a ptreset on the chosen side.
      • Note that this is only available in MANUAL mode

  • pointnear paddle tab v2.4 (LBTI):
    • When LBTI is used, the IE/CA paddle locks in the correct orientation for moving the star on CCD47
      • This involves a mirroring (of the usual AGw orientation) and a rotation of +/-90degrees
    • When OPTION is checked, the IE/CA paddle locks to the correct orientation for move the star on the Science Camera
      • This would appear identical to parallactic mode on a gregorian AGw.

    • Similarly, when LINC is used, the IE/CA paddle locks in the correct orientation for moving the star on their Patrol Camera
      • This involves a mirroring (of the usual AGw orientation) and a rotation of -18deg(left) and +5deg(right)


This is a reconstructed version of John Hill's I have adapted it to Perl/Tk, and added some functionality

  • pointnear spiral tab v3.3:

  • Settings/Details
    • Pick which side you'd like to spiral - Left, Right, or Both
    • Settings - pitch (arcseconds), # of half loops, and time delay between iterations.
      • In general, the following pitch settings tend to maximize search grid:
        • LBTI: 7"; MODS: 40"; LUCI: 20"
      • Default Settings button exists to revert back
    • Start/Current IE/CA - This will help you monitor progress.

  • How to run:
    • Click Spiral, no settings changes can be made until completed
    • The Spiral Progress plot will display the current state at each ptincrement.
    • Click Pause when you're ready

  • pointnear spiral tab v3.3:

  • Post-Spiral Options
    • Undo - you can undo the steps all the way back to the start if desired. This is handy for when you accidentaly overshoot.
    • Revert - If you are unhappy with the spiral and wish to go back to the starting IE/CA, use this button.
    • OK! Clear - If you're happy with everything, click this to reset the spiral screen.


Use this tab to create catalog entries on-the-fly, for use with iraf.

This tool takes a user-input RA DEC, then utilizes Tom Sargent's 'gsfinder' to query NOMAD for available guide stars in that field. It then formats it properly for use with Dave Thompson's iraf packages, like 'newpoint' and 'showcat'. Object names are created automatically, and are intended to be unique. I have chose to use OSA as the prefix, as this will primarily be used by the OSAs.

  • Catalog entries created by this tool live in /lbt/catalogs/Scratch/OSA/catalogs/
  • The guide star list is limited to a radius of 5.5' from field center. This radius may be too large in some instances, so take notice.
  • The list is also limited to Rmag<16.0, Coord_err<100, and proper motions <100mas/yr, as previously done by Doug M.
  • If a star is found within <err>" of the RA/DEC you've input, the script assumes that is what you meant. Otherwise, it creates a 'fake' target for id0, with Rmag=0.000.

How To Create a Catalog Entry
  • Input an RA (formatted as and a DEC (formatted as \
  • Set the input 'error' - Nominally 5", this is the allowable distance between input coordinates and the nearest object in the NOMAD results. If the nearest object is within this distance, then it is assumed to be the intended target.
    • The output will be on the right. Review it before proceeding
  • If you're happy with the output, click the SAVE button to commit the entry to the catalogs directory
  • You can now send a preset from IRAF to the object name displayed at the top of the header in the 'Output' section.
  • Click RESET to clear everything on the tab and start over, otherwise click RETRY to keep the input fields intact

Notable Warning Scenarios
  • If the closest star found from the NOMAD query is not within the <err> value defined, the Target ID 0 line is faked.
    • A warning message will be displayed:

  • If the on-axis star is found, but the R_mag is 30.00 in NOMAD, this value is effectively N/A.
    • I force the 30.00 to 0.000 so that GCS does not barf on this extremely faint magnitude
    • A warning is displayed:
-- %USERSIG{SteveAllanson - 2014-06-28}%

-- %USERSIG{SteveAllanson - 2015-05-27}%

OLD Terminal Based Script

This is a small script that compares the current RA/DEC to the pointing stars from (now using the newly formatted catalogs), and calculates the arclength between the two points:

From spherical trig,
cos(d) = cos(90-DEC1)cos(90-DEC2) + sin(90-DEC1)sin(90-DEC2)cos(RA1-RA2)
  • where d is the arclength between objects 1 and 2.

The script weeds out Stone, NGC, and Messier objects from the search.

This script currently executes from Steve Allanson's scratch directory on obs1:
  • ssh into obs1 if you're not currently there.
  • cd /scratch/sallanson/pointnear

To execute,
  • type perl
    • this will give you the nearest 5 objects to the current RA/DEC.

If you're looking for more or fewer results, you can use the optional command line argument:
  • type perl N where N is the number of results you'd like
    • This is the lazy way to find targets of a specific type. One could also request a large number, then pipe the output to grep for a specific type (BS, ACT, WT10 etc.).

You can also specify your own RA DEC if you'd like. You can even choose N results, as long as N is your first argument (but this is not necessary)
  • type perl RA DEC to specify an RA DEC, with default 5 results.
  • type perl N RA DEC to specify an RA DEC, with any number of results.
    • FORMAT: RA must be hh:mm:ss(.ss) and DEC must be dd:mm:ss(.ss). The important thing is the colon. It should complain if you feed it a bad data format.

I've also set up a feature that selects high elevation pointing stars at an azimuth nearby to the current AZ. This is helpful at the beginning of the night when we want to check pointing but not have to wait forever for the AZ slew. As before, you can also specify the number of results. You can also further specify the AZ and EL limits to search.
  • type perl H the actual letter H, for High star. defaults within +/-30deg AZ, and above EL 75.
  • type perl N H where N is the number of results you'd like, as before
  • type perl H AZ where AZ is the +/- in degrees away from your current AZ you'd like to search
    • if you don't care about waiting, perl H 180 will give you all stars closest to zenith.
  • type perl H AZ EL where EL is the elevation in degrees you'd like to search above.
  • The options in the previous two examples could also be prepended with N desired results.

This would ideally be used with Dave Thompson's pointto iraf script. See Sending Presets in IRAF.

-- SteveAllanson - 13 Oct 2010
Topic attachments
I Attachment Action Size Date Who Comment
pngui2.0cat.pngpng pngui2.0cat.png manage 16 K 26 Mar 2012 - 08:14 SteveAllanson pointnear catalog tab v2.0
pngui2.0pt.pngpng pngui2.0pt.png manage 14 K 26 Mar 2012 - 10:56 SteveAllanson pointnear paddle tab v2.0
pngui4.1cat.pngpng pngui4.1cat.png manage 32 K 11 Jul 2013 - 18:01 SteveAllanson pointnear catalog tab v4.1
pngui4.1plots.pngpng pngui4.1plots.png manage 23 K 11 Jul 2013 - 18:18 SteveAllanson pointnear plots tab v4.1
pngui4.7cat.pngpng pngui4.7cat.png manage 33 K 09 Apr 2014 - 09:43 SteveAllanson pointnear catalog tab v4.7
pnguiv1.1.pngpng pnguiv1.1.png manage 16 K 28 Oct 2011 - 07:20 SteveAllanson pointnear GUI v1.1
pnguiv2.1pointLBTI.pngpng pnguiv2.1pointLBTI.png manage 13 K 12 Apr 2012 - 07:29 SteveAllanson pointnear paddle tab v2.1 (LBTI)
pnguiv2.4pt.pngpng pnguiv2.4pt.png manage 14 K 22 Sep 2012 - 11:31 SteveAllanson pointnear paddle tab v2.4 (LBTI)
pnguiv3.3prespiral.pngpng pnguiv3.3prespiral.png manage 12 K 02 Nov 2012 - 14:04 SteveAllanson pointnear spiral tab v3.3
pnguiv3.3spiral.pngpng pnguiv3.3spiral.png manage 13 K 02 Nov 2012 - 14:04 SteveAllanson pointnear spiral tab v3.3
Topic revision: r26 - 02 Jan 2017, SteveAllanson
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