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MOSSTRONG (Sep2005)     Nordic_Optical_Telescope     MOSSTRONG (Sep2005)



NAME
    mosstrong -- find telescope tweak parameters from two  images  taken
    with  a  mask  and  of  the  object field.  This task allows the two
    images to be binned 2x2 .
    
    
USAGE
    mosstrong  maskimage objectimage
    
    
PARAMETERS
    
    maskimage
        Name of the image taken WITH a mask of  a  calibration  lamp  or
        sky.
    
    objectimage
        Name of the image taken WITHOUT a mask of the target field.
    
    maskcut
        User-defined high cut for colour display. Hidden parameter.
    
    
DESCRIPTION
    This  task  determines  the centroid positions of the fiducial stars
    and the fiducial holes on an image of the mask and an image  of  the
    target  object  field. To measure the pixel coordinates on the image
    the interactive task imexamine is used.
    
    This task allows the two images to be binned 2x2 .
    
    The differences in the measured positions of the stars and the holes
    are  then  transformed  into telescope tweak parameters: offsets and
    rotation. Ask somebody who knows about it (maybe yourself) to  apply
    this  tweak,  which  should  bring  the fiducial stars closer to the
    centre of the fiducial holes of the mask.
    
    
EXAMPLES
    Take an image of the  target  astronomical  field  at  the  required
    telescope  position and rotator angle, and an image of a calibration
    lamp (i.e. halogen) with the mask, and do
    
            mosstrong /data/alfosc/jc240012.fits /data/alfosc/jc240011.fits
    
    Ask yourself to apply the recommended tweak (first the offset,  then
    the  rotation).  This  tweak should bring your fiducial stars closer
    to the centre of the mask holes.
    
    Iterate the tweak by using the task mosstrong until  the  stars  are
    properly positioned in the holes.
    
    
THE INTERACTIVE PART OF THE TASK
    This  task  will  first  display  the  mask image which contains the
    fiducial-star slits/holes.  The user is advised to adjust the colour
    scale  of  the  image  display  such that the fiducial stars AND the
    fiducial holes are clearly visible.
    
    The user has to point the cursor at the fiducial-star slits, and has
    to  press key -a- to activate the centroid algorithm.  If key -a- is
    pressed more than once, the final press  will  be  evaluated.   Each
    press  will  be acknowledged by statistics appearing on the terminal
    that runs IRAF.  To advance to the next slit, press  -q-.   To  stop
    marking slits press -q- WITHOUT pressing -a- first.
    
    Then  the  object  field  image will be displayed, with the fiducial
    stars marked based  on  the  slit  positions  defined  as  described
    above.   Now  the user has to point the cursor at the fiducial stars
    marked by a YELLOW circle, and has to press key -a- to activate  the
    centroid  algorithm.   If  key  -a-  is  pressed more than once, the
    final press will be evaluated.  Each press will be  acknowledged  by
    statistics  appearing on the terminal that runs IRAF.  To advance to
    the next star (slit), press -q-.
    
    On the image display the centroid positions of the slits  and  stars
    will be marked by a RED circle.
    
    When  all  fiducial slits and fiducial stars have been marked by the
    user, the tweak will be computed.  Check the distances between slits
    and stars as output in the IRAF window.  Check that the suggested XY
    and rotational offsets make sense, before applying  the  tweak  with
    mosmove.
    
    If  one  of the centroid positions of the stars or holes seems wrong
    (judging from the RED circles and/or the  computed  distances),  the
    task can be run again with the user discarding the outlying star.
    
    A  good  tweak fit needs no less than 3 stars. Nevertheless, a tweak
    can be computed on only 2 stars.
    
    
TIME REQUIREMENTS
    A lot less than doing it by hand.
    
    
BUGS
    email Jacob W. Clasen (jclasen@not.iac.es),
    for bug reports and constructive remarks
    
    
SEE ALSO
    mosmove, mostweak



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