[daip] [!7577]: AIPS - IRING

[Eric Greisen]

Eric Greisen updated #7577
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       Staff (Owner): Eric Greisen (was: -- Unassigned --)
              Status: Closed (was: Open)
                 Due: - Cleared - (was: 13 November 2015 06:02 PM)

IRING
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           Ticket ID: 7577
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/7577
           Full Name: Lynn Matthews
               Email: lmatthew at haystack.mit.edu
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Closed
            Priority: Default
      Template Group: Default
             Created: 10 November 2015 06:02 PM
             Updated: 11 November 2015 10:50 PM



The help file about CPARM(6) says
              (6) : 1 => CPARM(1-3) in pixels.  Use this for
                    non-astronomical images although it could be used
                    also for those images that have no Clean beam.
                    The pixel values are assumed independent when
                    computing the errors in the mean.

This means that the Clean beam is ignored and the pixels
are assumed independent.  That is why the Sigmas differ
and the Sum for arc sec converts to Jy and for pixels
does not.

The computation which determines the ring number to assign a pixel
is simple (Radius - cparm(1)) / cparm(2) + 1) which causes pixels exactly
5 (in your case) from the center to go to ring #2.  IMSTAT is not
concerned with rings and so includes pixels exactly 5 away.

There are in fact 12 pixels in a circle of radius 5 that have exactly 5.0
for a radius (x,y) = (5,0), (4,3), (3,4) and 9 similar ones with permuted
signs.

Perhaps the help could be improved a bit.

Eric Greisen




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