[daip] [!7318]: AIPS - MAXFIT and FSHIFT

[Michael Bietenholz]

Michael Bietenholz updated #7318
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MAXFIT and FSHIFT
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           Ticket ID: 7318
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/7318
           Full Name: Michael Bietenholz
               Email: mbieten at yorku.ca
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 25 September 2015 06:35 PM
             Updated: 25 September 2015 06:35 PM
                 Due: 29 September 2015 06:35 PM (4d 0h 0m)
      Resolution Due: 05 October 2015 06:35 PM (10d 0h 0m)



Either I'm confused about what FSHIFT is supposed to be, or the values are wrong:

I tried this:  

1) start with a 256 x 256 image pixel-size = 100 uas.

2) IMMOD to add Gaussian, at FPOS+128.3,129.3
width=5pixels (exact width unimportant)
(FACTOR=0; FLUX=0)

the shift should be 0.3pixels = 33 uas.

I would expect that the required shift (FSHIFT) would be
-33 uas, +33 uas.

3) MAXFIT:

correctly reports a pixel position of the max of 128.29, 129.29
(accurate within 0.01pixel)

However, it says "RASHIFT=  -0.000029 DECSHIFT=   0.000029 to center on pixel"
FSHIFT =  -0.00002949    0.00002949
which corresponds to -106.1598587   106.1598511 uas
so FSHIFT wants to shift it a whole pixel, which doesn't seem right.

(31DEC15; MNJ two days ago)

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