[daip] [!11812]: AIPS - I don't get what UVCRS is doing - its finding some crossings but not others

[Michael Bietenholz]

Michael Bietenholz updated #11812
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I don't get what UVCRS is doing - its finding some crossings but not others
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           Ticket ID: 11812
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/11812
                Name: Michael Bietenholz
       Email address: 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: 21 March 2018 09:53 PM
             Updated: 21 March 2018 09:53 PM
           Reply due: 23 March 2018 09:54 PM (2d 0h 0m)
      Resolution due: 15 December 2020 12:00 AM (999d 2h 6m)

I don't get what UVCRS is doing - am I missing something obvious?  I ran it on the little test data-set attached, and itfound one crossing (or rather near approach) between two baselines but not another, nearer one.(31DEC18 AIPS, midnight job a couple of days ago)I ran UVCRS with APARM = 12 12 1 1 0; STOK  'RR' ; ANTENNAS 0so I'm expecting it to find baseline pairs that come within 12 Mlambda of each other in the uv-plane.It finds only one crossingUVCRS1:  Ellipse with half axes 12.0 x 12.0 MegalamdaUVCRS1:  Number of possible crossings =     4UVCRS1:     1   1   2-  5 /  2-  8  1.869Here are the 4 possible vis in my tset data set - here's the UVPRT output:           Time       Ant    U(Kilo )   V(Kilo )   W(Kilo )   Amp  Phas  Wt1  0/14:45:17.5  2- 5   12526.53  -29544.46   33484.21   4.456  -5 0.24022  0/14:45:17.5  2- 8   26670.29  -20700.05   26666.72   6.675  -4 0.13363  0/16:31:56.6  2- 5   22841.15  -31471.54   25272.92  3.571  -4 0.20554  0/16:31:56.8  2- 8   33388.70  -23948.15   12745.59   5.549  -4 0.1133Of those, the ones on lines 2,3  indeed have a difference in u-v positions of < 12 Mlambda, while the other pairs are > 12 Mlambda, and accordingly UVCRS prints out one crossing, .   So far, its doing as I expect.However, that data also contains a rather closer pair of vis -  only 5.6 Mlambda apart - why is UVCRS not picking these up?          Time       Ant    U(Kilo )   V(Kilo )   W(Kilo )   Amp  Phas  Wt5  0/16:31:55.9  3- 6   87363.98  -12503.98  -85229.07   1.783   4 0.10786  0/16:31:58.7  5- 7   81823.39  -11645.47   -5923.63   4.349  -1 0.1034I thought maybe that the uv-ellipses for the first ones actually cross while those for 3-6 and 5-7 just approach, but as far as I can tell they latter ellipses *do* cross.  Does the w-coordinate somehow matter?

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