[daip] Bug and gotcha feature in NINER (31DEC18) {External}

[Patrick Leahy]

Hello AIPS - hope that's still Eric:

This is about NINER version 31DEC18 (the only version we have installed at Jodrell Bank). I checked CHANGES.DOC to see if this has been fixed in more recent version, but I don't think so: NINER is only mentioned on item 15763.  April 19, 2022, which doesn't look as if it relates to what we see.

BUG: OPCODE = 'NORT' gives a positive answer if the intensity is increasing from north to south, while OPCODE='SOUT' gives a positive answer if intensity is increasing south to north - these are the wrong way round and not what would be produced by the 3x3 grids shown in the HELP.  I'm guessing that the masks are swapped although I haven't looked into the code.

FEATURE: OPCODE 'EAST' and 'WEST' give the results expected from the masks in HELP (although I think there is a typo in the WEST mask which has a -2 in the RH row where I would expect a -1).
However, these are defined as on a map looking down, not up, i.e. they imply that East is on the right. The NE, SE, SW, NW masks are consistent with this. Rather than changing the code I'd suggest that this was just highlighted in the task description, i.e. add "NB: NINER's compass points are defined with East on the right, i.e. the geographical, not astronomical convention."

A simple test to show this (which we have done) is to run NINER on a PATGN image containing a large Gaussian.

Best wishes,
            Paddy Leahy and Phoebe Ryder



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