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Invert rejecting all visibilities

PostPosted: Wed Jul 05, 2017 4:20 pm
by ncy
Hi,

I have a snapshot observation made with H214 array configuration at cm wavelengths. After usual flagging and calibration, I tried form an mfs continuum image with only ant 6, all visibilities were rejected by invert. uvfstats indicates that only ~20% of data were flagged and uvplt also looks fine. I tried using slop with invert, as suggested by another post in the forum, but failed to work.

Best,
Stephen

Re: Invert rejecting all visibilities

PostPosted: Wed Jul 05, 2017 4:30 pm
by ste616
Hi Stephen,

Can you please post your inputs to invert in full please, and the terminal output?

Re: Invert rejecting all visibilities

PostPosted: Wed Jul 05, 2017 5:58 pm
by ncy
sure.

invert vis=test.uv map=test.imap cell=10 imsize=1025 stokes=i robust=2 select="ant(6)" options=mfs

invert: Revision 1.22, 2016/01/20 03:03:49 UTC

Reading the visibility data ...
Making MFS images
Visibilities accepted: 0
### Warning: Visibilities rejected: 922050
### Fatal Error: No visibilities to map

Re: Invert rejecting all visibilities

PostPosted: Wed Jul 05, 2017 7:01 pm
by ste616
Thanks Stephen. Based on the output, I would first check that antenna 6 is present in the data, because I can't immediately see any problem with the command.

Re: Invert rejecting all visibilities

PostPosted: Wed Jul 05, 2017 8:55 pm
by ncy
I saw the data points when plotting out with uvplt

uvplt vis=test.uv device=/xs select="ant(6)" stokes=i options=nobase

so those are not flagged, but for some reason just rejected by invert. I can send around the data for a closer look if needed.

Re: Invert rejecting all visibilities

PostPosted: Wed Jul 05, 2017 9:17 pm
by ste616
Yes, I think we may need to look at the data. What does the output of that uvplt command look like in PGPLOT?

Re: Invert rejecting all visibilities

PostPosted: Thu Jul 06, 2017 1:29 pm
by ncy
Hi Jamie,

I've attached a few plots, made with the following commands respectively

uvplt vis=test.uv stokes=i select="ant(6)" nxy=3,2 device=plt1.png/png
uvplt vis=test.uv stokes=i select="ant(6)" nxy=3,2 axis=freq,amp options=nofqav device=plt2.png/png
uvplt vis=test.uv stokes=i select="ant(6)" nxy=3,2 axis=uc,vc options=nofqav device=plt3.png/png

Best,
Stephen

Re: Invert rejecting all visibilities

PostPosted: Thu Jul 13, 2017 10:13 am
by Mark.Wieringa
Hi Stephen,

Have you tried a smaller cellsize? Try 1 or 2 and see what happens. It may be that the long baselines are falling of the edge of the uv grid.
On another note, from your uv plot it doesn't look like you have enough data for a 2-d image. Unless test.uv is just a small subset of the data.

Cheers,

Mark

Re: Invert rejecting all visibilities

PostPosted: Thu Jul 13, 2017 1:12 pm
by ncy
Using a small cellsize as suggested works perfectly! Thanks Mark. The observation was a snapshot with very short integration time of a few min only.