Watch out for the STOKES parameter when plotting (even if you don't care about polarization)

When using the many plotting/flagging programs in AIPS, make sure to check the value of the STOKES parameter before plotting (try help stokes to see the options and select the one appropriate for that data set). Different tasks have different STOKES defaults, so sometimes displaying data in one program results in a totally different plot than in another program because one is including some polarizations the other is not. This particularly can be a problem if you have cross-polarization values you don't care about (yet).

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Plot labels and tick marks

Reader René would like to know about some aesthetic issues in plotting:

I have a question regarding labeling. The LTYPE-parameter (eg. in task 'greys') lets you plot "Label in arcsec or other units from reference pixel". This is just what I need, but it stupidly plots it in degrees instead of arcminutes. Is there a way to change this? (Except transforming the coordinates of the whole image I mean ...)

Also is there a way to adjust the number of ticks to plot? (Add minor and major ticks?)

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Multiple contours on one plot

From reader Carl:

Hey I'm bumping this because I have a question regarding contour plots. I'd like to overlay 3 separate contour plots onto each other. The AIPS documentation indicates that it can display plots from multiple images, but is a little ambiguous as to whether it can display the contour plots of both images, or just the contour of one and the greyscale of another. Reading the AIPS help file and playing with the task seem to hint that the latter is the case. I'm just wondering if anyone knows for sure whether this can be done in AIPS, and if so, how. Thanks!

Thanks for the question Carl. See below for my response.

I don't know for sure because I've never tried it, but I'm pretty sure that you can only have one set of contours in KNTR. AIPS plotting is not the most flexible.

Some solutions that might not be great:

1) Use a programming language (Python, IDL, perl, C, fortran, etc) and a fits library to read in your files and then plot them exactly like you want.

2) Make three different contour plots of exactly the same area and overlay them in Illustrator.


Anybody else have some solutions?

I'm wishing that for my latest paper, I'd done custom plots instead of AIPS plots. My hope is that the plotting situation will improve with CASA since it's all plugged into Python and the plotting libraries there.

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Two More Ways to Identify Bad Data

Crystal also said a good way to identify RFI is to look at Stokes V, either in TVFLG or UVPLT or whatever. RFI is usually polarized and will pop out as unusually high baselines/channels/times.

Stokes V will usually mimic your amplitude structure (as a function of baseline length). So, for example, if your source has high amplitudes at short baselines, Stokes V should also be a bit higher on these short baselines (so don't get confused and flag them).

And another way to find that bad data-- Data weights. Plot your data in UVPLT with BPARM = 0 13. The weights for all the data should cluster-- if there are any points that are anomalously low or high, flag them! Crystal says she likes to use WIPER. Obviously, be more concerned about data with really high weights that really low weights-- because this data will affect your overall data set more, as it is up-weighted!

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Need Larger Fonts on Plots

I'm trying to get the labels for my plots in AIPS to be much larger than the default. LWPLA has an option to specify the font size, dparm(8), but after playing with it, it seems like 24pt is the maximum font size. I would really like to use something bigger than this. I can modify the labels manually in Illustrator, but that requires repositioning all the labels, which is way too time intensive. Any other ideas?

UPDATE: Solution using ASPMM parameter in LWPLA detailed in comments.

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Bins in UVPLT

You know what is a great easy way to visualize your data that I often forget about? Bin your data in UVPLT! For example, if you are making a UV distance vs. Amplitude plot, then you can actually see the amplitude structure instead of just seeing tons of points ranging all the way down to an amplitude of zero.

All you have to do is set BPARM(8) = 50 or the number of bins you want.

I think it also plots up faster this way then plotting lots of individual points!
Of course, if what you care about is a handful of really pathelogical points, than this is not the right strategy. But if you are, say, trying to identify a bad baseline or something, this works great!

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I want a *$*%ing beam on my image

This should be easy, but I've totally forgotten how to do it. How do I get the beam displayed on the TV when I'm looking at my image?

On a non-aips note, we had a small earthquake in Socorro last night-- 3.3 mag! It was my first one and I'm very excited about it.

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