Getting rid of distracting black lines in TVFLG/SPFLG

Have you ever loaded your data into TVFLG or SPFLG and seen what looks like lots of blank times (manifested as horizontal black lines cutting through your data)?

This is because TVFLG/SPFLG is trying to load your data with a time bin that is not a multiple of your integration time. So---the solution is to set DPARM(6)! Set DPARM(6) to your integration time in seconds; e.g., for GMRT data:

DPARM(6) = 16.7

(or, if you have time averaged your data, set it equal to your averaging time).

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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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CVEL bug

I received an email yesterday informing people of a bug in CVEL - that is, if you run CVEL on a data set after SPLIT with an NX table, you are affected! I wanted to post it here in case you're not on the Midnight Job (MNJ) list (which I wasn't). Essentially, CVEL will only shift the first scan to the new velocity axis, while the other scans are not shifted. This bug is explained here. I think the possible fixes are to either run CVEL before SPLIT or to run the midnight job to update your AIPS version and then rerun the new CVEL version on your data.

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CASA guides

Hey! If you're learning CASA, check out this new collection of tips and tutorials that I've been contributing to:
http://casaguides.nrao.edu/

And let me know if you see obvious holes in the documentation there (which is, clearly, still under development).

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Error in PCAL

Here's a question from Akshaya Rane:

I am doing polarization calibration and while trying to run 'pcal', I have encountered the following error. Does this has to do something with qualifiers?

PCAL 3: TOTAL INTENSITIES MUST BE PROVIDED
PCAL 3: Purports to die of UNNATURAL causes

Any thoughts?

I should add that Eric Greisen says that if you spend an hour trying to figure out something in AIPS, and you can't, you should feel free to email him and ask his help.

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AIPS to CASA cheat sheet

So, i've been spending the last couple days learning CASA, and I think the most intuitive way to think about it is in terms of what I would be doing in AIPS. Hence the below table. Most tasks in AIPS have a parallel in CASA, although it's not always a one-to-one transfer.

Update: New and improved as of March 5, 2010:

AIPS	CASA	Purpose
APROPOS	taskhelp	List tasks with a short description of their purposes
BLCAL	blcal	Calculate a baseline-based gain calibration solution
BLCHN	blcal	Calculate a baseline-based bandpass calibration solution
BPASS	bandpass	Calibrate bandpasses
CALIB	gaincal	Calibrate gains (amplitudes and phases)
CLCAL	applycal	Apply calibration to data
COMB	immath	Combine images
CPASS	cpass	Calibrate bandpasses by polynomial fitting
DBCON	concat	Concatenate ''u-v'' datasets
DEFAULT	default	Load a task with default parameters
FILLM	importvla	Import old-format VLA data
FITLD	importuvfits	Import a ''u-v'' dataset which is in FITS format
FITLD	importfits	Import an image which is in FITS format
FITTP	exportuvfits	Write a ''u-v'' dataset to FITS format
FITTP	exportfits	Write an image to FITS format
FRING	---	Calibrate group delays and phase rates.
GETJY	fluxscale	Determine flux densities for other cals
GO	go	Run a task
HELP	help	Display the help page for a task
IMAGR	clean	Image and deconvolve
IMFIT	imfit	Fit gaussian components to an image
IMHEAD	vishead	View header for ''u-v'' data
IMHEAD	imhead	View header for an image
IMLIN	imcontsub	Subtract continuum in image plane
IMLOD	importfits	Import a FITS image
IMSTAT	imstat	Measure statistics on an image
INP	inp	View task parameters
JMFIT	imfit	Fit gaussian components to an image
LISTR	listobs	Print basic data
MCAT	ls	List image data files
MOMNT	immoments	Compute moments from an image
OHGEO	imregrid	Regrids an image onto another image's geometry
PBCOR	immath	Correct an image for the primary beam
PCAL	polcal	Calibrate polarization
POSSM	plotcal	Plot bandpass calibration tables
POSSM	plotms	Plot spectra
PRTAN	listobs	Print antenna locations
PRTAN	plotants	Plot antenna locations
QUACK	flagdata	Remove first integrations from scans
RENAME	mv	Rename an image or dataset
SETJY	setjy	Set flux densities for flux cals
SMOTH	imsmooth	Smooth an image
SNPLT	plotcal	Plot gain calibration tables
SPFLG	viewer	Flag raster image of time v. channel
SPLIT	split	Write out ''u-v'' files for individual sources
TASK	inp	Load a task with current parameters
TGET	tget	Load a task with parameters last used for that task
TVALL	viewer	Display image
TVFLG	viewer	Flag raster image of time v. baseline
UCAT	ls	List ''u-v'' data files
UVFIX	fixvis	Compute ''u'', ''v'', and ''w'' coordinates
UVFLG	flagdata	Flag data
UVLIN	uvcontsub	Subtract continuum from ''u-v'' data
UVLSF	uvcontsub	Subtract continuum from ''u-v'' data
UVPLT	plotms	Plot ''u-v'' data
UVSUB	uvsub	Subtracts model ''u-v'' data from corrected ''u-v'' data
WIPER	plotms	Plot and flag ''u-v'' data
ZAP	rmtables	Delete data files

Do you have a favorite AIPS-to-CASA pair? Disagree with any of the above? Let me know in the comments! I'm still learning.

p.s. I'm supposed to be writing CASA documentation for the beginner (e.g., myself), so I doubt this is the last time I will be seeking feedback.

p.p.s. Why is blogger putting this horrific space before my table? I can't get rid of it and it looks fine in the preview. quack. This tip seemed to get rid of it.

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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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