Interactive Channel/Baseline Flagging - TVFLAG

The task tvflag is akin to the AIPS SPFLG: it displays, on a TV device, one baseline at a time, the amplitude or phase (or amplitude or phase difference from a running average computed over some time). Task tvflag will cycle over the set of baselines present, displaying each one, and giving you the opportunity to flag each baseline.

Task tvflag is the last useful remnant of the ``TV'' suite of software (an old package of display software within Miriad), which uses two X-windows based tools, xmtv and xpanel, for displaying. You will need to start up these tools before using tvflag. To start these, use commands

     % xmtv &
     % xpanel &

in a terminal window of your local workstation (which need not be the machine that you are running tvflag on). To use these, you first have to ensure that you are correctly setup to use X-windows programs - see Chapter 3 for more information on using X-windows. Using xmtv and xpanel is simple enough when you can run them on your local workstation. If you have to run xmtv and xpanel from a compute server (e.g. the situation in Narrabri, when using kaputar via an NT workstation), then there can be problems arising from multiple users attempting to allocate a given TCP/IP port. See Appendix E for more information.

The input parameters to tvflag are pretty straightforward. We mention only the more useful ones:

• vis: The name of the visibility data-set to be flagged.
• server: The TV server parameter. This may seem a rather redundant parameter. It is a parameter of the form

  xmtv@host

  Here host is the host name of the workstation running xmtv and xpanel For example

     server=xmtv@tucana
  

  indicates that xmtv and xpanel are running on the machine tucana. There is no default to this parameter, however a value of xmtv@localhost will be adequate when you are running tvflag, xmtv and xpanel all on the one machine.
• select: The usual visibility data selection parameter. One of tvflag's odd characteristics is in its handling of different polarizations. Task tvflag can deal with only a single polarization per run. If it finds that the input data-set contains several polarizations, it will average these together when forming its display. While unusual, this is moderately useful. Assuming the data-set contains all four linear polarizations,

         select=pol(xx,yy)
  

  will produce a Stokes-I display. On the other hand, no selection (i.e. allowing tvflag to average XX, YY, XY and YX) will produce a quantity which is not physically meaningful, but will still allow you to make a quick check for interference and outliers.
• line: The normal visibility linetype parameter. Task tvflag does not support spectral averaging.
• mode: This determines the quantity to be displayed. Possibilities are amplitude, phase, real and imaginary.
• taver: This gives a time interval used for the running mean calculation when displaying in ``DIFF'' mode (see below). This parameter takes two values, both in minutes. The first gives the maximum amount of time in an averaging interval, whereas the second gives the time gap between records which causes an averaging interval to be ended. The default is 5 minutes for both of these.

Typical inputs are:

TVFLAG
vis=vela.line	Specify visibility dataset
server=xmtv@lupus	Specify TV server
mode=amp	Display amplitude
tvchan	Unset is channel 1 else specify
range	Unset for intensity auto-scale
tvcorn	Unset to centre the image
line	Unset for all channels
taver	Controls the computation of the
	running mean for the DIFF command.

After invoking tvflag, a control panel will pop up and a baseline of data will be displayed on the TV. The display shows channels along the x-direction and time along the y-direction. A gap in time in the data is shown by a dark gap. A wedge is displayed both above and to the right of the data. The top wedge is the data averaged over time, whereas the wedge to the right is the data averaged over the channels.

You now perform flagging operations by pressing ``buttons'' on the control panel. We review the meaning of some of the buttons:

• SELECT, SLCT CHAN and SLCT TIME: The first thing that you will normally do is to select some set of data, with one of the three ``select'' buttons. SELECT selects a rectangular region on the display (i.e. some range of times and channels), whereas SLCT CHAN selects all times for a particular range of channels, and SLCT TIME selects all channels for a particular range of times. After pressing the appropriate ``select'' button,
  • move the mouse so that the cursor is at one corner of the region to be selected,
  • depress the left mouse button,
  • drag the cursor to the other corner of the region to be selected,
  • release the mouse button.
• FLAGOOD and FLAGBAD: Having selected some set of data with the previous commands, this data can be either flagged as good or bad with the FLAGOOD and FLAGBAD buttons respectively.
• UNDO: The undo button causes the last flagging command to be undone and discarded.
• RESCALE: The rescale button changes the display scaling, so that the data occupies the full greyscale or colour range. If you have some bad data which has an extremely high amplitude, for example, you will want to flag this and then rescale the display range so that you can see the detail in the remaining data.
• DIFF: The ``diff'' button causes a running mean to be subtracted off the data.
• EXIT, QUIT and ABORT: The ``exit'' button causes the next baseline to be loaded. The ``quit'' button also causes the next baseline to be loaded, but discards any flagging commands performed on the current baseline. Normally tvflag will terminate when it has gone through all the baselines. It is only at this stage that it applies the flagging operations to the actual data-set. Alternately the ``abort'' button causes tvflag to terminate at any time, and not to apply any of the flagging operations to the data-set.
• LIST: This button lists the flagging operations that have been performed to the current baseline.
• VALUE: This button allows you to find the value of pixels on the display. It is somewhat cumbersome - after pressing the ``value'' button, you move the mouse cursor to the pixel of interest, and press the [F3] function key. You continue to move the cursor and press [F3] until you have exhausted the pixels of interest. Then press [F6] to return back to tvflag's normal mode.

There are other buttons on the control panel - but we do not suggest that you use these. They reproduce (rather crudely) buttons on the TV display window. The useful buttons on the TV display are:

• Panner: Pressing this pops up a window that allows you to pan around the displayed image, and to fiddle the colour lookup table. The panner window that it pops up has one of two states - pan and fiddle.
• Luts: This allows you to select a colour lookup table from a small number of palettes.
• + and -: These allow you to zoom in and out. For mysterious reasons, these buttons are disabled when the Panner window is in the fiddle state.
• Reset: Reset the zooming, the lookup tables, etc.
• Resize: This allows the size of the display window to be toggled between full-screen and a more modest size.
• Quit: Hopefully its use is obvious enough!

One shortcoming of tvflag is that it averages the data in time so that it will fit on the display. Unfortunately full time resolution display cannot be recovered. To display the data at full time resolution, you may need to select the data in chunks (with select=time()).