Documentation on tvclip

Task: tvclip
Purpose: Interactive editing of a UV data set on a TV device.
Categories: calibration, uv-data, tv, plotting, display

     TVCLIP is a MIRIAD task which allows interactive baseline
     editing of a UV data set.  The user should make sure,
     if the display device is capable of creating menus that
     the menu program has been loaded ``before'' running this
     routine (eg. xpanel for the XMTV) - see the User's Guide
     or Cookbook under TV Devices for details.

     When this program is run, each baseline is displayed,
     one at a time, with the x-axis representing channel
     number (increasing to the right), the y-axis representing
     the change in time (increasing upward), and the color
     intensity representing the amplitude or phase (depending
     on the value of the keyword ``mode'') of the visibility.
     The current antenna that constitute the baseline are
     labeled at the bottom of the plot (if room permits).
     In addition, if room permits, a color wedge is displayed
     to the right side of the visibility data and is the sum
     of the data over all displayed channels.  Also, a wedge
     of the sum of the data over all displayed times will
     appear above (or below) the data as room permits.

     The user may edit the data in one of two ways: 1) By
     entering commands at the keyboard; or 2) by selecting
     commands from the listed menu items.  Which method is
     determined by the presence of a menu program (such as
     ``XPANEL'' for the Sun systems).

     If no menu program is currently active, then a message
     is issued to the user and all commands are prompted from
     the keyboard.  Commands are entered followed by a carriage
     return ( CR ).  Single letter abbreviations are used for
     all commands.  The current command list, each corresponding
     abbreviation, and a brief description of each command is
     available by entering a question mark (``?'') as a command.
     Commands requiring further interaction (eg. ``select'' and
     ``value'') will prompt the user when they are invoked.

     If a menu program is active, then TVCLIP will attempt
     to construct an assortment of menu buttons and other
     items that will perform the equivalent of entering commands
     at the keyboard.  Certain commands (eg. ``select'' and
     ``value'') require further cursor input and will prompt
     the user for a particular action (for example: ``select''
     will request the user to select the region to box for
     further flagging commands).

     The current technique of editing is to load the baseline
     to be edited, zoom and pan to the desired location, and
     then, select the region to be edited followed by an
     editing command.  To identify a region to edit, chose
     the ``select'' command (or ``channel'' or ``time'' select
     options) and then use the cursor to box the desired points.
     To select a desired region, move the cursor (mouse) to a
     corner of the region to select; identify, to the program,
     the corner (usually by pushing and holding the left mouse
     button); move the pointer to the other corner (by dragging
     the mouse), and then identify, again to the program, the
     other corner (usually by releasing the left mouse button).
     After the region to edit has been identified, the selected
     region may be flagged as good or bad using the appropriate
     editting command (or button).  If data is flagged improperly,
     the ``undo'' command will reverse the last editing operation.

     NOTE:  If the device does not support this type of ``rubber-
     band'' selection (Eg. XMTV does; MXAS does not), then the
     user will be asked to use the cursor to identify two opposite
     corners to delimit the selected region.

     To save the editing done to a particular baseline, use
     the ``exit'' command (or select the ``exit'' button).
     The flagging changes will be immediately applied to the
     data.  To NOT save the changes made to a particular
     baseline, use the ``quit'' command (or button).  After
     a ``quit'' or ``exit'' operation, the data for the next
     baseline is loaded onto the display and the user may continue
     editing.  Selecting the ``abort'' command (button) at any
     time will perform the same operation as ``quit'', but
     will also terminate the program.

     You can use the 'batch-mode' of tvclip if you have a lot of
     similar flagging to do. Use tvclip in interactive mode to 
     determine a good clip level and a sequence of DIFF and CLIP 
     commands that is appropriate for your data. Then set the 
     clip level and enter the commands in the 'commands' keyword. 
     You can then either watch the automatic flagging on the tv, 
     or switch off the display (options=notv) to speed things up. 

Key: vis
     The name of the input UV data set.  A visibility file name
     must be supplied.  Only one file may be edited at a time.

Key: server
	Standard server keyword. See the help on server for more information.

Key: tvchan
     An integer specifying which TV channel the data is
     displayed.  The default is channel 1.

Key: range
     The minimum and maximum range used in scaling the data
     on the TV.  Default is to autoscale to the first image.
     If this keyword is used, TWO parameters must be input.

Key: tvcorn
     The integer device coordinate of the lower left corner
     of the image.  The default is to center the image on the
     display.  If this keyword is used and only the x coordinate
     value is input, the y coordinate value is set to the x value.

Key: line
	Standard line keyword. See the help on line for more information.
     NOTE: Here ``type'' must be `channel' and the maximum of
     both ``width'' and ``step'' must be 1.  The default is
     to display all channels.

Key: mode
     Display ``amplitude'', ``phase'', ``real'', ``imaginary''.
     By default, ``amplitude'' is selected. For mode=phase, the
     phase is in degrees.

Key: taver
     The length of time (in minutes) used to average the data when
     determining the running mean. This is used with the "DIFF"
     command, where the running mean of the data are subtraced off.
     Two values can be given for taver, being TTOT and TGAP
     respectively. If the time interval between any
     two successive data points is greater than TGAP, or if the
     total time between the first data point in an average
     and any succeeding data point exceeds TTOT, then a new
     average is started.  The default for TTOT is 5 minutes, whereas
     the default TGAP is the value of TTOT.

Key: clip
     The clip level (in average absolute deviations, a parameter 
     similar to rms, but less sensitive to outliers)
     This is used with the "CLIP" command. All data more than clip 
     times the av. abs. dev. from the median will be clipped. 
     This clip operation is repeated until no more points are clipped.
     Common values are 4,5,6. Flagging on stokes V data with clip=4
     usually gets rid of most interference. The default is 5.

Key: options
     - 'nochannel', 'notime' and 'nopixel' are clip options. 
     By default the "CLIP" command will flag channels, times and 
     individual pixels with an rms that is too far from the median. 
     These options allow you to exclude some forms of clipping.
     - 'notv' : display option, do not show anything on the tv.
     Speeds up non-interactive clipping. This can only be used if you 
     also fill in the commands keyword. Because with 'notv' the data 
     does not have to fit on the screen, less time averaging is needed. 
     Usually the data will be flagged at full time resolution.

Key: commands
     This allows non-interactive flagging using the "CLIP" command.
     Use this to specify a sequence of flagging commands to be applied
     for each baseline, e.g., commands=diff,clip. 
     The "EXIT" command is implicitly added at the end of the list.
     You will not be able to interact with tvclip using mouse or
     keyboard if "commands" is set.

Key: select
	Standard select keyword. See the help on select for more information.
     NOTE: The default is to use all visibilities.