subarray, IF_index
Plot time sampling for each telescope of an observation.
EXAMPLES
--------

1. Displaying telescope sampling on an interactive device.

   0>tplot
   Graphics device/type (? to see list, default /NULL): /xw
   Move the cursor into the plot window and press 'H' for help

   All but the first line of the above is output from tplot.

2. Displaying telescope sampling of all sub-arrays, on a hard-copy
   device. 

   0>dev /ps
   0>tplot
   Page 01: Subarray 1
   Page 02: Subarray 2
   0>

   One page was plotted per sub-array to a postscript file.

3. Displaying telescope sampling of a single selected sub-array, on a
   hard-copy device.

   0>dev /ps
   0>tplot 3
   Page 01: Subarray 3
   0>

   A single page was plotted to a postscript file, showing telescope
   sampling in sub-array 3.

4. Starting the plot from sub-array 1 of IF 2.

   0>tplot 1, 2
   Move the cursor into the plot window and press 'H' for help

ARGUMENTS
---------
subarray    -    Default="" which selects all sub-arrays, starting from 1.
                 To start plotting at a specific sub-array, provide its
                 number here. The first sub-array is number 1. If the
                 output device is a non-interactive (eg. hard-copy)
                 device then only this sub-array will be plotted.

IF_index    -    Default=The index of the first sampled IF.
                 The index of the IF to plot first.

CONTEXT
-------
tplot plots the sampling of all telescopes, using one page per
sub-array and IF. Each telescope is assigned a line parallel to the
time axis of the plot. At the time-stamp of each integration, each
telescope whose visibilities have not been completely deleted is shown
as a dot. In general, each telescope is sampled on a number of
baselines per integration. If the visibilities to all those baselines
are not flagged, then the point is plotted in green. If some are
flagged but at least one is not flagged then orange is used, and if
all visibilities are flagged then the point is plotted either in red
or blue depending on whether the flagging is dominated by visibility
flags or by selfcal correction flags.

Note that what the visibilities that go into determining the flag
status of the plotted points, are those selected with the 'select'
command, rather than all visibilities in the observation.

INTERACTIVE MODE
----------------
If the device that you are plotting on possesses a cursor, then tplot
goes into an interactive mode. In this mode, move the cursor into the
plot area and press one of the following keys:

   H - (Help) Briefly list all keyboard options.

   X - Quit the tplot session, and return to the difmap prompt.

   L - Re-display the plot.

   N - Display the sampling of the next sub-array.

   P - Display the sampling of the previous sub-array.

   ] - Display sampling of the next IF.

   [ - Display sampling of the previous IF.

   T - Prompt for the next sub-array to be plotted. This is then
       entered by its numeric ID, at the keyboard.

   U - Select the time range to be plotted. Initially tplot plots
       sampling over the full range of integration times. To restrict
       the range press U, move the cursor to the start of the new
       range and press A (left mouse button), then move the cursor to
       the end of the required range and press A again. Sampling of
       the current sub-array will be re-plotted within the new range.
       To return to the full time range press U twice in succession.

   B - Break the displayed time range into scans. A scan is defined as
       a block of data, separated from the next block of data by more
       than an hour (this can be changed with the 'scangap' command).
       If there are no gaps this large then no change in plotting will
       result. Otherwise, each scan will be plotted within its own box
       and the gaps between scans will no longer be plotted. Scan mode
       will remain in effect until B is pressed again.

   C - Flag any un-flagged samples within a given area (see below).

   R - Restore any flagged samples within a given area (see below).

   W - Toggle the scope of edits with respect to spectral-line
       channels. Each plotted point comes from a single IF, and
       its displayed flag status is determined from the combined
       status of all the channels currently selected from that IF on
       each baseline of the telescope being sampled. By default, if
       you select such a point to be flagged, then all spectral-line
       channels of the source IF will be flagged for each of the
       effected baselines, irrespective of the channels which actually
       went into making the plot. The alternative is to edit just the
       channels that went into making the plot. The 'W' key toggles
       which of the two options is used, and a mode line above the
       plot describes which option is currently in effect.

   + - This key toggles whether the cursor is shown as a small cross
       or as a cross-hair that extends the full width and height of
       the display. Currently only the /xserve and /xwindow PGPLOT
       devices support this feature.

EDITING
-------
The Clip and Restore keys, 'C 'and 'R' enable you to edit all points
inside a rectangular box selected with the cursor. With the 'C'
option, all visibilities related to the selected stations over the
selected integrations are flagged. Similarly, the 'R' option unflags
all related visibilities in the area. To use these facilities, press
the respective key and then move the cursor to one corner of the
required region and press 'A' (left mouse button). Then move the
cursor to the opposite corner of the required region and again press
'A'. The display will be updated to show the results.

Examples of how one might use this facility include, removing a whole
scan at a time for all telescopes, or flagging a bad station over the
whole time range.

Also see the description of the 'W' toggle, which determines whether
to restrict the edits to the channels that went into making the plot,
or whether to edit all channels of the displayed IF.

RELATED COMMANDS
----------------
scangap  -   Change the time gap used to delimit neighboring scans.
radplot  -   Display visibility amplitude/phase vs. UV radius.
projplot -   Display visibility amplitude/phase vs. projected UV distance.
uvplot   -   Display the sampling of the UV plane.
vplot    -   Display observed and model visibilities from the current IF.
cpplot   -   Display observed and model closure phases interactively.
corplot  -   Display the self-cal corrections of the current IF.
