station, umax, vmax, docursor
Plot observed UV points on the UV plane.
EXAMPLE
-------

0> uvplot "BONN"
0>

This example plots the positions of visibilities in the UV plane,
plotting all but the data associated with BONN in green. BONN data
from the first sub-array is plotted in a different color to highlight
it. If the display device has a cursor then interactive mode will be
invoked after the initial display has been completed.

PARAMETERS
----------

station   -   (Optional) The name of a station to highlight in the
              plot. If not given or given as an empty string "", no
              station will initially be highlighted. (Stations
              can be specified subsequently with the cursor).

umax     -    (Optional) Default=0 (0 -specifies the whole range).
              The maximum U coordinate to display.
              The plot will go from -umin to +umin. Unless changed
              with the mapunits command, the units are
              million-wavelengths.

vmax     -    (Optional) Default=0 (0 -specifies the whole range).
              The maximum V coordinate to display.
              The plot will go from -vmin to +vmin. Unless changed
              with the mapunits command, the units are
              million-wavelengths.

docursor  -   (Optional) Default=TRUE.
              If the display device has a cursor but you don't want
              to enter the interactive cursor mode, make this FALSE.

CONTEXT
-------
This task displays the UV coverage of all un-flagged visibilities
selected with the 'select' command. For each baseline, one point is
plotted per IF. Where multiple spectral-line channels are selected
from a given IF, the visibility is the average of those channels and
is displayed at the corresponding mean U and V coordinates.

INTERACTIVE MODE
----------------
If your display device has a cursor, then there are a number of
interactive options that you can use. These are selected by moving the
cursor into the plot window, and pressing the following keys:


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

   L - Re-display the plot.

   Z - Zoom in on a rectangular sub-plot of the displayed region.
       After pressing 'Z' either press 'Z' again to revert to the
       original un-zoomed display, or select the two vertexes of the
       desired sub-plot area by sequentially pressing the 'A' key
       (left-mouse-button) over each. To cancel an incomplete
       selection, press 'D' (middle-mouse-button).

   . - Toggle the marker symbol used to display the data between the
       smallest available and the next largest. By default
       the smallest possible marker symbol is used for speed, but if
       if the data are sparse then the larger marker symbol may be more
       convenient.

   H - (Help) Briefly list all keyboard options.

   n - Highlight visibilities from the next telescope in the currently
       highlighted sub-array. Initially no telescope is highlighted.
       If this key then pressed, the visibilities of the first
       telescope of the first sub-array will be highlighted. Pressing
       this key again highlights the second telescope, etc.. When the
       last telescope of the current sub-array has been plotted, the
       first telescope of the next sub-array will be plotted. So by
       repeatedly pressing this key you will eventually have seen each
       telescope of all sub-arrays individually highlighted.

   p - This has the reverse the effect to the 'n' key, highlighting
       the visibilities of the previous telescope in the current
       sub-array, and wrapping back to the last telescope in the
       previous sub-array, after the first telescope of the current
       sub-array is highlighted.

   N - [Upper-case n] Similar to the lower-case 'n' key this key
       results in the first telescope of the next sub-array in the
       observation to be highlighted. In this way you can jump between
       sub-arrays without having to see all the telescopes of the
       intermediate sub-arrays highlighted one at a time.

   P - [Upper-case p] This has the reverse effect of the 'N' key,
       allowing one to directly step backwards through sub-arrays.

   T - To have a specific telescope of a specific sub-array
       highlighted without having to step through all the intermediate
       telescopes and sub-arrays, press this key. On the text window
       you will then be prompted for the name of the telescope to be
       highlighted. Telescopes are specified by an optional sub-array
       number delimited by a colon, followed by an unambiguous
       telescope name prefix.  If the sub-array number and colon are
       omitted then the sub-array from which telescopes are currently
       being highlighted will be assumed. For instance, both
       3:BONN and BON refer to a telescope named BONN in sub-array 3
       if another telescope of sub-array 3 is currently being
       highlighted. Also, provided that sub-array 2 does not contain
       more than one telescope starting with the prefix JBN, 2:JBN is
       sufficient to refer to a telescope called JBNK1 in sub-array 2.

  S  - This causes uvplot to display details about the visibility
       nearest to the cursor. It shows the sub-array, baseline,
       IF number and date of the visibility.

  C  - This initiates cut area selection, through which a rectangular
       area may be selected within which to flag data. After pressing
       'C' you will be expected to enter the locations of two opposite
       corners of the area, by pressing 'A' (left-mouse-button) over
       the corresponding points of the plot. To cancel a half selected
       area press 'D' (central-mouse-button). Once two corners have
       been selected, all visibilities displayed in that area will be
       flagged and will then disappear from the plot.

  W  - Toggle the scope of edits with respect to spectral-line
       channels. Each point in the plot comes from a single IF, and
       its position in the plot is determined by the mean frequency of
       the channels currently selected from that IF. By default, if
       you select such a point to be flagged, then all spectral-line
       channels of the source IF will be flagged, 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.

  +  - Toggle whether the cursor is shown as a small cross or a
       cross-hair that extends the full width and height of the display.
       Currently only the /xserv and /xwin PGPLOT devices support this
       feature.

OTHER DISPLAY COMMANDS
----------------------
radplot  -   Display visibility amplitude vs. radius.
projplot -   Display visibility amplitude/phase vs. projected UV distance.
vplot    -   Display observed and model visibilities from the current IF.
tplot    -   Display the time-sampling of each telescope of the current IF.
corplot  -   Display the self-cal corrections of the current IF.
cpplot   -   Display observed and model closure phases interactively.
