xcenter, ycenter, minsize, maxsize
Change when and where mapplot plots the clean beam ellipse.

EXAMPLE
-------

  0>beamloc 1.0, 0.0, 0.5
  Mapplot clean beam ellipse center: 1,0. Max size: 0.5.

  0>beamloc -1
  Mapplot will not plot a clean beam ellipse.

PARAMETERS
----------

xcenter   -    The location of the beam center along the X-axis,
               measured in normalized plot coordinates (0 -> 1).
               The initial default is 0.0, the left of the plot.

ycenter   -    The location of the beam center along the Y-axis,
               measured in normalized plot coordinates (0 -> 1).
               The initial default is 0.0, the bottom of the plot.

minsize   -    The minimum allowed fractional extent of the beam ellipse
               with respect to the plot width and height. The beam will
               not be plotted when its size is smaller than this limit.
               The initial default is 0.01.

maxsize   -    The maximum allowed fractional extent of the beam ellipse
               with respect to the plot width and height. The beam will
               not be plotted when its size exceeds this limit.
               The initial default is 0.3.

CONTEXT
-------
When plotting clean maps, mapplot usually plots a filled ellipse
representation of the clean beam in the bottom left corner of the
map. 

For esthetic and practical reasons, it is usually desireable to
prevent the beam ellipse from being plotted when it is either very
small with respect to the size of the plot, or so big that it comes to
dominate or obscure important parts of the plot. The latter is
particularly important when zooming in on fine detail. The 'minsize'
and 'maxsize' arguments allow one to specify the allowable range of
sizes as fractions of the width and height of the plot.

The position at which the center of the beam is plotted can also be
changed via the 'xcenter' and 'ycenter' arguments. Both positions are
specified in normalized plot coordinates, with 0,0 refering to the
bottom left corner and 1,1 refering to the top right corner. If either
'xcenter' or 'ycenter' lies outside the range 0 and 1, then no beam
will be drawn. Otherwise the beam will be positioned at the position
given, with the exception that if the position would place part of the
beam outside the map, it will be moved inwards, suitably spaced from
the edge.

RELATED COMMANDS
----------------
mapplot  -  Display map and beam images.
xyrange  -  Set the boundaries of the sub-image to be displayed in mapplot.
loglevs  -  Set logarithmic levels.
mapcolor -  Select mapplot colormap type and transfer function.
mapfunc  -  Change the transfer function used in mapplot.