uvmin, uvmax
Set the min and max UV radii of usable visibilities for gridding.
EXAMPLE
-------

0>uvrange 0.1,10
Only data in the UV range: 0.1 -> 10 (mega-wavelengths) will be gridded.
0>

The second line is the response from the 'uvrange' command, confirming
the user's selection. To see what the currently assigned range is, type:

0>uvrange
Only data in the UV range: 0.1 -> 10 (mega-wavelengths) will be gridded.
0>

To cancel a previously selected range, type:

0>uvrange 0,0
The full UV range of the data is currently selected for gridding.
0>

PARAMETERS
----------

uvmin - The minimum UV radius from which visibilities will be used
        during gridding. Unless changed with the mapunits command, the
        units are million-wavelengths.

uvmax - The maximum UV radius from which visibilities will be used
        during gridding. Unless changed with the mapunits command, the
        units are million-wavelengths.

If uvmax <= 0 or uvmin < 0 or uvmax < uvmin, no select range is
applied and any previous select range is cancelled.

eg.  'uvrange 0,0'  cancels any previous select range.

Whenever a new UV data set is read with the 'observe' command, any
existing values of uvmin and uvmax are discarded.

CONTEXT
-------
This function effects subsequent invokations of the 'invert' command.
The select range remains in force until this command is called again,
or until a new data-set is read with the 'observe' command.

The range is applied during 'invert', such that all visibilities whose
radial distance in the UV plane exceeds uvmax, or is less that uvmin,
are excluded from gridding, prior to Fourier inverting the map and
beam into the image plane.

SIDE EFFECTS
------------
Use of this command will cause the next 'clean', 'mapplot' etc..
to re-invert the modified UV data-set to produce an updated dirty
beam and residual map.

RELATED COMMANDS
----------------
uvtaper  - Apply a gaussian taper to the gridding weights.
uvweight - Selects combinations of natural,uniform, uncertainty, and
           radial weighting.
uvrange  - Constrain the min and max UV radii within which visibilities
           are gridded.
uvzero   - Set a zero-UV-spacing flux.
