[CLEAN\]UV_FLAG
Display UV data and calls the cursor to interactively select a region
where UV data will be flagged. The parameters for the display are as in
UV_SHOW.
Subsequent mapping with UV_MAP will ignore flagged data. Unflagging can
only be done by re-loading the UV data set with command READ UV.
UV data flagged using command UV_FLAG can be saved on file with command
WRITE UV File.