POLYGON

        [GREG2\]POLYGON [(File)Name] [/PLOT] [/VARIABLE] [/FILL [Colour]]

    If no argument and no option, it calls the interactive cursor to  define
    the  polygon  summits.   Type any key to go to next summit, D to correct
    the last one and type E to end the polygon definition. The last  polygon
    side  will  then appear. The polygon definition may be aborted by typing
    Q. For X11 displays, you may use the mouse  buttons  for  the  commands.
    The  left  mouse  button draws a vertex, the middle mouse button deletes
    the  last  vertex,  and   the  right  mouse  button  ends  the   polygon
    definition.

    The drawing of the polygon is not stored in the plot, and will disappear
    if  you refresh the plot. The polygon values are stored internally; they
    can be printed with the command GREG1\WRITE POLYGON, and they correspond
    to  the  variables POLY$NXY (number of vertexes), POLY$X and POLY$Y (the
    corresponding coordinates). The currently defined POLYGON is used by the
    commands MEAN and MASK.

    If a Name is given as argument, the cursor is not called but the  summit
    coordinates are read from the corresponding file (X is in column 1, Y in
    column 2), or corresponding SIC Variable if the option /VARIABLE is also
    present.

    If you specify the option /PLOT, the current polygon will be plotted  as
    real  vectors  in the plot, and no longer as temporary vectors as above.
    Option /FILL [Colour] will fill the current polygon, with the current or
    specified colour.