PERSPECTIVE

        [GREG2\]PERSPECTIVE [Altitude  Azimuth]  [/FACTOR  Fv  Ov]  [/LOWER]
    [/LINES]   [/STEP  nsx  nsy]  [/AXES  Xmin  Xmax  Ymin  Ymax]  [/CENTER]
    [/VERTICAL Vmin Vmax]

    Makes a parallel projective view of the Regular Grid array, with  hidden
    lines  removed. Altitude and Azimuth are the values of the corresponding
    viewing angles  in  Degrees.  Default  values  are  45  and  45  at  the
    beginning,  and  then  the  last values given.  The upper part is drawn,
    unless the /LOWER option is present.

    Automatic scaling to match approximately the current box is used, but it
    is only a rough guess and may fail if extrema of the Regular Grid occurs
    near the edges. Fine tuning of the plot scale can be obtained using  the
    /FACTOR  option.  It  controls scaling of the Regular Grid values by the
    factor Fv (default 1) and an offset Ov which is in physical units  along
    the Y direction of the plot.

    The Regular Grid array is plotted according to the  orientation  implied
    by command LIMITS, but the whole array is plotted.  The /STEP option may
    be used to indicate to take only 1 pixel over Nsx ones for  the  X  axis
    (resp.  Nsy  and  Y).  The /AXES option plots (X,Y) axes.  The /VERTICAL
    option controls the max, min of plotted perpsective and plots a Z  axis.
    The  /CENTER  option  centers  (?)  the perspective.  BLANKED PIXELS are
    forced to the  minimum  value  of  the  map,  or  the  Vmin  value  when
    the/VERTICAL option is in use.