NAME:
   plotglob
 PURPOSE:
   Plot a globe projection with latitude and longitude lines
 DESCRIPTION:
 CATEGORY:
   Miscellaneous
 CALLING SEQUENCE:
   plotglob,lon,lat,polang
 INPUTS:
   lon    - East longitude of center of disk (degrees)
   lat    - Latitude of center of disk (degrees)
   polang - Position angle of North (CCW from +y, in degrees)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
   BORD     - Flag, if set, put a ticked border around plot.
   DLAT     - Spacing between latitude lines (default=30 degrees)
   DLON     - Spacing between longitude lines (default=30 degrees)
   DP       - Angular step size for plot lines (default=5 degrees)
   COLORS   - 4 element vector that specifies color indicies for
                 various line elements in the plot.  The default
                 is a white line for displays and a black line
                 for postscript output.
              colors[0] - Prime meridian and equator
              colors[1] - 180 deg longitude meridian
              colors[2] - Other grid lines
              colors[3] - Limb
   LINESTYLE - Linestyle for wire grid, default=0
   NOERASE  - Flag, if true, suppresses initial erase of plotting
              area before globe is drawn.  Used for overplotting
              the grid on an image.
   POSITION - Optional 4-element vector that sets location of
              plot on the plotting device (this is a standard PLOT keyword)
   DEVICE   - Flag, if true, means POSITION is in DEVICE units, otherwise,
              POSITION is taken to be in normal units. (standard PLOT
              keyword)
   PAD      - Pad amount in the plot window.  The width of the plot is
              2*(1+pad) where 1 is the radius of the globe.  The default
              value is pad=0.15
   NOLIMB   - Flag, if true, supresses plotting the limb of the globe.
   LATPTS   - Latitude vector of positions to compute X,Y on plot for.
   LONPTS   - Longitude vector of positions to compute X,Y on plot for.
                 Both of LATPTS and LONPTS must be provided and must be the
                 same length.  If this condition is met, then XPTS,YPTS will
                 contain the x,y positions of these lat/lon pairs on the
                 plot.  If the condition is not met then any input through
                 these keywords is silently ignored.
   OFFSET   - Optional offset (x,y) of center of disk in units of disk radius
                 default=0,0

 OUTPUTS:
 KEYWORD OUTPUT PARAMETERS:
   XPTS     - X position of LATPTS/LONPTS input
   YPTS     - Y position of LATPTS/LONPTS input
   ZPTS     - Z position of LATPTS/LONPTS input (positive means it's
                 on the visible part of the globe, negative means it is
                 on the back side).
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
   96/01/26, Written by Marc W. Buie, Lowell Observatory
   96/02/12, MWB, added POSITION and DEVICE keyword support
   96/05/10, MWB, added NOLIMB keyword
   2002/03/15, MWB/Joel Parker, added BORD, LATPTS, LONPTS, XPTS, YPTS
                  keywords.  Also, the /ISOTROPIC keyword is set on the
                  initial plot call.
   2009/01/16, MWB, added LINESTYLE keyword
   2015/11/09, MWB, added OFFSET keyword