idlastro / Astronomical Utilities: AITOFF_GRID

[Source code]

NAME
AITOFF_GRID
PURPOSE
Produce an overlay of latitude and longitude lines over a plot or image
EXPLANATION
The grid is plotted on the current graphics device. AITOFF_GRID 
assumes that the ouput plot coordinates span the x-range of 
-180 to 180 and the y-range goes from -90 to 90.
CALLING SEQUENCE
AITOFF_GRID [,DLONG,DLAT, LABEL=, /NEW, CHARTHICK=, CHARSIZE=, 
              FONT=, _EXTRA=]
OPTIONAL INPUTS
DLONG   = Optional input longitude line spacing in degrees. If left
          out, defaults to 30.
DLAT    = Optional input latitude line spacing in degrees. If left
          out, defaults to 30.
OPTIONAL INPUT KEYWORDS
LABEL           = Optional keyword specifying that the latitude and
                  longitude lines on the prime meridian and the
                  equator should be labeled in degrees. If LABELS is
                  given a value of 2, i.e. LABELS=2, then the longitude
                  labels will be in hours instead of degrees.
 CHARSIZE       = If /LABEL is set, then CHARSIZE specifies the size
                  of the label characters (passed to XYOUTS)
 CHARTHICK     =  If /LABEL is set, then CHARTHICK specifies the 
                  thickness of the label characters (passed to XYOUTS)
FONT          =   scalar font graphics keyword (-1,0 or 1) for text
/NEW          =   If this keyword is set, then AITOFF_GRID will create
                  a new plot grid, rather than overlay an existing plot.
Any valid keyword to OPLOT such as COLOR, LINESTYLE, THICK can be 
passed to AITOFF_GRID (though the _EXTRA facility) to to specify the
color, style, or thickness of the grid lines.
OUTPUTS
Draws grid lines on current graphics device.
EXAMPLE
Create a labeled Aitoff grid of the Galaxy, and overlay stars at 
specified Galactic longitudes, glong and latitudes, glat
IDL> aitoff_grid,/label,/new        ;Create labeled grid
IDL> aitoff, glong, glat, x,y      ;Convert to X,Y coordinates
IDL> plots,x,y,psym=2              ;Overlay "star" positions
PROCEDURES USED
AITOFF
NOTES
If labeling in hours (LABEL=2) then the longitude spacing should be
a multiple of 15 degrees
AUTHOR AND MODIFICATIONS
J. Bloch        1.2     6/2/91
Converted to IDL V5.0   W. Landsman   September 1997
Create default plotting coords, if needed   W. Landsman  August 2000
Added _EXTRA, CHARTHICK, CHARSIZE keywords  W. Landsman  March 2001
Several tweaks, plot only hours not minutes W. Landsman January 2002
Allow FONT keyword to be passed to XYOUTS.  T. Robishaw Apr. 2006