;+
; NAME:
;  locgrid_onespot
; PURPOSE: (one line)
;  Return location arrays for a rectangular projection map
; DESCRIPTION:
;  Return location arrays for a rectangular projection map
; CATEGORY:
;  Volatile Transport
; CALLING SEQUENCE:
;  locgrid_onespot, lat_deg, lon_deg, lat_delta_deg, lon_delta_deg, n_loc, lat, lon, angarea_delta
; INPUTS:
;  lon_deg - center longitude (degress)
;  lat_deg - center latitude (degress)
;  lon_delta_deg - full width in longitude (degrees)
;  lat_delta_deg - full width in latitude (degrees)
; OUTPUTS:
;  n_loc - number of locations (always one).
;  lat - latitude center of each location (radians)
;  lon - longitude center of each location (radians)
;  angarea_delta - angular area of each location (ster)
;
;  n_vert - number of vertices
;  lon_vert - lonitude of vertices
;  lat_vert - latitude of vertices
;  vert[6,n_loc] - indices of vertices
; PROCEDURE
;  The exact area of a latitude band is the area from
;  north pole to the bottom of the band minus the area
;  from the north pole to the top of the band.  This
;  is multiplied by the fraction of longitude coverage.
; MODIFICATION HISTORY:
;  Written 2011 Aug 3, by Leslie Young, SwRI
;  2015 Apr 11, move to grahics IDL library
;-

pro locgrid_onespot, lon_deg, lat_deg, lon_delta_deg, lat_delta_deg, n_loc, lon, lat, angarea_delta, $
                     n_vert, lon_vert, lat_vert, vert

    deg = !dpi/180.d
    n_loc = 1
    lat = reform(lat_deg * deg, 1)
    lon = reform(lon_deg * deg, 1)
    lat_delta = lat_delta_deg * deg
    lon_delta = lon_delta_deg * deg
    angarea_delta = reform( lon_delta* ( sin(lat + lat_delta/2) - sin(lat - lat_delta/2)), 1)

    n_vert = 4
    lon_vert = lon[0] + [-1,1,1,-1] * lon_delta / 2.
    lat_vert = lat[0] + [-1,-1,1,1] * lat_delta / 2.
    vert = replicate(-1,6,n_vert)
    vert[0:3,0] = [0,1,2,3]
    
end