Try the code below. It uses routines from the Johns Hopkins
University/Applied Physics Laboratory.
Example:
IDL> TestSL, Longitude, Latitude
Kelly Dean
Fort Collins, Colorado
------------------------------------------------------------ --------
FUNCTION InitColorID
;
; Load discrete color table.
;
tek_color
;
; Match color indices to colors we want to use
;
IF ( !D.N_COLORS GT 256 ) THEN BEGIN
TVLCT, RedTable, GreenTable, BlueTable, /GET
black = ( 256L * BlueTable(0) + GreenTable(0) ) * 256L +
RedTable(0)
white = ( 256L * BlueTable(1) + GreenTable(1) ) * 256L +
RedTable(1)
red = ( 256L * BlueTable(2) + GreenTable(2) ) * 256L +
RedTable(2)
green = ( 256L * BlueTable(3) + GreenTable(3) ) * 256L +
RedTable(3)
dk_blue = ( 256L * BlueTable(4) + GreenTable(4) ) * 256L +
RedTable(4)
lt_blue = ( 256L * BlueTable(5) + GreenTable(5) ) * 256L +
RedTable(5)
six = ( 256L * BlueTable(6) + GreenTable(6) ) * 256L +
RedTable(6)
yellow = ( 256L * BlueTable(7) + GreenTable(7) ) * 256L +
RedTable(7)
ENDIF ELSE BEGIN
black=0 & white=1 & red=2 & green=3 & dk_blue=4 & lt_blue=5 & six=6 &
yellow=7
ENDELSE
ColorID = { ColorID, $ ; Color Index
Black:black, $
White:white, $
Red:red, $
Green:green, $
DkBlue:dk_blue, $
LtBlue:lt_blue, $
Six:six, $
Yellow:Yellow }
RETURN, ColorID
END
;----------------------------------------------------------- -----------
PRO FOV2, longitude, latitude, SatRadius, ColorNum
;
; Procedure FOV2 will determine the maximum field of view
; and draw a circle around the subsatellite point.
;
; Input:
; latitude : Earth latitude of subsatellite point
; longitude : Earth latitude of subsatellite point
; SatRadius : Satellite radius from earth center
; ColorNum : Color number (default : 2)
;
IF ( N_ELEMENTS(ColorNum) EQ 0 ) THEN ColorNum = 2
EarthRadius = 6.371009D6 ; Mean Earth Radius
ScanAngle = ASIN( EarthRadius / SatRadius)
Arc_Dist = !DPI - 1.57080D - ScanAngle
LonLat0 = [longitude, latitude] ; Initial point specified in
radians
lon = FLTarr(37)
lat = FLTarr(37)
FOR lcv = 0, 36 DO BEGIN
Az = lcv * 10.0
Results = LL_ARC_DISTANCE(LonLat0, Arc_Dist, Az, /Degrees)
lon(lcv) = results(0)
lat(lcv) = results(1)
ENDFOR
oPLOT, lon, lat, COLOR=ColorNum
END
;+
; NAME:
PRO SunPlot, Init=Init
;
; PURPOSE:
; Procedure SunPlot will plot the location of the sun on a map.
;
; INPUTS:
; None
;
; KEYWORD PARAMETERS:
; Init - Create sun symbol to be plotted
;
; SIDE EFFECTS:
; Requires public domain IDL routines from JHU
; Assumes that MAP_SET and plotting window are already set.
;
;
; MODIFICATION HISTORY:
; Created by Kelly Dean : December 1997
;-
;
; Load discrete color table.
;
ColorID = InitColorID()
;
IF ( KEYWORD_SET(Init)) THEN BEGIN
;----- Sun Symbol -----------
a = maken(0,360,17)
r = maken(1,1,17)+(1-findgen(17) mod 2)
polrec,r,a,x,y,/deg
usersym,x,y,color=ColorID.yellow,/fill
SunTLE = -1
ENDIF
;-------- Handle time ---------------
dt0 = systime() ; Current time is def.
dt = dt0 ; Copy date/time string.
off = gmt_offsec() ; Find correction from local to UT.
dt_tm_inc, dt, off ; Convert to UT.
dt_tm_brk, dt, dd, tt ; Break input into date and time.
date2ymd, dd, y, m, d ; Break date into y,m,d.
jd = ymd2jd(y,m,d) ; Find Julian Day number.
ut = secstr(tt)/3600. ; Convert time to UT in hours.
;-------- Solar RA/Dec ---------------
sun, y, m, d, ut, app_ra=ra, app_dec=dec, dist=dist
;-------- GMST (Greenwich Mean Sidereal Time) -----
st = lmst(jd,ut/24.,0)*24
;------ Subsolar point ------------
lat = dec
lng = 15.0*(ra-st)
;
; Plot sun's location and terminator
;
plots, lng, lat, psym=8
FOV2, lng, lat, (dist * 1.4956D11), ColorID.yellow
END
;----------------------------------------------------------- ----------
PRO LACMap, lon, lat
;
; Load discrete color table.
;
ColorID = InitColorID()
;
; Set up an orthographic projection centered over the north Atlantic.
; Fill the hemisphere with dark blue.
; Specify black gridlines
;
MAP_SET, /ORTHO, lat, lon, 0, $
/ISOTROPIC, $
/HORIZON, $
E_HORIZON={FILL:1, COLOR:ColorID.dkblue}, $
/NoBorder, $
COLOR=lt_blue
; Fill the continent boundaries with solid white.
MAP_CONTINENTS, /FILL_CONTINENTS, COLOR=ColorID.white
; Overplot coastline data.
MAP_CONTINENTS, /COASTS, COLOR=ColorID.black
; Add rivers, in light blue.
MAP_GRID, LatDel = 15, LonDel = 30, Color = ColorID.black
END
;----------------------------------------------------------- -----------
PRO TestSL, Lon, Lat
; Hint: Color works best when decompose=1
; Hint: Default map location Colorado, USA
IF ( N_ELEMENTS( Lon ) EQ 0 ) THEN Lon = -105.0
IF ( N_ELEMENTS( Lat ) EQ 0 ) THEN Lat = 45.0
WINDOW, 0, XSize=512, YSize=512, TITLE='Sun Location'
LACMAP, Lon, Lat
SUNPLOT, /Init
END
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