;+
; NAME: V_RHIJN
;	
; PURPOSE:
;	To calulate a van Rhijn layer.
;
; CATEGORY:
;	
; CALLING SEQUENCE:
;       RESULT=V_RHIJN(EMIS_HT,YY,MM,DD,CAM,FLT [,SMALL=SMALL,SITE=SITE ])
;
; INPUTS:
;       EMIS_HT: The height in km , of the emmitting layer, that the van Rhijn 
;                correction will be applied to.
;
;       YY: The year the image that the van Rhijn correction will be applied to
;           was produced.
;
;       MM: The month the image ...
;
;       DD: The date the image ...
; 
;       CAM: The camera that produced the image ...
;
;       FLT: The filter that produced the image ...
;
; KEYWORD PARAMETERS:
;       SMALL: If set a 256 by 256 image will be expected, otherwise the image
;              must be 512 by 512.
;
;       SITE: Set the site that the camera was at, when it produced the image.
;             If it is not set, then site 3 (Eureka) will be chosen.
;
; OUTPUTS:
;	RESULT: A van Rhijn layer, contianed in a floating point array, of the
;               same size as the image.
;
; COMMON BLOCKS:
;       None.
;
; SIDE EFFECTS:
;       None.
;
; RESTRICTIONS:
;       None known.
;
; PROCEDURE:
;       ...
;
; MODIFICATION HISTORY:
;       Written July 1994, by T A Oliynyk.	
;-

FUNCTION v_rhijn,emis_ht,yy,mm,dd,cam,flt,small=small,site=site

IF NOT KEYWORD_SET(site) THEN site=3

IF KEYWORD_SET(small) THEN BEGIN
   edge=256 
   small=1
ENDIF ELSE BEGIN
   edge=512
   small=0
ENDELSE

col=INDGEN(edge)#REPLICATE(1,1,edge)
row=TRANSPOSE(col)

cr2az,yy,mm,dd,cam,flt,col,row,az,za,small=small,site=site
vr=vanrhijn(za,emis_ht)

RETURN,vr
END