;
;  CALLING SEQUENCE:  image=it_disk(img,header[,RADIUS=radius])
;
;  PARAMETERS:   img	is the image array to extract circle from
;  		 header is the .fts header from which to get center info,etc.
;
;  NOTES:	 This function only operates on FITS images with CORRECT
;		 header information.  It will extract a circular region
;	  	 specified by radius info in the header.  If another radius
;	 	 is desired, set the keyword RADIUS equal to desired value.
;		 Function's behavior is unpredictable at radii larger than
;		 image array size.
;
;  RETURN TYPE:  INTARR
;
;  CALLS:	 R_COORD.PRO, IT_GETRAD.PRO
;
;  HISTORY:	 Drafted by Tony Darnell, 20-MAR-97.
;
;

FUNCTION it_disk,image,header,radius=radius

  arrsz=SIZE(image)
  cirarr=MAKE_ARRAY(arrsz(1),arrsz(2),/INT)

  IF NOT KEYWORD_SET(radius) THEN BEGIN
    radius=it_getrad(header)
  END

  hcrpix1=fxpar(header,'CRPIX1')
  IF (!err NE -1) THEN ew_center=hcrpix1
  IF (ew_center LE 0) THEN BEGIN
    cen_err=WIDGET_MESSAGE('The centering info in this header is invalid', $
    /ERROR,TITLE='Bummer')
    cirarr(0,0)=-1
    RETURN,cirarr
  ENDIF

  hcrpix2=fxpar(header,'CRPIX2')
  IF (!err NE -1) THEN ns_center=hcrpix2
  IF (ns_center LE 0) THEN BEGIN
    cen_err=WIDGET_MESSAGE('The centering info in this header is invalid', $
    /ERROR,TITLE='Bummer')
    cirarr(0,0)=-1
    RETURN,cirarr
  ENDIF

  ind=LINDGEN(arrsz(1),arrsz(2))
  center=fltarr(2)
  center(0)=ew_center
  center(1)=ns_center
  disk=r_coord(ind,arrsz(1),center)
  cirarr(where(disk LE radius))=image(where(disk LE radius))

RETURN,cirarr
END