;+
; NAME:
;	rdybsc4
; PURPOSE:
;	Read the Yale Bright Star Catalogue, 4th ed.
; CATEGORY:
;	Image orientation.
; CALLING SEQUENCE:
;	PRO rdybsc4,n,desig,rtasc,dec,mag, thresh=thresh, path=path
; INPUTS:
;	None.
; OPTIONAL INPUTS:
;	None.
; KEYWORD PARAMETERS:
;	thresh: Specifies the magnitude of the faintest stars desired.
;       path:   Specifies the fully qualified path of the star catalogue
;               file, in case it's not in the default location.
; OUTPUTS:
;	n:      The number of stars returned.
;       desig:  Array of standard designations for all stars returned.
;       rtasc:  Array of right ascensions (deg) "   "    "       "   .
;       dec:      "   "  declinations (deg)     "   "    "       "   .
;       mag:      "   "  magnitudes             "   "    "       "   .
; OPTIONAL OUTPUTS:
;	None.
; COMMON BLOCKS:
;	None.
; SIDE EFFECTS:
;	The star catalog file is read.
; RESTRICTIONS:
;	The star catalog must exist at the specified location.
; PROCEDURE:
;	Straightforward.
; EXAMPLE:
;	
; SEE ALSO:
;	
; MODIFICATION HISTORY:
; 	Written by:	D. van der Schee, May 1993.
;-

PRO rdybsc4,n,desig,rtasc,dec,mag, thresh=thresh, path=path

;program to read in the designation, right ascension, declination, and 
;magnitude of stars fron the ybsc4.dat file
; Added THRESH keyword 94/06/20 DPS
; Modified for DOS 96/03/22 DPS
@isitdos
n = 0
IF N_Elements(path) EQ 0 THEN path=''

IF StrLen(path) GT 0 $
    THEN OpenR, unit, path, /Get_Lun $
    ELSE OPENR, unit, ybscdir+dd+'ybsc4s.dat', /GET_LUN
    
READF,unit,n ;n=number of stars - first line of the file
p1='' & desig=REPLICATE(p1,n)

;right ascention is in hours,mins,secs
p2=0  & rah=REPLICATE(p2,n)
p3=0  & ram=REPLICATE(p3,n)
p4=0. & ras=REPLICATE(p4,n)

;negative or positive declination
p5='' & sign=REPLICATE(p5,n)

;declination in degrees, min, sec
p6=0  & dec=REPLICATE(p6,n)
p7=0  & decmin=REPLICATE(p7,n)
p8=0  & decsec=REPLICATE(p8,n)

p9=0. & mag=REPLICATE(p9,n)

FOR i=0,n-1 DO BEGIN
    READF,unit,p1,p2,p3,p4,p5,p6,p7,p8,p9 $
         ,FORMAT='(A14,2I3,F5.1,1X,A1,I2,2I3,F6.2)'
    desig(i)=p1
    rah(i)=p2
    ram(i)=p3
    ras(i)=p3
    sign(i)=p5
    dec(i)=p6
    decmin(i)=p7
    decsec(i)=p8
    mag(i)=p9
ENDFOR
CLOSE,unit
;conversion to decimal degrees
rtasc = 15.*(rah + (ram + ras/60.)/60.)
dec=dec+(decmin+decsec/60.)/60.
ndec=WHERE(sign EQ '-')
dec(ndec)=-dec(ndec)
FREE_LUN,unit

; Restrict to stars less than a given magnitude
IF KEYWORD_SET(thresh) THEN BEGIN
    sel=WHERE(mag LT thresh,n)
    desig=desig(sel)
    rtasc=rtasc(sel)
    dec=dec(sel)
    mag=mag(sel)
    ENDIF

RETURN
END