PRO FXREAD, FILENAME, DATA, HEADER, P1, P2, P3, P4, P5, $ NANVALUE=NANVALUE, PROMPT=PROMPT, AVERAGE=AVERAGE, $ YSTEP=Y_STEP, NOSCALE=NOSCALE, NOUPDATE=NOUPDATE, $ ERRMSG=ERRMSG, NODATA=NODATA, COMPRESS = COMPRESS, $ EXTENSION=EXTENSION0 ;+ ; NAME: ; FXREAD ; Purpose : ; Read basic FITS files. ; Explanation : ; Read an image array from a disk FITS file. Optionally allows the ; user to read in only a subarray and/or every Nth pixel. ; Use : ; FXREAD, FILENAME, DATA [, HEADER [, I1, I2 [, J1, J2 ]] [, STEP]] ; Inputs : ; FILENAME = String containing the name of the file to be read. ; Opt. Inputs : ; I1,I2 = Data range to read in the first dimension. If passed, then ; HEADER must also be passed. If not passed, or set to -1,-1, ; then the entire range is read. ; J1,J2 = Data range to read in the second dimension. If passed, then ; HEADER and I1,J2 must also be passed. If not passed, or set ; to -1,-1, then the entire range is read. ; STEP = Step size to use in reading the data. If passed, then ; HEADER must also be passed. Default value is 1. Ignored if ; less than 1. ; Outputs : ; DATA = Data array to be read from the file. ; Opt. Outputs: ; HEADER = String array containing the header for the FITS file. ; Keywords : ; /COMPRESS - If this keyword is set and non-zero, then then treat ; the file as gzip compressed. By default FXREAD assumes ; the file is gzip compressed if it ends in ".gz" ; NANVALUE = Value signalling data dropout. All points corresponding to ; IEEE NaN (not-a-number) are set to this value. Ignored ; unless DATA is of type float or double-precision. ; EXTENSION = FITS extension. It can be a scalar integer, ; indicating the extension number (extension number 0 ; is the primary HDU). It can also be a scalar string, ; indicating the extension name (EXTNAME keyword). ; Default: 0 (primary HDU) ; PROMPT = If set, then the optional parameters are prompted for at the ; keyboard. ; AVERAGE = If set, then the array size is reduced by averaging pixels ; together rather than by subselecting pixels. Ignored unless ; STEP is nontrivial. Note: this is much slower. ; YSTEP = If passed, then STEP is the step size in the 1st dimension, ; and YSTEP is the step size in the 2nd dimension. Otherwise, ; STEP applies to both directions. ; NOSCALE = If set, then the output data will not be scaled using the ; optional BSCALE and BZERO keywords in the FITS header. ; Default is to scale, if and only if BSCALE and BZERO are ; present and nontrivial. ; NOUPDATE = If set, then the optional BSCALE and BZERO keywords in the ; optional HEADER array will not be changed. The default is ; to reset these keywords to BSCALE=1, BZERO=0. Ignored if ; NOSCALE is set. ; ERRMSG = If defined and passed, then any error messages will be ; returned to the user in this parameter rather than ; depending on the MESSAGE routine in IDL. If no errors are ; encountered, then a null string is returned. In order to ; use this feature, ERRMSG must be defined first, e.g. ; ; ERRMSG = '' ; FXREAD, ERRMSG=ERRMSG, ... ; IF ERRMSG NE '' THEN ... ; NODATA = If set, then the array is not read in, but the ; primary header is read. ; ; Calls : ; GET_DATE, FXADDPAR, FXHREAD, FXPAR, WHERENAN ; Common : ; None. ; Restrictions: ; Groups are not supported. ; ; The optional parameters I1, I2, and STEP only work with one or ; two-dimensional arrays. J1 and J2 only work with two-dimensional ; arrays. ; ; Use of the AVERAGE keyword is not compatible with arrays with missing ; pixels. ; ; Side effects: ; If the keywords BSCALE and BZERO are present in the FITS header, and ; have non-trivial values, then the returned array DATA is formed by the ; equation ; ; DATA = BSCALE*original + BZERO ; ; However, this behavior can overridden by using the /NOSCALE keyword. ; ; If the data is scaled, then the optional HEADER array is changed so ; that BSCALE=1 and BZERO=0. This is so that these scaling parameters ; are not applied to the data a second time by another routine. Also, ; history records are added storing the original values of these ; constants. Note that only the returned array is modified--the header ; in the FITS file itself is untouched. ; ; If the /NOUPDATE keyword is set, however, then the BSCALE and BZERO ; keywords are not changed. It is then the user's responsibility to ; ensure that these parameters are not reapplied to the data. In ; particular, these keywords should not be present in any header when ; writing another FITS file, unless the user wants their values to be ; applied when the file is read back in. Otherwise, FITS readers will ; read in the wrong values for the data array. ; ; Category : ; Data Handling, I/O, FITS, Generic. ; Prev. Hist. : ; W. Thompson, May 1992, based in part on READFITS by W. Landsman, and ; STSUB by M. Greason and K. Venkatakrishna. ; W. Thompson, Jun 1992, added code to interpret BSCALE and BZERO ; records, and added NOSCALE and NOUPDATE ; keywords. ; W. Thompson, Aug 1992, changed to call FXHREAD, and to add history ; records for BZERO, BSCALE. ; Minimium IDL Version: ; V6.0 (uses V6.0 notation) ; Written : ; William Thompson, GSFC, May 1992. ; Modified : ; Version 1, William Thompson, GSFC, 12 April 1993. ; Incorporated into CDS library. ; Version 2, William Thompson, GSFC, 17 November 1993. ; Corrected bug with AVERAGE keyword on non-IEEE compatible ; machines. ; Corrected bug with subsampling on VAX machines. ; Version 3, William Thompson, GSFC, 31 May 1994 ; Added ERRMSG keyword. ; Version 4, William Thompson, GSFC, 23 June 1994 ; Modified so that ERRMSG is not touched if not defined. ; Version 5, Zarro (SAC/GSFC), 14 Feb 1997 ; Added I/O error checking ; Version 6, 20-May-1998, David Schlegel/W. Thompson ; Allow a single pixel to be read in. ; Change the signal to read in the entire array to be -1 ; Version 7 C. Markwardt 22 Sep 2003 ; If the image is empty (NAXIS EQ 0), or NODATA is set, then ; return only the header. ; Version 8 W. Landsman 29 June 2004 ; Added COMPRESS keyword, check for .gz extension ; Version 9, William Thompson, 19-Aug-2004 ; Make sure COMPRESS is treated as a scalar ; Version 10, Craig Markwardt, 01 Mar 2004 ; Add EXTENSION keyword and ability to read different ; extensions than the primary one. ; Version 11, W. Landsman September 2006 ; Assume since V5.5, remove VMS support ; Version 11.1, W. Landsman November 2007 ; Allow for possibility number of bytes requires 64 bit integer ; Version 12, William Thompson, 18-Jun-2010, update BLANK value. ; Version 13, W. Landsman Remove IEEE_TO_HOST, V6.0 notation ; Version 14, William Thompson, 25-Sep-2014, fix BSCALE bug in version 13 ; Version 15, William Thompson, 24-Jul-2017, allow NAXISn=0 if n>NAXIS ; Version 16, W. Landsman 25-Sep-2017, allow NAXISn=0 ;- ; ON_ERROR, 2 ; ; This parameter will be used later in conjunction with the average keyword. ; ALREADY_CONVERTED = 0 READ_OK=0 ; ; Parse the input parameters. ; CASE N_PARAMS() OF 2: BEGIN & I1=-1 & I2=-1 & J1=-1 & J2=-1 & STEP=1 & END 3: BEGIN & I1=-1 & I2=-1 & J1=-1 & J2=-1 & STEP=1 & END 4: BEGIN & I1=-1 & I2=-1 & J1=-1 & J2=-1 & STEP=P1 & END 5: BEGIN & I1=P1 & I2=P2 & J1=-1 & J2=-1 & STEP=1 & END 6: BEGIN & I1=P1 & I2=P2 & J1=-1 & J2=-1 & STEP=P3 & END 7: BEGIN & I1=P1 & I2=P2 & J1=P3 & J2=P4 & STEP=1 & END 8: BEGIN & I1=P1 & I2=P2 & J1=P3 & J2=P4 & STEP=P5 & END ELSE: BEGIN MESSAGE = 'Syntax: FXREAD, FILENAME, DATA ' + $ '[, HEADER [, I1, I2 [, J1, J2 ] [, STEP ]]' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE END ENDCASE ;; Extension number IF N_ELEMENTS(EXTENSION0) EQ 0 THEN EXTENSION = 0L $ ELSE EXTENSION = EXTENSION0[0] SZ = SIZE(EXTENSION) ETYPE = SZ[SZ[0]+1] IF ETYPE EQ 8 THEN BEGIN MESSAGE = 'EXTENSION must not be a structure' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF ; ; Determine if file is compressed, get the UNIT number, and open the file. ; IF NOT KEYWORD_SET(COMPRESS) THEN $ COMPRESS = STRLOWCASE( STRMID(FILENAME, STRLEN(FILENAME)-3,3)) EQ '.gz' OPENR, UNIT, FILENAME, /GET_LUN, ERROR=ERROR,COMPRESS=COMPRESS[0] IF ERROR NE 0 THEN BEGIN MESSAGE='Error opening '+FILENAME IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF ; ; Read in the FITS header. ; ;; Starting extension number is zero I_EXT = 0L FOUND_EXT = 0 WHILE NOT FOUND_EXT DO BEGIN FXHREAD,UNIT,HEADER,STATUS IF STATUS NE 0 THEN BEGIN FREE_LUN,UNIT MESSAGE = 'Unable to read requested FITS header extension' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF ; ; Extract the keywords BITPIX, NAXIS, NAXIS1, ... ; START = 0L BITPIX = FXPAR(HEADER,'BITPIX', START=START) NAXIS = FXPAR(HEADER,'NAXIS', START=START) GCOUNT = FXPAR(HEADER,'GCOUNT', START=START) IF GCOUNT EQ 0 THEN GCOUNT = 1 PCOUNT = FXPAR(HEADER,'PCOUNT', START=START) IF NAXIS GT 0 THEN BEGIN DIMS = FXPAR(HEADER,'NAXIS*') ;Read dimensions NDATA = DIMS[0] IF NAXIS GT 1 THEN FOR I=2,NAXIS DO NDATA = NDATA*DIMS[I-1] ENDIF ELSE NDATA = 0 NBYTES = LONG64(ABS(BITPIX) / 8) * GCOUNT * (PCOUNT + NDATA) NREC = (NBYTES + 2879) / 2880 IF ETYPE EQ 7 THEN BEGIN EXTNAME = STRTRIM(STRUPCASE(FXPAR(HEADER,'EXTNAME', $ START=START)),2) IF EXTNAME EQ EXTENSION THEN FOUND_EXT = 1 END ELSE IF I_EXT EQ EXTENSION THEN FOUND_EXT = 1 IF NOT FOUND_EXT THEN BEGIN ;; Check to be sure there are extensions IF I_EXT EQ 0 THEN BEGIN IF NOT FXPAR(HEADER,'EXTEND', START=START) THEN BEGIN FREE_LUN,UNIT MESSAGE = 'Requested extension not found, and file ' + $ FILENAME + ' does not contain extensions' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF ENDIF POINT_LUN, -UNIT, POINTLUN ;Current position MHEAD0 = POINTLUN + NREC*2880L POINT_LUN, UNIT, MHEAD0 ;Next FITS extension I_EXT++ ENDIF ENDWHILE ;; ;; If we got here, then we have arrived at the requested ;; extension. We still need to be sure that it is an image ;; and not a table (for extensions beyond the primary one, ;; that is). ;; IF I_EXT GT 0 THEN BEGIN XTENSION = STRTRIM(STRUPCASE(FXPAR(HEADER,'XTENSION', START=START)),2) IF (XTENSION NE 'IMAGE') THEN BEGIN FREE_LUN,UNIT MESSAGE = 'Extension ' + STRTRIM(EXTENSION,2) + $ ' is not an image' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF ENDIF IF NAXIS GT 0 THEN BEGIN DIMS = FXPAR(HEADER,'NAXIS*') DIMS = DIMS[0:NAXIS-1] NDATA = PRODUCT(DIMS, /INTEGER) ENDIF ELSE NDATA = 0 ;; Handle case of empty image, or no data requested IF NDATA EQ 0 OR KEYWORD_SET(NODATA) THEN BEGIN ;; Make DATA an undefined variable, reflecting no data DATA = 0 & DUMMY = TEMPORARY(DATA) ERRMSG = '' FREE_LUN,UNIT RETURN ENDIF N1 = DIMS[0] IF NAXIS EQ 2 THEN N2 = DIMS[1] ELSE N2 = 1 ; ; Determine the array type from the keyword BITPIX. ; CASE BITPIX OF 8: IDLTYPE = 1 ; Byte 16: IDLTYPE = 2 ; Integer*2 32: IDLTYPE = 3 ; Integer*4 -32: IDLTYPE = 4 ; Real*4 -64: IDLTYPE = 5 ; Real*8 ENDCASE ; ; Set the default values for the optional parameters. ; IF (I1 EQ -1) && (I2 EQ -1) THEN BEGIN I1 = 0 I2 = N1-1 ENDIF IF (J1 EQ -1) && (J2 EQ -1) THEN BEGIN J1 = 0 J2 = N2-1 ENDIF ; ; If the prompt keyword was set, the prompt for the parameters. ; IF KEYWORD_SET(PROMPT) THEN BEGIN ANSWER = '' READ,'Enter lower limit for X ['+STRTRIM(I1,2)+']: ', ANSWER IF ANSWER NE '' THEN I1 = (ANSWER) ; ANSWER = '' READ,'Enter upper limit for X ['+STRTRIM(I2,2)+']: ', ANSWER IF ANSWER NE '' THEN I2 = LONG(ANSWER) ; ANSWER = '' READ,'Enter lower limit for Y ['+STRTRIM(J1,2)+']: ', ANSWER IF ANSWER NE '' THEN J1 = LONG(ANSWER) ; ANSWER = '' READ,'Enter upper limit for Y ['+STRTRIM(J2,2)+']: ', ANSWER IF ANSWER NE '' THEN J2 = LONG(ANSWER) ; ANSWER = '' READ,'Enter step size ['+STRTRIM(STEP,2)+']: ', ANSWER IF ANSWER NE '' THEN STEP = LONG(ANSWER) ENDIF ; ; Differentiate between XSTEP and YSTEP. ; XSTEP = STEP > 1 IF N_ELEMENTS(Y_STEP) EQ 1 THEN YSTEP = Y_STEP ELSE YSTEP = XSTEP ; ; If any of the optional parameters were passed, then update the dimensions ; accordingly. First check I1 and I2. ; IF (I1 NE 0) || (I2 NE N1-1) THEN BEGIN IF NAXIS GT 2 THEN BEGIN FREE_LUN,UNIT MESSAGE = 'Range parameters can only be set for ' + $ 'one or two-dimensional arrays' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF IF (MIN([I1,I2]) LT 0) OR (MAX([I1,I2]) GE DIMS[0]) THEN BEGIN FREE_LUN,UNIT MESSAGE = 'I1,I2 must be in the range 0 to ' + $ STRTRIM(DIMS[0]-1,2) IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE END ELSE IF I1 GT I2 THEN BEGIN MESSAGE = 'I2 must be >= I1' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF DIMS[0] = I2 - I1 + 1 ENDIF ; ; Next, check J1 and J2. ; IF (J1 NE 0) || (J2 NE N2-1) THEN BEGIN IF NAXIS NE 2 THEN BEGIN FREE_LUN,UNIT MESSAGE = 'J1, J2 can only be set for ' + $ 'two-dimensional arrays' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF IF (MIN([J1,J2]) LT 0) OR (MAX([J1,J2]) GE DIMS[1]) THEN BEGIN FREE_LUN,UNIT MESSAGE = 'J1,J2 must be in the range 0 to ' + $ STRTRIM(DIMS[1]-1,2) IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE END ELSE IF J1 GT J2 THEN BEGIN MESSAGE = 'J2 must be >= J1' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF DIMS[1] = J2 - J1 + 1 ENDIF ; ; Next, check XSTEP. Note that the dimensions of the final result are ; somewhat differ depending on whether the keyword AVERAGE is set or not. ; IF XSTEP GT 1 THEN BEGIN IF NAXIS GT 2 THEN BEGIN FREE_LUN,UNIT MESSAGE = 'STEP can only be set for one or ' + $ 'two-dimensional arrays' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE END ELSE IF XSTEP NE LONG(XSTEP) THEN BEGIN FREE_LUN,UNIT MESSAGE = 'STEP must be an integer value' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE END ELSE IF KEYWORD_SET(AVERAGE) THEN BEGIN DIMS[0] = DIMS[0] / LONG(XSTEP) END ELSE BEGIN DIMS[0] = LONG(DIMS[0] + XSTEP - 1) / LONG(XSTEP) INDEX = LINDGEN(DIMS[0])*XSTEP ENDELSE ENDIF ; ; Finally, check YSTEP. This parameter is ignored for anything other than ; two-dimensional arrays. ; IF (NAXIS EQ 2) && (YSTEP GT 1) THEN BEGIN IF YSTEP NE LONG(YSTEP) THEN BEGIN FREE_LUN,UNIT MESSAGE = 'YSTEP must be an integer value' IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE END ELSE IF KEYWORD_SET(AVERAGE) THEN BEGIN DIMS[1] = DIMS[1] / LONG(YSTEP) END ELSE BEGIN DIMS[1] = LONG(DIMS[1]+YSTEP-1) / LONG(YSTEP) ENDELSE END ELSE YSTEP = 1 ; ; Make the array. ; DATA = MAKE_ARRAY(DIMENSION=DIMS,TYPE=IDLTYPE,/NOZERO) ; ; Find the start of the data to be read in. ; POINT_LUN,-UNIT,OFFSET ;Current position DELTA = N1*ABS(BITPIX)/8 IF J1 NE 0 THEN BEGIN OFFSET = OFFSET + LONG64(J1)*DELTA POINT_LUN,UNIT,OFFSET ENDIF ; ; If the I range, XSTEP or YSTEP is non-trivial, then read in the file line by ; line. If pixel averaging, then read in YSTEP lines. ; ON_IOERROR,QUIT IF (DIMS[0] NE N1) || (XSTEP GT 1) || (YSTEP GT 1) THEN BEGIN IF NAXIS EQ 1 THEN NJ = 1 ELSE NJ = DIMS[1] FOR J = 0,NJ-1 DO BEGIN IF YSTEP GT 1 THEN POINT_LUN,UNIT,OFFSET+J*YSTEP*DELTA IF (YSTEP GT 1) && KEYWORD_SET(AVERAGE) && (NAXIS EQ 2) $ THEN LINE = MAKE_ARRAY(N1,YSTEP,TYPE=IDLTYPE,/NOZERO) $ ELSE LINE = MAKE_ARRAY(N1,TYPE=IDLTYPE,/NOZERO) READU,UNIT,LINE ; ; If I1,I2 do not match the array size, then extract the relevant subarray. ; IF (I1 NE 0) || (I2 NE N1-1) THEN LINE = LINE[I1:I2,*] ; ; Suppose that the step size is non-trivial. If AVERAGE was set, then convert ; to the host format, and use REBIN to average the data. (Note that missing ; pixels are not correctly handled in this case.) Otherwise, select out the ; relevant portion of the data. ; IF (XSTEP GT 1) || (YSTEP GT 1) THEN BEGIN IF KEYWORD_SET(AVERAGE) THEN BEGIN SWAP_ENDIAN_INPLACE, LINE, /SWAP_IF_LITTLE ALREADY_CONVERTED = 1 IF NAXIS EQ 1 THEN BEGIN DATA[0,J] = REBIN(LINE[0:XSTEP*DIMS[0]]-1,DIMS[0]) END ELSE BEGIN DATA[0,J] = REBIN(LINE[0:XSTEP*DIMS[0]-1,*],DIMS[0],1) ENDELSE END ELSE DATA[0,J] = LINE[INDEX] ; ; Otherwise, if the step size is trivial, then simply store the line in the ; data array. ; END ELSE BEGIN DATA[0,J] = LINE ENDELSE ENDFOR ; ; Otherwise, if the file doesn't have to be read in line by line, then just ; read the data array. ; END ELSE READU,UNIT,DATA ; ; Convert the data from IEEE to host format, keeping track of any IEEE NaN ; values. Don't do this if the conversion has already taken place. ; IF ~ALREADY_CONVERTED THEN BEGIN IF (N_ELEMENTS(NANVALUE) EQ 1) && (IDLTYPE GE 4) && $ (IDLTYPE LE 6) THEN W = WHERENAN(DATA,COUNT) ELSE $ COUNT = 0 SWAP_ENDIAN_INPLACE,DATA, /SWAP_IF_LITTLE END ELSE COUNT = 0 ; ; If the parameters BZERO and BSCALE are non-trivial, then adjust the array by ; these values. Also update the BLANK keyword, if present. ; IF ~KEYWORD_SET(NOSCALE) THEN BEGIN BZERO = FXPAR(HEADER,'BZERO') BSCALE = FXPAR(HEADER,'BSCALE') BLANK = FXPAR(HEADER,'BLANK',COUNT=NBLANK) GET_DATE,DTE IF (BSCALE NE 0) && (BSCALE NE 1) THEN BEGIN DATA *= BSCALE IF ~KEYWORD_SET(NOUPDATE) THEN BEGIN FXADDPAR,HEADER,'BSCALE',1. FXADDPAR,HEADER,'HISTORY',DTE + $ ' applied BSCALE = '+ STRTRIM(BSCALE,2) IF NBLANK EQ 1 THEN BEGIN print, bscale, blank BLANK *= BSCALE FXADDPAR,HEADER,'BLANK',BLANK ENDIF ENDIF ENDIF IF BZERO NE 0 THEN BEGIN DATA += BZERO IF ~KEYWORD_SET(NOUPDATE) THEN BEGIN FXADDPAR,HEADER,'BZERO',0. FXADDPAR,HEADER,'HISTORY',DTE + $ ' applied BZERO = '+ STRTRIM(BZERO,2) IF NBLANK EQ 1 THEN BEGIN BLANK += BZERO FXADDPAR,HEADER,'BLANK',BLANK ENDIF ENDIF ENDIF ENDIF ; ; Store NANVALUE everywhere where the data corresponded to IEE NaN. ; IF COUNT GT 0 THEN DATA[W] = NANVALUE ; ; Close the file and return. ; READ_OK=1 QUIT: ON_IOERROR,NULL FREE_LUN, UNIT IF NOT READ_OK THEN BEGIN MESSAGE='Error reading file '+FILENAME IF N_ELEMENTS(ERRMSG) NE 0 THEN BEGIN ERRMSG = MESSAGE RETURN END ELSE MESSAGE, MESSAGE ENDIF IF N_ELEMENTS(ERRMSG) NE 0 THEN ERRMSG = '' RETURN END