pro mrd_hread, unit, header, status, SILENT = silent, FIRSTBLOCK = firstblock ;+ ; NAME: ; MRD_HREAD ; ; PURPOSE: ; Reads a FITS header from an opened disk file or Unix pipe ; EXPLANATION: ; Like FXHREAD but also works with compressed Unix files ; ; CALLING SEQUENCE: ; MRD_HREAD, UNIT, HEADER [, STATUS, /SILENT ] ; INPUTS: ; UNIT = Logical unit number of an open FITS file ; OUTPUTS: ; HEADER = String array containing the FITS header. ; OPT. OUTPUTS: ; STATUS = Condition code giving the status of the read. Normally, this ; is zero, but is set to -1 if an error occurs, or if the ; first byte of the header is zero (ASCII null). ; OPTIONAL KEYWORD INPUT: ; /SILENT - If set, then warning messages about any invalid characters in ; the header are suppressed. ; /FIRSTBLOCK - If set, then only the first block (36 lines or less) of ; the FITS header are read into the output variable. If only ; size information (e.g. BITPIX, NAXIS) is needed from the ; header, then the use of this keyword can save time. The ; file pointer is still positioned at the end of the header, ; even if the /FIRSTBLOCK keyword is supplied. ; RESTRICTIONS: ; The file must already be positioned at the start of the header. It ; must be a proper FITS file. ; SIDE EFFECTS: ; The file ends by being positioned at the end of the FITS header, unless ; an error occurs. ; REVISION HISTORY: ; Written, Thomas McGlynn August 1995 ; Modified, Thomas McGlynn January 1996 ; Changed MRD_HREAD to handle Headers which have null characters ; A warning message is printed out but the program continues. ; Previously MRD_HREAD would fail if the null characters were ; not in the last 2880 byte block of the header. Note that ; such characters are illegal in the header but frequently ; are produced by poor FITS writers. ; Converted to IDL V5.0 W. Landsman September 1997 ; Added /SILENT keyword W. Landsman December 2000 ; Added /FIRSTBLOCK keyword W. Landsman February 2003 ;- block = string(replicate(32b, 80, 36)) w = [-1] nblock = 0 while w eq -1 do begin ; Shouldn't get eof in middle of header. if eof(unit) then begin free_lun, unit status = -1 return endif on_ioerror, error_return readu, unit, block on_ioerror, null ; Check that there aren't improper null characters ; in strings that are causing them to be truncated. ; Issue a warning but continue if problems are found. w = where(strlen(block) ne 80) if (w ne -1) then begin if not keyword_set(SILENT) then message, /INF, $ 'Warning-Invalid characters in header' block[w] = string(replicate(32b, 80)) endif w = where(strmid(block, 0, 8) eq 'END ') if nblock EQ 0 then begin if w eq -1 then header = block $ else header = [block[0:w]] nblock = nblock + 1 endif else begin if not keyword_set(firstblock) then begin if w eq -1 then header = [header, block] $ else header = [header, block[0:w]] endif endelse endwhile status = 0 return error_return: status = -1 return end
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|Last modified on 2nd Mar 2009 by Richard Massey.|