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