| Re: How does one read in simple binary files? [message #5542 is a reply to message #5530] |
Sat, 13 January 1996 00:00   |
thompson
Messages: 584
Registered: August 1991
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Senior Member |
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bmac@igpp.llnl.gov (Bruce Macintosh) writes:
> This is an incredibly basic question: what's the simplest way
> to read in a simple binary file (ie an file of 16384 2-byte integers
> representing a 128x128 pixel image, for example), or slightly
> more complicated binary files (an array of 16384 IEEE 32-bit reals
> with a 100-byte header preceeding the pixel values, for example.)
> Are there any standard packages/routines for handling this kind of i/o,
> with or without byte and word swapping? All
> I can find in the manuals are routines for reading in ascii text, or
> various specialized formats, but nothing generic. Does "unformatted i/o"
> (readu, etc.) do this sort of input?
Yep.
All you would need to do for your example of a 128x128 array would be the
following:
IDL> OPENR, UNIT, 'filename1', /GET_LUN
IDL> I_ARRAY = INTARR(128,128)
IDL> READU, UNIT, I_ARRAY
IDL> FREE_LUN, UNIT
or for your more complicated example
IDL> OPENR, UNIT, 'filename2', /GET_LUN
IDL> HEADER = BYTARR(100)
IDL> READU, UNIT, HEADER
IDL> F_ARRAY = FLTARR(16384) ;Or did you mean (128,128) again?
IDL> READU, UNIT, F_ARRAY
IDL> FREE_LUN, UNIT
You can also use ASSOC to do the same thing--check the documentation on the use
of ASSOC.
If the data is written in a binary format different from that of the host
computer, then it's a little more complicated. The BYTEORDER routine can be
used to convert between standard and host-specific byte ordering, and even
between IEEE and host floating point representations. The above two examples
might also include the following lines after the read statements.
IDL> BYTEORDER, I_ARRAY, /NTOHS
IDL> BYTEORDER, F_ARRAY, /XDRTOF
Personally, I recommend using the routines IEEE_TO_HOST and HOST_TO_IEEE from
the Astronomy User's Library. That way, you don't have to figure out what the
proper keyword to use with BYTEORDER.
William Thompson
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