| Re: How does one read in simple binary files? [message #5530] |
Mon, 15 January 1996 00:00 |
hahn
Messages: 108
Registered: November 1993
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Senior Member |
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Several good examples were given but ....
thompson@achilles.nascom.nasa.gov (William Thompson) wrote:
> Yep.
> All you would need to do for your example of a 128x128 array would be the
> following:
> IDL> OPENR, UNIT, 'filename1', /GET_LUN
As the poster of the original question didn't not mention which
programing language was used to write the binary data I want to
point to an additional keyword for IDL's open procedures. It is
/fortran_77 which takes care of extra words the run time system
of Fortran adds for binary files. Binary Fortran files have the
record length of transferred record prepended and appended
to the record, *if the operating system is some Unix flavor*.
In following Fortran chunk will read 10 elements of a real array
from standard input and write it as one binary record on unit 27:
real x(10)
read(*,*) x
write(27) x
end
will result in 48 bytes being written: 4 bytes contain the record
length (40) as integer value, 40 data bytes follow, and then the
header is repeated.
> William Thompson
Norbert Hahn
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| 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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| Re: How does one read in simple binary files? [message #5543 is a reply to message #5542] |
Sat, 13 January 1996 00:00 |
kennealy
Messages: 11
Registered: August 1994
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Junior Member |
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Bruce, with IDL, reading binary files is quite simple. For example,
your case of a 128x128 image of 2-byte pixels could be handled as:
image=intarr(128,128)
openr,1,filename
readu,1,image
close,1
and that takes care of it. Your second case could be handled as
header=bytarr(100)
image=fltarr(128,128)
openr,1,filename
readu,1,header,image
close,1
Hope this helps. In this newsgroup, you'll find people are very
helpful on all levels of questions.
Regards,
Jack
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