[SciPy-user] Problem with reading binary file (diffrener resultbetween MATLAB and Python)

[Hani Zahiri]

Hi Robert,

Many Thanks, you were right and it's work. Since, I run both MATLAB and
Python on windows, I didn't suspect byte order issue.
Probably, original file was generated using different byte order. Is it
the case that MATLAB can recognise the original byte order (because it
is platform-independent) and Python does not?!

Anyway, many thanks. You made my day!

Cheers,

Hani  


-----Original Message-----
From: scipy-user-bounces at scipy.org [mailto:scipy-user-bounces at scipy.org]
On Behalf Of Robert Kern
Sent: Sunday, 11 January 2009 10:13 PM
To: SciPy Users List
Subject: Re: [SciPy-user] Problem with reading binary file (diffrener
resultbetween MATLAB and Python)

On Sun, Jan 11, 2009 at 06:48, Hani Zahiri <H.Zahiri at curtin.edu.au>
wrote:
> Hi folks,
>
>
>
> I am trying to translate one of my MATLAB scripts to Python and I am
> experiencing a strange problem (at least to me!) and I am desperetly
looking
> for help. The binary file is a raw binary containing header
information
> (first 720 bytes) following by radar data. For better illustration and
using
> python basic functions, first 800 bytes of the file is look like this:
>
>
>
>>>> fid = open("file_name","rb")
>
>>>> fid.read(800)
>
> '\x00\x00\x00\x012\xc0\x12\x12\x00\x00\x02\xd0A   CEOS-SAR-CCT A A
> 1.00          1AL1 PSRBIMOP    FSEQ       1   4FTYP       5   4FLGT
> 9   4
> 18432 88220                          32   2   8       1   18432   0
> 10976   0   0   0BSQ  1 1 412   87808   0      13 4PB  49 2PB  45 4PB
21
> 4PB  29 4PB                                  97 4PB
> COMPLEX*8                   C*8    0
> 0
>
\x00\x00\x00\x022\n\x12\x14\x00\x01X\x9c\x00\x00\x00\x01\x00\x00\x00\x01
\x00\x00\x00\x00\x00\x00*\xe0\x00\x00\x00\x00\x00\x00\x00\x00\
> ...
>
x00\x00\x07\xd6\x00\x00\x00\x8d\x02\xdd\xfe\x95\x00\x01\x00\x00\x00\x00\
x00\x00\x00\x1c\xae\x93\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00ix
> ...
>
> \x00\x00\x00\x00I}.\xd0'
>
>
>
> And now the problem is:
>
> If I read the file in MATLAB, let say to find out length of header
part, I
> will get the correct answer:
>
>
>
> EDU>> fid=fopen('file_name','r','b');
>
> EDU>> fseek(fid,8,'bof');
>
> EDU>> fread(fid,1,'uint32')
>
>
>
> ans =
>
>
>
>    720
>
>
>
> However if I read this in python I am keep getting this wrong:
>
>>>> fid.seek(8)
>
>>>> scipy.fromfile(fid,'uint32',1)
>
> array([3489792000], dtype=uint32)

I suspect that you are running your Matlab script on a bigendian
machine and your Python script on a littleendian machine. The length
marker in your file is bigendian. Use dtype='>i4' to read it. You will
probably also need to use bigendian dtypes for the rest of the data,
too.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco
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