From: Wolfgang <wollez@...>
Date: 2006-03-30T01:13:43+09:00
Subject: Re: reading/writing binary problem

Hello,

yes I want to extract a matrix of 1024x1024 of binary data (2bytes for 
each value). But ahead of this data is 1048576 bit (13312 bytes) of 
crap. I don't know matlab at all and I don't like to start this routine 
when I want to import that data into my application, which can not skip 
this header. If it is easier to do by a linux command (its running in 
cygwin) any help is also welcome.

Wolfgang

PS: I will also test the example of Robert


ara.t.howard@noaa.gov schrieb:
> On Wed, 29 Mar 2006, Wolfgang wrote:
> 
>> Hi,
>>
>> I have some binary files which I need to delete some data at the 
>> beginning of the file (to extract the raw data out of the file). I got 
>> a matlab file from a colleque but I would prefer if I could do it with 
>> ruby.
>>
>> This matlab code does the trick:
>>     function m=write_rad(filename)
>>     file=fopen(filename);
>>     f= fread(file,'uint16');
>>
>>     [r,k]=size(f);
>>     if k==1;
>>           t=r-1048576;
>>           m=f(t+1:r,:);
>>     end
>>     end % function
>>
>> How can I do this in ruby? I'm completely lost.
>>
>> Thanks
>> Wolfgang
> 
> this sould be easy if i understood that method and the nature of your 
> data ;-)
> 
> here's what i understand this method to do :
> 
>   # open the file
> 
>     file=fopen(filename);
> 
>   # read all available unit16 quantities into an [m, n] array
> 
>     f= fread(file,'uint16');
> 
>   # check the size of this array, r is the number of elements read
> 
>     [r,k]=size(f);
> 
>   # k will be one iff data was read into r dimension
> 
>     if k==1;
> 
>   # here i assume 1048576 is the 'row_size' of 1mb.  we set t to be the 
> offset
>   # of the last row
> 
>     t=r-1048576;
> 
>   # because matlab is evil and uses one based indexing, we inc t by one and
>   # extract the last row/block of data.  but here it seems like the ith 
> index
>   # should be t+1:r-1048576 no?  otherwise it seems like this would be 
> out of
>   # bounds?
> 
>     m=f(t+1:r,:);
> 
> 
> in any case this looks alot like you are trying to extract the last 1mb of
> uint16 quantities from a data file - is that right?  let me know and 
> i'll show
> you how to do this.
> 
> regards.
> 
> -a