Re: binary read

The issue was that the binary file was generated on an older Mac, which was a PowerPC. The newer Mac which the file was being read on is an Intel Mac.

PowerPC is big endian and Intel is little endian, so this is an issue when reading binary files. There's no way for any software to tell automatically if a file was written on a big or little endian machine. You have to "help" it by calling setfileoption to set the ReadByteOrder parameter as described below.

Note that you can force a file to be written one way or another by also using setfileoption to set the "WriteByteOrder" to "BigEndian" or "LittleEndian".

--Mary

On Jul 29, 2010, at 9:51 AM, Mary Haley wrote:

> Hi Michael,
>
> We didn't make any changes to the binary read functions that I can think of. I don't really have enough information to know what the problem could be.
>
> You might be running into one of two issues:
>
> 1. Big endian versus little endian - did you write this file on a little endian (or vice versa) system, and now are trying to it on a big endian (or vice versa) system? If so, you might need to call "setfileoption" before you read the file to set the appropriate endianness:
>
> setfileoption("bin","ReadByteOrder","LittleEndian")
> or
>
> setfileoption("bin","ReadByteOrder","BigEndian")
>
> 2. The other possible issue that this might might have been written such that an 8-byte record was written at the beginning of the file.
>
> This can happen if the file was written with a Fortran program that was compiled with an older version of g77 or gfortran that wrote 8-byte headers by default. This has changed with newer versions of gfortran.
>
> --Mary
>
> On Jul 28, 2010, at 3:34 PM, Michael Notaro wrote:
>
>> On a previous version of NCL, I used this script and was able to read
>> binary data fine. Now I am using NCL 5.2 and have recently rerun the
>> script to find that all the values that are read in are now garbage.
>> What do I need to change to read the binary files correctly?
>>
>> Thanks, Michael
>>
>>
>>
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
>> load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/shea_util.ncl"
>>
>> begin
>>
>> names=asciiread("filenames",(/600/),"string")
>>
>> a = fbindirread("/Users/notaro/ndvi/namer_albers.lat",0,(/1024,1280/),"short")
>> lat2d=short2flt(a)
>> lat2d=lat2d/100.
>> b = fbindirread("/Users/notaro/ndvi/namer_albers.lon",0,(/1024,1280/),"short")
>> lon2d=short2flt(b)
>> lon2d=lon2d/100.
>> lat2d!0="lat"
>> lat2d!1="lon"
>> lon2d!0="lat"
>> lon2d!1="lon"
>> lat2d@units="degrees_north"
>> lon2d@units="degrees_east"
>>
>> sw=new((/600/),float)
>>
>> do i=0,599
>>
>> d = fbindirread("/Users/notaro/ndvi/namer_all/"+names(i),0,(/1024,1280/),"short")
>> var=(/short2flt(d)/)
>> var=var/10000.
>>
>> var!0="lat"
>> var!1="lon"
>> var@lat2d=lat2d
>> var@lon2d=lon2d
>>
>> sw(i)=(/avg(var(692:694,597:599))/)
>>
>> end do
>>
>> ETC............
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Received on Thu Jul 29 15:49:25 2010