[gradsusr] big/little endian bug in OpenGrads v2.0.a9.oga.1 for 2-byte integers files

[Jennifer Adams]

I have fixed the bug regarding the endian-ness of 2-byte signed/ 
unsigned integers. As for the secondary issue that David Lorenz  
brought up, I have updated the documentation, which now states: "If  
there are multiple variables in the same file, they must all be the  
same type." This is for binary data only, and it is because the  
calculation of file offsets (i.e. where to move to in the file to read  
the requested data) requires that all x-y grids in the file are the  
same size in bytes. Variables of different sizes are easily handled in  
the netcdf interface -- if you require a mix of shorts, ints, and byte  
variables in one file, please use netcdf format instead of binary.
--Jennifer




On May 20, 2011, at 11:22 AM, Jennifer Adams wrote:

> I will take a look at this bug as soon as I can. Thanks for all the  
> helpful diagnostic material. Although it doesn't say it explicitly  
> in the documentation, I don't think the 'special format' codes in  
> the units field of the variable declaration for non-standard binary  
> data were ever intended to be used on a per-variable basis. When  
> looking at this bug, I will make sure that is the case and update  
> the documentation as appropriate. If you want to write out variables  
> of different binary formats in the same file, I think netCDF is  
> probably the better format for that. GrADS will handle a variety of  
> data types in the same file automatically without any fuss or muss.  
> --Jennifer
>
> On May 20, 2011, at 11:06 AM, David Lorenz wrote:
>
>> I've run into the same problem in the GrADS binary for Mac. I sent  
>> a message to these forums a while back and didn't get a response.
>>
>> There's also a problem when you mix two-byte and four-byte  
>> variables together in the same file. GrADS get confused and acts  
>> like all variables are the same size as the variable you are trying  
>> to display.
>>
>>
>> -Dave
>>
>> On 05/19/11, Henrique Barbosa   wrote:
>>> Dear all,
>>>
>>> I was trying to read a single variable written as 2-byte signed  
>>> integer in a big endian file. Plain binary file, i.e. stream, with  
>>> no header. Should be really simple, but it was not. For handling  
>>> this, I had my CTL as:
>>>
>>>
>>>
>>> (...)
>>> options big_endian
>>> (...)
>>> myvar 0 -1,40,2,-1 ** my variable
>>> (...)
>>>
>>> However, it did not work. The values were completely wrong. After  
>>> a day trying to understand what as going on, I decided to force  
>>> 'little_endian' on the CTL despite the file being big- 
>>> endian... and it worked!! and I could read the data.
>>>
>>>
>>>
>>> However, USGS claims gtopo30 to be big_endian. To make sure,  I  
>>> wrote a  F90 program to read it. I could only get the correct data  
>>> inside the program if I opened the file as big_endian. Therefore,  
>>> as USGS and my program agree, I believe the data is big_endian.
>>>
>>>
>>>
>>> Therefore the problem should be in grads. I made a series of  
>>> tests, writing 1-byte, 2-byte and 4-byte integer binary files, and  
>>> 4-byte float files, for both little and big endian types. The only  
>>> problem I found was with 2-byte integers. I think that it is a bug  
>>> in grads, actually, OpenGrads v2.0.a9.oga.1. The necessary data to  
>>> reproduce the problem can be found here:
>>>
>>>
>>>
>>>
>>>
>>> <http://www.fap.if.usp.br/~hbarbosa/file_format.tgz>
>>>
>>>
>>>
>>> Can some expert have a look in the source code? Arlindo? Jennifer?  
>>> By the way, I am on x86-64 machine, runing ubuntu 64bits and using  
>>> grads-2.0.a9.oga.1-bundle-x86_64-rhel5.5-linux-gnu.tar.gz.
>>>
>>> Sincerely,
>>> Henrique
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> gradsusr mailing list
>>> gradsusr at gradsusr.org
>>> http://gradsusr.org/mailman/listinfo/gradsusr
>>
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>
> --
> Jennifer M. Adams
> IGES/COLA
> 4041 Powder Mill Road, Suite 302
> Calverton, MD 20705
> jma at cola.iges.org
>
>
>
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--
Jennifer M. Adams
IGES/COLA
4041 Powder Mill Road, Suite 302
Calverton, MD 20705
jma at cola.iges.org



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