That was badly worded. I should have said, "This is a big-endian integer
with the current dimension size, i.e. number of RECORDS, ON the unlimited
dimension."
--Dave
On Thu, Jan 19, 2017 at 4:39 PM, Dave Allured - NOAA Affiliate <
dave.allured@xxxxxxxx> wrote:
> Kevin,
>
> The information from appendix B is correct but incomplete. In netcdf-3
> classic format, bytes 4-7 are "numrecs". This is a big-endian integer with
> the current dimension size, i.e. number of elements, of the unlimited
> dimension. For netcdf-3 files with no unlimited dimension, in other words
> all fixed dimensions, numrecs is present, but the value is undefined. For
> streaming files, numrecs is defined as all four bytes = FF hex.
>
> The unlimited dimension means the same thing as the record dimension.
>
> I recommend that you use only bytes 0-3 to identify netcdf-3 files.
>
> You might also take a look at how format identification is done in a
> recent version of the "file" utility in Linux distributions. My recent
> version of "file" identifies netcdf-3 files as "NetCDF Data", and netcdf-4
> files as HDF5. My guess is that they look at only bytes 0-3 for netcdf-3,
> but I am not sure.
>
> --Dave
>
>
> On Thu, Jan 19, 2017 at 2:20 PM, HAVENER, KEVIN F GS-12 USAF ACC 14
> WS/WXED <kevin.havener@xxxxxxxxx> wrote:
>
>> I have what I am sure is a very basic question but I couldn't figure out
>> how to search the archives for it, and the documentation left me befuddled.
>>
>> I am trying to pass a netCDF3v1 file through a virus detector-like
>> software (more like a firewall-like thing) that checks for a few things to
>> ascertain the file is really a netCDF3 file. The file is global lon x lat
>> x time (1 time step) with 4 variables.
>>
>> So I've done an octal dump on the file and I'm curious about the value
>> that is supposed to be in bytes 4-7, where bytes 0-3 are "C-D-F-1".
>> Appendix B in the user's guide says these bytes are the numrecs=length of
>> the record dimension. What is that? The unlimited dimension? My example
>> file has "1" at byte 7, the example in the user's guide has 0. My
>> intuition tells me that for my file, time is considered the record
>> dimension, but it would also be OK to have 0 record dimensions in this file
>> if I don't intend to append to it.
>>
>> Is my understanding correct?
>>
>> Kevin Havener, DAFC, 14WS/WXED
>>
>>
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