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[netCDF #RJZ-836571]: problem converting netcdf4 files to netCDF4-classic

Hello Cathy,

Thank you for providing the file; it certainly helped me debug this issue!

The problem appears to be that the uses a group, `Grid`.  There isn't an easy 
way to remove the group with `ncdump` or `nccopy`, although NCO may let you do 
this.  Alternatively, I was able to fix this with an intermediary step. 

I dumped the file you provided to a `.cdl` file as follows:

    $ ncdump precip.imerge.mon.202312.nc > tmp.cdl

I then edited the cdl file to remove the `group: Grid {` line near the start of 
the file, and removed the corresponding closing '}' at the end of the file. I 
was then able to generate a binary `.nc` file using `ncgen` as follows:

    $ ncgen -7 -o tmp.nc tmp.cdl

Running `ncdump -k tmp.nc` returns `netCDF-4 classic model`.

That at least should answer the question; I will look into if there is an 
easier way to do this, but at the moment I'm not certain there is.

I hope this helps!

-Ward

> Hi all
> 
> We have run into issues converting files from netCDF4 to netCDF4-classic.
> 
> The problem is this
> 
>   nccopy -k 4 precip.imerg.mon.202312.nc a.nc
> NetCDF: Attempting netcdf-4 operation on strict nc3 netcdf-4 file
> Location: file ../../ncdump/nccopy.c; line 657
> 
> and similarly for
> 
>   nccopy -k "netCDF-4 classic model"  a.nc
> 
> ncdump gives
> 
>    ncdump -k precip.imerg.mon.202312.nc
> netCDF-4
> 
> and
> 
>   ncdump -hs precip.imerg.mon.202312.nc
> 
> skip stuff
> 
>       float precip(time, lon, lat) ;
>           precip:DimensionNames = "time,lon,lat" ;
>           precip:Units = "mm/hr" ;
>           precip:units = "mm/hr" ;
>           precip:coordinates = "time lon lat" ;
>           precip:_FillValue = -9999.9f ;
>           precip:CodeMissingValue = "-9999.9" ;
>           precip:LongName = "Merged microwave-infrared-gauge
> precipitation estimate" ;
>           precip:_Storage = "chunked" ;
>           precip:_ChunkSizes = 1, 145, 1800 ;
>           precip:_DeflateLevel = 6 ;
>           precip:_Endianness = "little" ;
> 
> skip stuff
> 
>  // group attributes:
>           :GridHeader =
> "BinMethod=ARITHMETIC_MEAN;\nRegistration=CENTER;\nLatitudeResolution=0.1;\nLongitudeResolution=0.1;\nNorthBoundingCoordinate=90;\nSouthBoundingCoordinate=-90;\nEastBoundingCoordinate=180;\nWestBoundingCoordinate=-180;\nOrigin=SOUTHWEST;\n"
> ;
>   } // group Grid
> 
> GrADS won't plot the files
> 
> Scanning self-describing file:  precip.imerg.mon.202312.nc
> gadsdf: SDF file has no discernable X coordinate.
>   To open this file with GrADS, use a descriptor file with an XDEF entry.
>   Documentation is at
> http://cola.gmu.edu/grads/gadoc/SDFdescriptorfile.html
> 
> But of course the variable does have a good X coordinate
> 
> CDO gives a similar error to the NCO command for converting
> 
> cdo -f nc4c -O copy precip.imerg.mon.202312.nc
> <http://precip.imerg.mon.202312.nc> ~/a.nc <http://a.nc>
> Segmentation fault
> 
> Is there anyway to convert the files from the command line from netCDF4
> to netCDF4-classic? We had the same issue with some unrelated files
> produced from python code.
> 
> I've put one file into /Public/csmith/
> 
> precip.imerg.mon.202312.nc
> 
> ftp ftp.cdc.noaa.gov
> 
> Thanks for any advice!
> 
> Cathy Smith
> 
> --
> ----------------------------------------------------------------
> Cooperative Institute for Research in Environmental Sciences ,
> University of Colorado Boulder
> Working in the NOAA Physical Sciences Laboratory
> https://psl.noaa.gov/people/cathy.smith/
> https://cires.colorado.edu/people/cathy-smith
> 
> Emails about data/webpages may get quicker responses by emailing
> address@hidden
> 
> 


Ticket Details
===================
Ticket ID: RJZ-836571
Department: Support netCDF
Priority: Normal
Status: Closed
===================
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