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[netCDF #XEI-820003]: conversion from netCDF4 to netCDF3

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  • Subject: [netCDF #XEI-820003]: conversion from netCDF4 to netCDF3
  • Date: Fri, 21 Nov 2014 10:17:25 -0700
Hello Dan,

The data type is a function of the process creating the original netCDF4 files. 
 If the variables are float in the netCDF4 files being provided, they will 
retain the same data type when converted to netCDF3. There is not an easy way 
to convert them from float to short, unfortunately.  This  would require 
writing a program to create a new variable of type short, reading the values 
from the variable of interest, converting them to short, and assigning them to 
the new variable.

You could potentially side-step this by casting values to short in your 
application, but I can't recommend this because I don't know if this would 
cause other problems on your end.   Regarding your final question, I don't 
think there is a problem with reading the converted files; the problem stems 
from what was once a 'short' variable is now a 'float' variable.  The fact that 
it is also now a netCDF4 file is unrelated. 

I know this probably isn't as much help as you'd like, but I think the solution 
to this will be either to modify your application to handle the new data type 
of the variable, or  to write a pre-processor which will convert the files 
being provided to you into the format you expect.

Let me know if I can answer any further questions, have a great day,

-Ward

> We have an application that previously used netCDF3 files from NCAR. Since 
> they changed to netCDF4, our application fails. We started looking into 
> fixing the code. NCAR says the you can convert back to netCDF3 with the 
> nccopy command. I tried:  nccopy -k classic filenetcdf4.nc filenetcdf3.nc.  
> It looks like I get the same errors in my code using these converted files 
> instead. If I dump the files with ncdump, variable that were short in netCDF3 
> (original format fromNCAR)  are indicated to be float in both netCDF4 and in 
> the converted netCDF3. - In any case, I want to know if there is a way to 
> convert the netCDF4 files EXACTLY back to  netCDF3 files.    It seems 
> unlikely, but is it possible that now that we have recompiled our application 
> with the latest version of netCDF there is a problem reading the converted 
> files?
> 
> Dan MacMillan
> 
> 


Ticket Details
===================
Ticket ID: XEI-820003
Department: Support netCDF
Priority: Normal
Status: Closed