[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[netCDF #YLU-405033]: dealing with missing values while writing netCDF in FORTRAN V 3.6.1

Hi,

> I have problems with writing missing values in a NetCDF file. When I am
> writing netCDF files in R using âncdfâ library, I am using the following
> codes. I can declare missing value in var.def.ncdf call. Then read the file
> in R, it is read as NA. I want to do the same with FORTRAN calls windows
> built V3.6.1. I didnât find similar calls in Fortran interface
> documentation.  I know it is possible to declare â_FillValueâ to fill not
> written or missing values.  Is it possible to declare the program that a
> particular value (say -9999.00) will be used for missing value and read it
> as NA in FORTRAN?

The handling of missing values in netCDF are documented in the Users
Guide, where information that applies to all the specific language
interfaces, such as C, Fortran, C++, and Java, is found:

  http://www.unidata.ucar.edu/software/netcdf/docs/attribute_conventions.html

As you'll see there, the _FillValue variable attribute has a default
value for each primitive type, but you can also set it to any chosen
value for a variable.  It will be dislayed as "_" rather than "NA" in
ncdump output.

There is no global attribute that specifies a missing value for all
variables in a netCDF file, as variables may have different types, and
generally no single value would be suitable.

--Russ

> * R codes to write a netCDF:*
> 
> 
> *library(ncdf)*
> 
> *missval=-9999 # missing value, missval = -9999*
> 
> *xy = matrix(c(-111.8336,-111.8336,missval,-111.8336,-111.8336,missval))*
> 
> *xdim=3*
> 
> *ydim=2*
> 
> * *
> 
> *#  Names that needs changes for each variable*
> 
> *varnameD="cc"*
> 
> *unitnameID="unitless"*
> 
> *filename="longitude.nc"*
> 
> *#  Names that needs changes for each dimension*
> 
> *xcoordName="xcoord"*
> 
> *ycoordName="ycoord"*
> 
> * *
> 
> *# netCDF starts here*
> 
> *xllcorner=0*
> 
> *yllcorner=5*
> 
> *x = xllcorner + 10*(1:xdim)*
> 
> *y = yllcorner + 10*(1:ydim)*
> 
> * *
> 
> *# define the netcdf coordinate variables -- note these have values!*
> 
> *# dim.def.ncdf(name, units, vals, unlim=FALSE, create_dimvar=TRUE)*
> 
> * *
> 
> *dim2 = dim.def.ncdf( xcoordName,"meter", as.double(x))*
> 
> *dim1 = dim.def.ncdf( ycoordName,"meter", as.double(y))*
> 
> * *
> 
> *# define the EMPTY netcdf variable*
> 
> *# var.def.ncdf(name, units, dim, missval, longname=varnameD, prec="single")
> *
> 
> *varz = var.def.ncdf(varnameD,unitnameID,
> list(dim1,dim2),missval,longname=varnameD)*
> 
> * *
> 
> *# associate the netcdf variable with a netcdf file*
> 
> *# put the variable into the file, and close*
> 
> *# create.ncdf( filename, vars, verbose=FALSE )*
> 
> *nc.ex = create.ncdf(filename,list(varz))*
> 
> * *
> 
> *put.var.ncdf(nc.ex, varz, xy)*
> 
> *close.ncdf(nc.ex)*
> 
> 
> 
> *Read it with R: *
> 
> 
> * x<-open.ncdf("C:\\longitude.nc")*
> 
> *get.var.ncdf(x,âlongitudeâ)*
> 
> 
> 
> Result
> 
> 
> 
> *          [,1]      [,2]      [,3]*
> 
> *[1,] -111.8336        NA -111.8336*
> 
> *[2,] -111.8336 -111.8336        NA*
> 
> 
Russ Rew                                         UCAR Unidata Program
address@hidden                      http://www.unidata.ucar.edu



Ticket Details
===================
Ticket ID: YLU-405033
Department: Support netCDF
Priority: Normal
Status: Closed

NOTE: All email exchanges with Unidata User Support are recorded in the Unidata inquiry tracking system and then made publicly available through the web. If you do not want to have your interactions made available in this way, you must let us know in each email you send to us.