Adding bounds variable to netcdf file

Question

I would like to add latitude bounds to an existing netCDF file. See http://www.cgd.ucar.edu/cms/eaton/netcdf/CF-20010629.htm#bnds for definition of bounds.

Is there a command that can add bounds automatically? I am open to any solution using nco or netCDF4 or cdms toolkit. However, I would prefer it to be a post processing solution.

Answer 1

Add bounds to an existing coordinate like this:

ncap2 -O -s 'crd@bounds="crd_bnds";defdim("bnds",2);crd_bnds[$crd,$bnds]=0.0;*crd_dff=0.5*(crd(1)-crd(0));crd_bnds(:,0)=crd-crd_dff;crd_bnds(:,1)=crd+crd_dff;' in.nc out.nc

This yields

zender@aerosol:~$ ncks --cdl -v crd ~/foo2.nc
netcdf foo2 {
  dimensions:
    bnds = 2 ;
    crd = 10 ;

  variables:
    int crd(crd) ;
      crd:bounds = "crd_bnds" ;

    double crd_bnds(crd,bnds) ;

  data:
    crd = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ;

    crd_bnds = -0.5, 0.5, 0.5, 1.5, 1.5, 2.5, 2.5, 3.5, 3.5, 4.5, 4.5, 5.5, 5.5, 6.5, 6.5, 7.5, 7.5, 8.5, 8.5, 9.5 ;

} // group /

Here the coordinate is named "crd", and the bounds are named "crd_bnds". The formula for the bounds values can be simple when the coordinate changes by a fixed value (as above), or more involved to account for variable spacing (exercise for reader). We will add an ncap2 function to do this automatically in the near future.

cz