$Header$ -*-text-*-

The netCDF Operators NCO version 4.7.8 have hatched.

http://nco.sf.net (Homepage, Mailing lists, Help)
http://github.com/nco (Source Code, Issues, Releases, Developers)

What's new? Version 4.7.8 contains many improvements to help convert
ESM output into CMIP6 timeseries format. In particular, ncclimo
coordinates better with ncremap when processing MPAS data and
regridding. ncpdq has a new feature to convert doubles to floats,
and raw binary output can now be byte-swapped to ease creation of
offline datasets for some models like WRF and CICE.

Work on NCO 5.0.0 has commenced "under the hood". The key leap in that 
release will be support for netCDF4 user-defined types. Printing of
netCDF4 user-defined types ENUM and VLEN is ready now (though
unsupported) with the --udt flag. 5.0.0 will contain the finished
version of that, and progress on native weight generation by ncremap.

Enjoy,
Charlie

NEW FEATURES (full details always in ChangeLog):

A. ncclimo and ncremap accept the --d2f flag to turn-on the dbl_flt
   packing map that converts double-precision to single-precision.
   ncclimo --d2f ...
   ncremap --d2f ...
   http://nco.sf.net/nco.html#dbl_flt
   http://nco.sf.net/nco.html#ncpdq

B. ncremap adds missing values to single-precision MPAS variables as
   well as double. Previously it only added _FillValue to doubles.
   http://nco.sf.net/nco.html#ncremap

C. NCO takes advantage of faster stride access in netCDF 4.6.2.
   Previously NCO used its own workaround to accelerate strides.
   It will continue to do so with older version of netCDF.

D. ncremap improves metadata annotation for Tempest monotr maps.

E. ncks provides the --bsa flag to invoke a byte-swap algorithm.
   Setting this option causes unformatted binary output (with --bnr)
   to be output in byte-swapped order relative to the host machine:
   ncks -O -v uint32_var.? --bsa=1 -b foo.bnr in_grp.nc foo.nc
   http://nco.sf.net/nco.html#bnr

BUG FIXES:

A. ncatted would exit when the -t option yielded no matches.
   This has been fixed.

B. NCO could fail to build with netCDF 4.6.2 snapshots due to a
   new way of handling the log_lvl option.
   This has been fixed.

C  ncremap could fail to execute ERWG commands when started in
   a directory in which it had no write access. Now ncremap
   invokes ERWG with --no_log to prevent ERWG write attempts
   to a (possibly write-protected) working directory.

Full release statement at http://nco.sf.net/ANNOUNCE

KNOWN PROBLEMS DUE TO NCO:

   This section of ANNOUNCE reports and reminds users of the
   existence and severity of known, not yet fixed, problems. 
   These problems occur with NCO 4.7.8 built/tested under
   MacOS 10.14.1 with netCDF 4.6.1 on HDF5 1.10.2 and with
   Linux with netCDF 4.6.2-development (20180515) on HDF5 1.8.19.

A. NOT YET FIXED (NCO problem)
   Correctly read arrays of NC_STRING with embedded delimiters in ncatted arguments

   Demonstration:
   ncatted -D 5 -O -a new_string_att,att_var,c,sng,"list","of","str,ings" ~/nco/data/in_4.nc ~/foo.nc
   ncks -m -C -v att_var ~/foo.nc

   20130724: Verified problem still exists
   TODO nco1102
   Cause: NCO parsing of ncatted arguments is not sophisticated
   enough to handle arrays of NC_STRINGS with embedded delimiters.

B. NOT YET FIXED (NCO problem?)
   ncra/ncrcat (not ncks) hyperslabbing can fail on variables with multiple record dimensions

   Demonstration:
   ncrcat -O -d time,0 ~/nco/data/mrd.nc ~/foo.nc

   20140826: Verified problem still exists
   20140619: Problem reported by rmla
   Cause: Unsure. Maybe ncra.c loop structure not amenable to MRD?
   Workaround: Convert to fixed dimensions then hyperslab

KNOWN PROBLEMS DUE TO BASE LIBRARIES/PROTOCOLS:

A. NOT YET FIXED (netCDF4 or HDF5 problem?)
   Specifying strided hyperslab on large netCDF4 datasets leads
   to slowdown or failure with recent netCDF versions.

   Demonstration with NCO <= 4.4.5:
   time ncks -O -d time,0,,12 ~/ET_2000-01_2001-12.nc ~/foo.nc
   Demonstration with NCL:
   time ncl < ~/nco/data/ncl.ncl   
   20140718: Problem reported by Parker Norton
   20140826: Verified problem still exists
   20140930: Finish NCO workaround for problem
   Cause: Slow algorithm in nc_var_gets()?
   Workaround #1: Use NCO 4.4.6 or later (avoids nc_var_gets())
   Workaround #2: Convert file to netCDF3 first, then use stride

B. NOT YET FIXED (netCDF4 library bug)
   Simultaneously renaming multiple dimensions in netCDF4 file can corrupt output

   Demonstration:
   ncrename -O -d lev,z -d lat,y -d lon,x ~/nco/data/in_grp.nc ~/foo.nc # Completes but file is unreadable
   ncks -v one ~/foo.nc

   20150922: Confirmed problem reported by Isabelle Dast, reported to Unidata
   20150924: Unidata confirmed problem
   20160212: Verified problem still exists in netCDF library
   20160512: Ditto
   20161028: Verified problem still exists with netCDF 4.4.1
   20170323: Verified problem still exists with netCDF 4.4.2-development
   20170323: https://github.com/Unidata/netcdf-c/issues/381
   20171102: Verified problem still exists with netCDF 4.5.1-development
   20171107: https://github.com/Unidata/netcdf-c/issues/597
   Bug tracking: https://www.unidata.ucar.edu/jira/browse/fxm
   More details: http://nco.sf.net/nco.html#ncrename_crd

C. NOT YET FIXED (would require DAP protocol change?)
   Unable to retrieve contents of variables including period '.' in name
   Periods are legal characters in netCDF variable names.
   Metadata are returned successfully, data are not.
   DAP non-transparency: Works locally, fails through DAP server.

   Demonstration:
   ncks -O -C -D 3 -v var_nm.dot -p http://thredds-test.ucar.edu/thredds/dodsC/testdods in.nc # Fails to find variable

   20130724: Verified problem still exists. 
   Stopped testing because inclusion of var_nm.dot broke all test scripts.
   NB: Hard to fix since DAP interprets '.' as structure delimiter in HTTP query string.

   Bug tracking: https://www.unidata.ucar.edu/jira/browse/NCF-47

D. NOT YET FIXED (would require DAP protocol change)
   Correctly read scalar characters over DAP.
   DAP non-transparency: Works locally, fails through DAP server.
   Problem, IMHO, is with DAP definition/protocol

   Demonstration:
   ncks -O -D 1 -H -C -m --md5_dgs -v md5_a -p http://thredds-test.ucar.edu/thredds/dodsC/testdods in.nc

   20120801: Verified problem still exists
   Bug report not filed
   Cause: DAP translates scalar characters into 64-element (this
   dimension is user-configurable, but still...), NUL-terminated
   strings so MD5 agreement fails 

"Sticky" reminders:

A. Reminder that NCO works on most HDF4 and HDF5 datasets, e.g., 
   HDF4: AMSR MERRA MODIS ...
   HDF5: GLAS ICESat Mabel SBUV ...
   HDF-EOS5: AURA HIRDLS OMI ...

B. Pre-built executables for many OS's at:
   http://nco.sf.net#bnr

