netcdf 4

[Huw Lewis]

From ROPP-2 DRI:

Action 9 DRI ROPP v2: 
o assess the possibility to use net cdf 4 (compile, new 
  functionalities, etc.) and present results to Steering Group.


Due date: inform SG in 2009 of results

[Huw Lewis]

With the development and release of netCDF-4.0, an enhanced but more complex dat
a model is available.  Some of the new features in netCDF-4 provide better ways
to represent observational data, new ways to represent metadata, and ways to mak
e data more self-describing.

Two important data models for netCDF are
    * the "classic netCDF model", used for netCDF-3 and earlier versions
    * an enhanced data model referred to as the Common Data Model (CDM), used for netCDF-4 and later versions. Use of CF Conventions version 1.x support the classic netCDF data model with coordinate systems and other useful abstractions.

Potential benefits for ROPP

• addition of 'string' data type.
• ability to define hierarchy of variable types, compound types (e.g. Level1b, etc)

Although the netCDF-3 data model has the virtue of simplicity, it also has significant limitations.  There is little support for data structures other than multidimensional arrays and lists.

This is thought to be sufficient for ROPP at present and in future.

D

ata providers writing new netCDF data  have a choice among two obvious alternatives and a third less obvious choice:

   1. Continue using netCDF-3 software, data model, and associated format for ma
ximum compatibility.
   2. Make use of netCDF-4 software and the netCDF-4 (HDF5-based) format for its
 new data model and performance features.
   3. Use the classic netCDF data model with the netCDF-4 format.

Current option to continue with netCDF-3 type structures. This means no code changes for netCDF required, and limits need for users to install HDF5 and zlib (only required for 'additional' netcdf4 options). However, ROPP can 'support' netCDF4 (without additional features compiled - this is actually equivalent to installing 3.6.3), as it is fully backward compatible. Thus, new users can implement ROPP with latest released version of netCDF, although there is no need for existing users to update from v3.6.3.

Have now successfully tested ROPP-3 with the netcdf.4.0 distribution. Release notes and README.deps updated accordingly.

Ticket closed as fixed.