Re: 980218: NetCDF

>To: <address@hidden>
>From: "vb" <address@hidden>
>Subject: NetCDF
>Organization: Office International de l'Eau
>Keywords: 199802181500.IAA08108

Hi Vincent,

> I would like to get a general presentation of the NetCDF format. Do you
> have it in a PDF or Word file ?

Unfortunately, I don't have anything very recent.  There is a
presentation on netCDF 2.4 with some plans for netCDF 3 available in
HTML form at

   http://www.unidata.ucar.edu/packages/netcdf/conf95/NetCDF/talk.html

Another slightly more recent talk about NetCDF Status and Plans is
available at

   http://www.unidata.ucar.edu/packages/netcdf/iita/stat1.html

The release notes for netcdf 3.3.1 contain quite a bit of updated
information:

   http://www.unidata.ucar.edu/packages/netcdf/announce-3.3.1.html

Since then, we have also made available a pure Java version of netCDF
for testing, but we haven't gotten much feedback on it yet:

   http://www.unidata.ucar.edu/packages/netcdf/java/

I also made a presentation in February 1997 on "Unidata's netCDF
Interface for Data Access: Status and Plans", but I used Aldus
Persuasion 3.0 on a Macintosh, and thus only have it available in that
form or as PICT, Scrapbook, or Persuasion Player formats.  I've appended
the text outline from that talk, and could make it available in PDF form
with some work (importing it into Persuasion 4.0 and then exporting that
as PDF), in case you are really interested, but there's not much more
than the text in the appended outline.

--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
address@hidden                     http://www.unidata.ucar.edu

Unidata's netCDF: Status and Plans
        Russell K. Rew and Glenn P. Davis
        UCAR Unidata Program
        Thirteenth IIPS Conference
        Long Beach, California
        February 1997

What is netCDF?
        - Data model, software, and format
        - Insulates users, applications, and data from
                machine architectures
                format details
        - Provides data that is
                self-describing
                portable
                directly accessible
                appendable

Who Uses netCDF?
        - In widespread use
        - Atmospheric sciences, oceanography, recently some other
          disciplines (seismology, physics, chemistry, medicine, ...) 
        - Packages with netCDF access include DDI, DODS, EPIC, FAN,
          FERRET, GEMPAK, GMT, GrADS, HDF, IBM Data Explorer, IDL,
          LinkWinds, MATLAB, NCAR Graphics, ncview, PolyPaint+, PPLUS,
          PV-Wave, SciAn, Zebra ... 
        - Language interfaces include C, Fortran, C++, perl, Python,
          Java, ... 
        - Popularity means changes must be implemented carefully

What is the Status of netCDF?
        - In Transition from version 2 to version 3
        - Current:      version 2.4.3 released August 1996
        - New:  version 3 in alpha testing, release imminent
        - Planned:      version 4 being specified
        - Bad news:     version 4 requires a new file format
        - Good news:    netCDF and HDF may share same file format

What's New with netCDF 3?
        - Completely rewritten in ANSI C
        - Improved
                performance
                shared access to data
                documentation: separate C and Fortran user guides
                C interface: type-safety, automatic type conversions
                Fortran interface: readability, automatic type conversions
        - Unchanged
                File format (still using original format designed in 1988)
                Support for version 2 interfaces

What Limitations Remain?
        - netCDF 4 will eliminate some limitations
        - Lack of packed data types for low-resolution data
                Currently supports characters, 8-, 16-, and 32-bit
                integers, 32- and 64-bit floating  point 
        - 2 Gbyte limit on file size
        - Can append along only one dimension
        - No links to external data in other files
        - Other requested features: nested structures, ragged arrays,
          built-in georeferencing, keyed access by coordinate values,
          ... 

What is the Status of NetCDF-4?
        - Schedule to be determined
        - New external types for packed data
        - Elimination of 2 Gbyte size limit
        - Data links
        - New format required
        - Other possible features: nested structures, ragged arrays,
          built-in georeferencing, keyed access by coordinate values,
          ... 

Packed Data
        - Interfaces already specified
        - New external types for packed n-bit values: n = 0, 1, ..., 32
        - Transparent to readers
        - Predefined or adaptive scaling
        - Packing and scaling parameters may vary along multiple dimensions
        - One or more special values preserved exactly

New File Format
        - Backward compatibility with current format important
        - NetCDF-4 will support reading and writing current format files
        - Cannot write packed data to current format files
        - May share format with HDF

More Information on netCDF
        - Freely available via WWW or anonymous FTP
        - For details, see http://www.unidata.ucar.edu
        - Site includes 
                Access to netCDF software
                Answers to frequently asked questions
                What's new with netCDF
                Latest on-line documentation
                Links to many packages that can access netCDF data
        - Searchable archives of support email