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NUWG NetCDF Conventions Information

What is the NUWG?

When is the next meeting?

Topics for discussion:

• We decided to revisit the conventions for surface and upper-air data, now that both Unidata and FSL have written decoders to produce netCDF files and have adapted and modified the conventions to work better with these decoders. This topic may be appropriate for email discussions. Dave Osborn of FSL has supplied the following FSL CDL files for NUWG consideration:
  • buoy
  • sao
  • raob
  • mesonet
  • lightning
  • rass 6 min
  • rass hourly
  • profiler 6 min
  • profiler hourly
  • airmet/sigmet (still being tested)
• In light of our discussions with John Caron of NCAR, we may consider a "simple" generalized parameterization for standard navigations/projections.
• (Tabled from last meeting) Russ Rew will present a discussion of an alternative to the NUWG dimension attribute convention involving multidimensional coordinate variables instead. The multi-dimensional coordinate variable solution has some advantages and limitations when compared with the dimension attribute convention. We may also discuss a proposal for keyed access to netCDF data that can be implemented over either of these alternative conventions.

When was the last meeting?

The most recent meeting was 30 August 1995. Topics discussed included:

• We considered the re-mapped satellite case, most similar to the gridded data case, and the navigation variables conform to the gridded data conventions. Andrew Sundelin presented an example CDL for the remapped AWIPS/ISPAN satellite data. The NUWG group approved this example, with the addition of a nav_model="GRIB1" variable to specify the navigation model, deletion of redundant "missing_value" attributes, and addition of valid_min and valid_max attributes to the image variable.

• We discussed whether the default for byte data should be signed or unsigned. Current documentation of the horribly-named signedness attribute says the default is unsigned, but Harvey Davies has pointed out that this conflicts with the current default _FillValue for netCDF byte data, which is -127. For now, data providers may use valid_min and valid_max attributes to indicate the range of values for byte data.

• We discussed possible values for the nav_model navigation variable. for parameterizations of georeferencing information. Previously we had considered the WMO GRIB edition 1 GDS specification and the U.S. Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata available in text, Postscript, or PDF forms.

  Russ Rew promised to send information on the new GeoTIFF specification.

  GeoTIFF represents an effort by over 140 different remote sensing, GIS, cartographic, and surveying related companies and organizations to establish a TIFF based interchange format for georeferenced raster imagery.

  Code to build libgeotiff is freely available, including Niles Ritter's public-domain GeoTIFF key parsing library, example programs, and makefiles.

  Someone should look at this and evaluate whether GeoTIFF is useful for a navigation model of our georeferencing conventions. We discussed whether it would be better if we recommended a single navigation model in the NUWG conventions, rather than providing a list of usable navigation models, thus requiring applications or the udnav library to be able to handle all of them.

• We decided to table until the next meeting a discussion of a new proposed convention for coordinate reference variables (John Caron's terminology) that has some advabntages over the current dimension attribute convention. Details will be made available on a web page soon.

Current Status

• Current NUWG Email Threads
  • Georeferenced gridded data conventions
  • Radar data conventions

• Current draft of "Report on the NetCDF Users Working Group"

• General Conventions approved by NUWG

  See next four bullets for specific conventions by data type

• Conventions for Surface Observations
  • Documentation of the SAO conventions
  • Sample CDL for SAO's

• Conventions for Upper Air Observations
  • Documentation of the upper air conventions
  • Sample CDL for upper air observations

• Conventions for Georeferenced Gridded Data
  • Summary of georeferenced grid conventions discussed 2/15/95 UPDATED 4/21/95
  • Current email thread on Georeferenced gridded data conventions
  • Unidata's draft CDL for the RUC/MAPS model
  • FSL's updated draft CDL for the MAPS model
  • More information about grid conventions

• Conventions for Satellite Data -- The NUWG has been working on the un-remapped satellite conventions. Below you will find an example CDL and the first draft of a summary document. The NUWG encourages comments and questions about these conventions (nuwg@unidata.ucar.edu).
  • First draft of un-remapped satellite conventions 5/2/95
  • Sample FSL satellite CDL (un-remapped) 4/25/95

  These sample CDLs come from around the community. The NUWG has not explicitly endorsed any of of these samples. They are referenced here for illustrative purposes.

  • Sample CDL for AVHRR data
  • Sample CDL for DMSP high resolution data
  • Sample CDL for mapped data
  • Sample CDL for SVISSR data
  • Sample CDL for GOES data
  • Sample CDL for Sharp AVHRR

• Other Conventions
  • COOP Conventions
  • ICSPAT Conventions
  • NCAR-RAF Conventions
  • PMEL-EPIC Conventions
  • Old outdated Unidata Conventions

• Summaries of Past Meetings

Who are Susan Jesuroga and Peggy Bruehl?

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