1. Definitions

A "grib file" is a collection of grib records.
A "grib file index" is an index for the grib file, used by the netcdf-java-2.2 
library (nj22). 

If the grib file has a filename or URL "gribURL", its index file has the name 
"gribURL.gbx" . The nj22 library looks for it in the same location as the grib 
file, and when possible, creates it in the same location if it doesnt exist. It 
may create it in other locations if it cant create it in the same location as the 
grib file.

The grib file index has enough information so that nj22 can create the netcdf 
objects that represent the grib file, without having to scan the entire grib file. 


2. Grib2 file index format

Section 1 Global attributes
name = value of the attribute
name must be netcdf name (no blanks etc)
value is any string, do not quote
first attribute must be "location", with value a URL or local filename
second attribute must be "length", the file size
third attribute must be "created", with value the date string the index file was 
created
------------------------------------------------------------
Section 2 Grib records
one line for each record in the file
blank separated
ProductType Discipline Category Parameter TypeGenProcess LevelType1 LevelValue1 LevelType2 LevelValue2 ReferenceTime ForecastTime Gdskey GdsOffset PdsOffset
------------------------------------------------------------
Section 3+ unique GDS records
one section for each unique GDS in the file, sections seperated by --------- line
name = value of the attribute
must have an attribute
  Gdskey = token
which matches the Gdskey token in the Grib record line


3. Grib1 file index

Section 1 same as Grib2

Section 2 Grib Records
one line for each record in the file
blank separated

ProductType Discipline Category Parameter TypeGenProcess LevelType1
LevelValue1 255 LevelValue2 ReferenceTime ForecastTime Gdskey BmsOrGdsOffset
EndOfRecord DecScale BmsExists center subCenter table_number


Section 3+ unique GDS records, same as Grib2


4. Grib Index Version numbers

0 original version
1 Grib1 index added DecimalScale & bmsExists fields to section 2 rows
2 Grib2 data read offsets now starts at the GDS offset in the section 2 rows.
This enabled processing of Grib2 thin grids.
3 Grib1 index added field Type of Generating processed, needed for Ensemble
models.
4 Added parameters to the index GDS section ie Winds, NpProj, etc
5 Grib 1 data read offset now starts at the GDS offset in the section 2 rows.
This enabled processing of Grib1 thin grids
6 Grib 1 index now has the center, subCenter, and table numbers appended to
the section 2 rows. This enables multiple parameter tables in a model.