README.g2clib

                      Changes for wgrib2 v0.1.9.8   revised 7.2016

Wgrib2 v0.1.9.8 changes the default decoders from g2clib to an emulation
of g2clib using the internal decoders.  The g2clib decoders are now an 
optional package.

The change was precipitated by reports of segmentation faults.  The
problem was finally traced back to a repository of precompiled programs.
They were compiling wgrib2 using a precompiled official version of g2clib rather 
than using the makefile to compile a patched version of g2clib that was 
included with the wgrib2 source code.  This problem was occuring with multiple 
distributions, so the use of g2clib became a compile time and run-time option.  
You have compile with g2clib and set the option to decode using g2clib.

                      Changes for wgrib2 v0.1.9.9

The default configuration is not to include the g2clib decoders in the build.

                                 WMO Standard

The g2clib and g2lib libraries do not follow the WMO standard when encoding
and decoding non-zero constant fields when the decimal scaling is not zero .  
This is a known problem for several years.  The post-processor developers 
at NCEP work around the problem when encoding a constant field so the problem 
is not commonly encountered.   

This same problem has been found in other libraries. In one library, this
error was encountered in all the tested packing formats.  Guess that it
is easier to copy the algorithm of some faulty code than to write the
code based on the specifications.  Many centers' default is set the decimal
scaling to zero and only use the binary scaling.  By using this convention,
this problem will be avoided.

Wgrib2 internal routines either follow the WMO standard or the g2clib/g2lib
behavior on non-zero constant fields with a non-zero decimal scaling.  The
default for wgrib2 to emulate the g2clib/g2lib bug.  However, if a non-zero 
constant field with a non-zero decimal scaling is encountered, a warning 
message is given.