Jpeg2000 Compressed Grib


Jpeg2000 produces one of the smallest grib files. The problem with
jpeg2000 is that the open source libraries are single threaded and
the algorithm is involved.  As a result, encoding and decoding
jpeg2000 is slow. NCEP has adopted complex-packing for most of its
models output because of the speed of decoding.  Parallelized decoders
can by up to 20 times faster.

Support for jpeg2000 compressed grib files can be enabled by compiling 
wgrib2 with either the Japser or OpenJPEG library.  Currently the
default is the Jasper library.

Jasper:     Pro:  long-term use by wgrib2
                  no need for CMake
                  similar perforance to OpenJPEG
                  most people use Jasper

                  compiles on my linux box at work (no cmake)
                  Jasper is used by NCEP operational codes

            Con:  support is not as good as OpenJPEG (subjective)
                  doesn't work on clang, icc, arm (?)

		  default up to wgrib2 v3.1.2

OpenJPEG:   Pro:  better suport than Jasper (subjective)
                  similar performance to Jasper
                  haven't found a C compiler that can't compile

            Con:  fewer builds using OpenJPEG
		  minor: requires CMake

                  default for wgrib2 v3.1.3+
		  the AEC library used by ECMWF requires CMake,
		  so using CMake for OpenJPEG is not a big deal.


Wgrib2 v3.1.3+ transitions from Jasper to OpenJPEG for jpeg2000 support.
My automated testing says that Jasper and OpenJPEG produce files that have
the same decoded values.


                         To Compile With OpenJPEG                  


requires cmake v3.9+ and g++ to be installed
wgrib2/decenc_jpeg.c is based on ECMWF code and licensed under 
   the terms of the Apache Licence Version 2.0

To enable, edit grib2/makefile
   USE_JASPER=0
   USE_OPENJPEG=1