wgrib2: v3.1.3
Changes from wgrib2 v3.1.2 to v3.1.3
Bug fix for -set_bitmap 1
Complex-packed grib files have good compression with highly
parallelized decompression. Complex packing has two ways
of storing undefined values, either in bitmap or by encoding
a special value. A bitmap takes 1 bit per grid point, and
a high resolution gfs files typically uses 3-5 bits per
grid point. So storing undefined values typically takes
25% more space than using a special value. Using a bitmap
is inefficient; however, some codes cannot handle storing
undefined as a bitmap. So some operational files from NCEP
use complex packing with a bitmap. To generate such files
using wgrib2, the option "-set_bitmap 1" has to be used.
A bug was introduced to the wgrib2 where creating complex
files with a bitmap was flawed. The calculation of the range
of the field as flawed and field was truncated to a constant
field. The "optimization" was fixed removing this bug. This
bug only affected new versions of wgrib2 when using "-set_bitmap 1".
ECMWF uses AEC compression
ECMWF is producing grib files using AEC compression. By making AEC a default option,
wgrib2 needs to be built using a recent version of CMake. Once CMake becomes a
requirement for the default build, Jasper can be replaced by the long planned
OpenJPEG for jpeg2000 support. You can still build wgrib2 without CMake but you will
have to turn off AEC and replace OpenJPEG by Jasper in the makefile. The output
files created by Jasper and OpenJPEG are not bit identical but decode to
identical numbers in my testing.
Wgrib2 v3.1.3 is still including proj4 as one of its geolocation libraries.
Removing proj4 means that aspherical-earth equal area Lambert is unsupported.
Some compilers do not support proj4 which is an old version of the Proj library.
Moving to a new version of Proj is ideal but there were some API changes.
Changes for v3.1.3
- Support for OpenMP 3.1, 4.0, 4.5, 5.0 (prior: 3.1)
- added SIMD pragmas which are used if OpenMP support them
- testing AVX2 and AVX512 enabled
- support for proj4 on Mac
- makefile fixes to compiling shared lib, OpenJPEG
- NCEP grib tables updated 4/2022.
The trade offs between using SIMD vs threading is an interesting
subject. For short loops, SIMD has no overhead and will be
faster than threading. For long loops, memory bandwidth will
limit the speed. So threading could use more memory controllers
and have a faster speed. The ideal is for the threaded section
to have loops that can be speed up using SIMD. Unfortunately
that doesn't occur that frequently.
Future Changes for v3.1.4
- integrate development with NCEPlibs: github, cmake
- until the v3.1.4 is released, the github will be used to get convert to the new workflow
- updated grib tables
- added -lvl, -set_lvl1, -set_lvl2 (low level level options)
- added more levels
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