Expedition Navigation Software 
1 of 1- kjh
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Offline - Registered: 7/16/2018
- Posts: 5
Are there GRIB sources with"complex packing" or "jpeg2000" ?
The GRIB2 file format supports various bandwidth friendly compression schemes, such as "complex packing" or "jpeg2000". In my tests, "complex 3" packing or jpeg2000 can cut the file size in half.
NOAA has various GRIB subsetting APIs ( ) that are used by Expedition, but they return a file with "simple packing" (no compression).
In my experience Predict WInd and Saildocs return GRIB1 files, which don't have compression.
Most ocean racers use Iridium or similar satellite services that are very slow (2400 bps).
Are there GRIB sources with "complex packing" or "jpeg2000" ?
- Nick
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Re: Are there GRIB sources with"complex packing" or "jpeg2000" ?
The jpeg compression arrived with Grib2 and most of the raw NOAA data seems to use it, but the NOAA interface in Exp doesn't seem to return jpeg packed data.
Saildocs and PredictWind do both send grib data in Grib1 format. The Saildocs data is often packed a little better, so the file sizes can be slightly smaller.
However, both Saildocs and Predictwind are downloaded as .bz2 files that are then compressed by Exp so the lack of jpeg compression doesn't make as much difference.
Great Circle downloads in Exp are grib2 downloads with an option for jpeg compression with grib2.
- kjh
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Re: Are there GRIB sources with"complex packing" or "jpeg2000" ?
Great Circle c'est magnifique !
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