___   __  __     _                    
 / _ \ / _|/ _|___| |__   ___  _ __ ___ 
| | | | |_| |_/ __| '_ \ / _ \| '__/ _ \
| |_| |  _|  _\__ \ | | | (_) | | |  __/
 \___/|_| |_| |___/_| |_|\___/|_|  \___|

       ____                                        _             
      / ___|___  _ __ ___  _ __  _ __ ___  ___ ___(_) ___  _ __  
     | |   / _ \| '_ ` _ \| '_ \| '__/ _ \/ __/ __| |/ _ \| '_ \ 
     | |__| (_) | | | | | | |_) | | |  __/\__ \__ \ | (_) | | | |
      \____\___/|_| |_| |_| .__/|_|  \___||___/___/_|\___/|_| |_|
                          |_|                                    


The compression techniques used in the Offshore Compact service are proprietary. Top secret. Its strictly on a need to know basis.

The most important point to be understood is that: the compression techniques developed for this project work. In fact, they work very, very well.

Here is the table of compression examples presented on the main page:

NameOriginal size
(bytes)
Compact size
(bytes)
Saved
063544.ww3_wind_3.grb15,7447,59352%
093948.ww3_wind_5.grb98,15244,39155%
20151001_002917_.grb41,08711,54272%
ECMWF_20180507_12.grb36,89813,76263%
GFS.050.20190113.12.grb2132,16755,71658%
GFS.075.20190113.12.grb266,39628,88856%
GFS.100.20190113.12.grb243,89018,31658%
GFS20160511040500755.grb12,9406,50650%
GFS_20181115_00.grb26,49612,70652%
PWC_20160924_09.grb63,99228,72955%
WW3.20180813.06.grb229,4545,60581%
gfs20180802210007058.grb6,8383,50749%
gfs20180916065401993.grb16,8247,50555%
gfs20190110185803667.grb27,60212,68254%

When you click into one of the files, you will see more detail. For example:

Original GRIB file:GFS20160511040500755.grb
Contents:PRMSL, UGRD, VGRD
Grid:44S 32S 176W 152W
Grid size:17 x 9 = 153 points
Resolution:1.5° x 1.5°
Original size:12,940 bytes
gzip size:9,856 bytes
bzip2 size:10,378 bytes
Offshore Compact size:6,506 bytes
Offshore Compact savings:50%, 6,434 bytes
Offshore Compact file:GFS20160511040500755.lgrb

This file was downloaded while offshore on a passage between New Zealand and Hawaii. It came from Saildocs, which is a well respected provider of GRIB data worldwide. The file was downloaded using Sailmail through a SSB/Pactor modem connection. This file size was typical for the files I was downloading on that passage (if using a satellite phone connection, larger file sizes would be more typical.)

The gzip and bzip2 file sizes are provided to give a reasonable estimate of the file size you would download when obtaining data from other providers.

As you can see, the Compact Offshore file is much smaller than the other two compression techniques.

The bottom line of this compression discussion is: the Offshore Compact files offer the best compression in the industry, by a wide margin.



Copyright © 2019 Craig McPheeters. All rights reserved.