Facebook

Login

Support Sailonline

If you haven't already - join the SAILONLINE YACHT CLUB!

Please also consider making a donation - all amounts are greatly appreciated!

Board » Technical Discussion » Weather data compression and resolution

Posted by
hmm


Users avatar

Posts
118
Registered at
2011-11-03 13:35:22
2015-02-02 11:36:05 - Weather data compression and resolution
One of the unseen changes this year is that the weather data from server to client is now compressed. (Actually all data transfer which was not yet compressed is now)

In practice this means, that the size of the weather data transferred over network has decreased by about 60%.

Because of this, for the SWR Leg 4 from Sanya to Auckland we are using higher 1 degree weather resolution (the wind data points are in 1x1 degree grid).

Previously we have usually used 2 degree resolution for ocean races, so this means we have 4 times more weather data. I hope this change adds to the accuracy of the simulation by picking smaller changes in the weather more easily.

In practice, the transferred weather size has increased to 1.6 times that it would have been previously. (compressed data is 40% of uncompressed size but data is now 4 times bigger, 0.4*4 = 1.6).

The time for loading the weather data is then bit longer than before, but I hope that the finer resolution outweights that. After all the weather data is loaded only once in starting of the client and then once every 6 hours.

As Leg4 is now open for practice, please give your feedback about the change, both negative and positive.
Posted by
Zembu


Users avatar

Posts
41
Registered at
2008-12-15 20:58:27
2015-02-02 14:29:42 - Re: Weather data compression and resolution
Hi hmm, I am wondering if the change is the reason that now for Sanya to Aukland, when loading the grib into Bluewater, the following report appears;
"The following errors occurred while loading C:/SOL/Races/
weather_100_global_gfs_20150201_1627.grb Attempt to add Grib Sequencies anyway? "Only read 18904 out of 19068 bytes for EntireMsg (offs=1029672)""???
Posted by
hmm


Users avatar

Posts
118
Registered at
2011-11-03 13:35:22
2015-02-02 17:52:08 - Re: Weather data compression and resolution
I would more guess that the problem is the weather data in the grib crossing international date line, but I am no expert in BWR as I don't use a router..
Posted by
ita10267


Users avatar

Posts
88
Registered at
2008-12-29 10:33:09
2015-02-05 09:42:17 - Re: Weather data compression and resolution
yes,
the problem is that gribs produced on brainaid site are defined to be continous when crossing greenwich, so they present discountinuity in Longitude on the IDL (transition from -180 to 180). Bluewather and some other grib viewing softwares don't know how to handle this. If you fetch gribs directly from NOAA you can "tweak" this by moving the discontinuity to Greenwich (transition from 0 to 360) in order to cross the IDL with no problems.

hope that this clarifies the matter

--- Last Edited by ita10267 at 2015-02-05 09:42:36 ---
Posted by
Zembu


Users avatar

Posts
41
Registered at
2008-12-15 20:58:27
2015-02-08 23:03:19 - Re: Weather data compression and resolution
ITA, Yes, I am aware of the fact that Bluewater needs to have part of the grib "disabled", when the grib straddles the dateline. This is not a problem and I do not think that it is the reason why Bluewater signals that the file is smaller than expected. There is no need to change the discontinuity to Greenwich. One merely uses the grib manager in Bluewater to not use the unwanted part for routing. When I have used Bluewater in the past when the grib straddles the dateline, I don't recall noticing the following from Bluewater;
"The following errors occurred while loading C:/SOL/Races/
weather_100_global_gfs_20150201_1627.grb Attempt to add Grib Sequencies anyway? "Only read 18904 out of 19068 bytes for EntireMsg (offs=1029672)""???

Further to the above, as of approximately 10th/11th Feb 2015, the above message is no longer displayed by Bluewater. From discussion noted in the chat, I surmise that Brainaid has fixed the problem.
--- Last Edited by Zembu at 2015-02-09 17:02:42 ---

--- Last Edited by Zembu at 2015-02-11 17:06:30 ---
Posted by
Kipper1258


Users avatar

Posts
263
Registered at
2015-06-18 22:08:49
2016-03-17 12:14:53 - Re: Weather data compression and resolution
ita10267 said @ 2015-02-05 09:42:17:
If you fetch gribs directly from NOAA ...

ita, I'm wondering if you have the details on how to do that. I've had a look at the NOAA site but would not know where to start. Is there a simple way to pull the gribs from NOAA or a script available to do that?

Thanks

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Cross the Convergence 2026 - Masirah to Chagos


Having crossed, re-crossed and re-re-crossed the Convergence Zones of the Pacific and the Atlantic, we now face our second crossing of the Convergence Zone of the World’s third great equator-spanning sea, the Indian Ocean, taking us from the channel between Masirah Island and the Oman mainland to the Chagos Archipelago. It’s 1900nm and we’ll be sailing our very fine Archer 78, and won’t mention that both locations (of departure and arrival) are heavily militarized and the why’s and what next’s concerning that – mindful as always of SOL Netiquette.
Race #1988
INFOby brainaid.de
Archer 78PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: CCZ - SYC
Race starts: Oct 02nd 18:00 Registration will open soon
▶ Flash
GO TO RACE

Carib Rum Run 2026


Ahoy, ye landlubbers and seasoned salts! Welcome back to Sailonline’s legendary Carib Rum Run, perfectly timed to kick off on International Talk Like a Pirate Day, 19 September!

This year, we command the magnificent Falkun—the ultimate high-tech superyacht modeled after the iconic Maltese Falcon. This 1759nm slalom takes us through the Caribbean’s rum islands to plunder barrels from local distilleries and deliver them to the rum-parched sands of Cancun.

Join SYC before the finish to disguise yer boat with a pirate name for this race only. Hoist the sails, sharpen yer cutlasses, and plot your winning course!
Race #2060
INFO by brainaid.de
Falkun PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Sep 19th 05:00 Registration Closed
▶ Flash
GO TO RACE

Shearwater - Rio de la Plata to Irish Sea 2026

Welcome to the fourth leg of our MIG series. This time we're racing the Sooty Shearwater on their migration from the breeding grounds in South America to the northern Atlantic. This is also part of our Ocean Championship, and as such the third race of OCQ3 2026. This race will be sailed in our Gunboat 90. Race #2055
INFO by brainaid.de
GunBoat 90 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
OCQ3 - OCCH - SYC - MIG
RACE CLOSE: Thursday,
October 1 at 2300 UTC.
Race starts: Sep 02nd 11:00 Registration Closed
▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member KaSToR
  2. Sailonline Yacht Club Member CriticalHippo
  3. Sailonline Yacht Club Member WRmirekd
  4. Sailonline Yacht Club Member rafa
  5. Sailonline Yacht Club Member cdhinman
  6. Sailonline Yacht Club Member Panpyc
  7. Sailonline Yacht Club Member rumskib
  8. Sailonline Yacht Club Member rthinman
  9. Sailonline Yacht Club Member BRENTGRAY
  10. Sailonline Yacht Club Member Sax747

View full list

Series

Mobile Client

SYC members have the benefit of access to our mobile/lightweight web client!

The mobile client