Sailonline.org - Online Sailing

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!

Tweets by @sailonline

Board » Technical Discussion » Weather data compression and resolution

Posted by hmm 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 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 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 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 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 Posts 179 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:

Jakob's Birthday BBQ Race 2024

Sailonline had two founders and Jakob, the more senior of the two, has his birthday in April which we always like to celebrate with a race through the Stockholm Archipelago from Revengegrundet Lighthouse to his mooring at Baggensfjärden. Traditionally also, like other celebrations this time of year, this feast has been “moveable”, so on this occasion we will be racing on a Wednesday in one of our latest high-performance 40-footers, the Carkeek 40. Please join us then for this always tricky 30nm race. Grattis på födelsedagen Jakob!
Race #1794
INFO by brainaid.de
Carkeek 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Apr 20th 14:00 Registration Open!

▶ Flash

GO TO RACE

Melbourne to Osaka Prelude 2024

Welcome once again to what these days is Sailonline’s almost annual virtual Melbourne to Osaka Yacht Race. In real life, this double-handed 5500 nm race between these two sister cities, one deep in the southern hemisphere, the other high in the northern hemisphere, is run every four to five years, and is planned to be held again in 2025, so this race is a Prelude in partnership with the Melbourne Osaka Cup 2025 organising committee collaborating with the Ocean Racing Club of Victoria (ORCV), and the Sandringham (SYC) and Osaka Hokko (OHYC) yacht clubs. On this occasion, we’ll be racing the well-known First 40, a popular size of boat for a long-distance double-handed race. With the doldrums unavoidably lying across the track, you can expect to be at virtual sea for at least a month!
Race #1669
INFO by brainaid.de
First 40 Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Apr 20th 00:00 Registration Open!

▶ Flash

GO TO RACE

St Nazaire Chasse TIMED Race 2024

Welcome to a "chasse" (hunt) from St. Nazaire to La Baule on the west coast of France! This race was designed by SOLer FR_flouflou in 2010. The KER 40 was introduced to SOL in 2016 by SOLer psail, and the Sol-KER was a welcome addition to SOL’s fleet of 40- footers, as it was to the IRL Ker fleet of eponymous - like KERonimo, KukuKERchu and Ice BreaKER. This is a TIMEDrace, so you may RE-REGISTER HERE to try again, after finishing a run. You will have 13 days and 11 hours to show your skill and decision making after the race opens.
Race #1797
INFOby brainaid.de
Ker 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ2 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
27 April at 23:00 UTC
Race starts: Apr 14th 12:00 Registration Open!

▶ Flash

GO TO RACE

The Beagle in the Straits of Magellan 2024

Both before and after visiting the Falkland Islands, the Beagle extensively explored the south eastern coast of South America, hither and thither, from north of the Rio Plate to the tip of Tierra del Fuego, but it was not till the end of June 1834 that the ship made it into the Pacific Ocean, transiting via the Straits of Magellan. Online in 2024, the choice is yours - passage the strait or round the cape; 400nm or more in your Class B Tall Ship.
Race #1753
INFOby brainaid.de
Tall Ship Class B PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SVF - SYC
RACE CLOSE: Sunday,
April 21 at 2300 UTC.
Race starts: Apr 09th 13:00 Registration Closed

▶ Flash

GO TO RACE

Cape Town to Auckland 2024

Welcome to the second leg of this Round The World series 2024. It's also the April edition of this year's ocean race championship. The course is the same as the one sailed in 2023, but this year we sail the iconic Swan 65, as suggested in the concluding RTW race last year.
Prepare yourselves for an epic 30-day journey, navigating through the unpredictable waters of the South Seas. It's essential to take care of provisioning to ensure a smooth and enjoyable race experience. With the longer duration, we anticipate plenty of opportunities for camaraderie, competition, and unforgettable memories.
PRIZE: SMPF
Race# 1789
INFO from brainaid.de
Swan 65 PARTICULARS
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - RTW - OCCH - SUPSOL - SYC
Race starts: Apr 01st 11:00 Registration Closed

▶ Flash

GO TO RACE

Go to race archive

SYC Ranking

View full list

Series

Mobile Client

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

The mobile client