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 175 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:

Auckland to Fiji 2023
Welcome to Auckland and, for the fifth time in Sailonline's history, an epic race to the Melanesian island of Fiji, some 1144nm away. The iconic Steinlager 2 has traditionally been our boat of choice for this event, including in 2020, the last time we raced the course – alone, unaccompanied by a real fleet as it had been #COVID19 quarantined. Alas, this year we will again be racing unaccompanied as low entry numbers has seen the real race cancelled. Hopefully, though, some of the real sailors from the Royal Akarana YC, hosts of the real event, will be joining us online to pit their skills against ours in the ever-changing forecast winds.
Race #1675
INFO by brainaid.de
Steinlager 2 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
SYC
Race starts: Jun 03rd 01:00 Registration Open!

▶ Flash

GO TO RACE

Susan Hood Trophy Race 2023

Lake Ontario Offshore Racing (LOOR) welcomes racers to the third virtual Susan Hood Trophy race. This is a 75nm weekender on western Lake Ontario starting and finishing at the Port Credit Yacht Club (PCYC) via Niagara and Burlington, and is one of two that will count towards a special Sailonline's LOOR Series medals. As our Beneteau First 36.7 managed the course so well in previous years, we shall race her again!
Race #1690
INFOby brainaid.de
First 36.7 PARTICULARS
NAM_AWIP WX Updates:
0245 / 0845 / 1445 / 2045
Ranking: SYC - LOOR
Race starts: Jun 03rd 00:00 Registration Open!

▶ Flash

GO TO RACE

SoCal 300 2023

Here, once again, is your chance to participate virtually in a second race of the California Race Week calendar, SDYC's challenging 243nm (as the seagull flies) SoCal 300 from Santa Barbara to San Diego. With a broad range of boats entered in the real race, virtual SOLers will have to dig deep to remain competitive in our trusty Santa Cruz 52s.
Race #1674
INFO by brainaid.de
Santa Cruz 52 PARTICULARS
NAM_AWIP WX Updates:
0245 / 0845 / 1445 / 2045
Ranking: SYC
Race starts: Jun 01st 20:00 Registration Open!

▶ Flash

GO TO RACE

Cape Town to Auckland 2023
Welcome to this second RTW race 2023. It's also the June edition of this year's ocean race championship. The course is slightly different from the one sailed in 2020, which then also was part of the RTW series.
This time we will race in the IMOCA 60 foil, as in all RTW races this year. That should guarantee the fun in the South Seas in a truly tough race.
PRIZE: SMPF
Race# 1685
INFO from brainaid.de
IMOCA 60 foil Particulars
WX updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - OCCH - RTW - SUPSOL - SYC
Race starts: Jun 01st 09:00 Registration Open!

▶ Flash

GO TO RACE

CA 500 2023

To celebrate the 50th anniversary of the TransPac Ocean Race in 2019, the organisers of the California Race Week introduced a new longer distance event for line-honours machines. Popular with the largest maxi trimarans, this CA 500, 500nm from San Francisco to San Diego, repeats in 2023, and if you don’t own a maxi trimaran, Sailonline are delighted to have the honour to, for the first time, make their virtual version available to you for a quick ethereal dash down America’s west coast.
Race #1687
INFO by brainaid.de
Maxi Tri PARTICULARS
NAM_AWIP WX Updates:
0245 / 0845 / 1445 / 2045
Ranking: SYC
Race starts: May 26th 18:00 Registration Open!

▶ Flash

GO TO RACE

Lisbon to Cape Town 2023
Our second OCC race in Q2 is also our first race of a special
6-race RTW series, in IMOCA 60 Foilers, from the board of ita10267. Long bluewater legs, with the shores of the World's continents the only restriction on where you may sail, starting with a 5000nm leg from Lisbon to Cape Town. Enjoy!
PRIZE: SMPF
Race #1683
INFOby brainaid.de
IMOCA 60 foil Particulars
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - OCCH - RTW - SUPSOL - SYC
RACE CLOSE: Thursday,
June 1 at 2300 UTC.
Race starts: May 03rd 09:00 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