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 » How to handle wheatherdata differences ?

Posted by
Armchairsailor


Users avatar

Posts
6
Registered at
2012-03-22 09:35:22
2015-09-29 02:43:55 - How to handle wheatherdata differences ?
In my current position in the Timed transat
LAT 49°14.3747'LON W 022°55.8096'
DATE 2015-09-29 TIME 02:30:08
the wind information in the client
differs from the wind information in the gribviewer, which uses the file from
brainaids site:
"weather_186_global_gfs_20150928_2227.grb"

client TWD 122.34° TWS 2.82KT
gribview TWD 120 TWS 5.3KT

Meanwhile I have read that there are differences. The effect is that my routing software sends me in the wrong direction.
How do other SOL users handle this situation ?

--- Last Edited by Armchairsailor at 2015-09-29 08:17:01 ---
Posted by
kroppyer


Users avatar

Posts
347
Registered at
2010-02-05 15:25:55
2015-09-29 17:42:44 - Re: How to handle wheatherdata differences ?
The difference is there because sol uses a different interpolation method than your router/grib viewer does. Some routers/viewers offer multiple interpolation methods. If your viewer/router has that option, you can experiment with the different methods, see which one is closer.

In general, this problem occurs most often in large wind shifts (spacial, or over time). So usually it's in the light winds ("blue goo") that the router is off. I believe most people cope with that by hand steering as much as possible in the blue goo, and even better: avoiding the blue goo.

You could consider it as part of realism: winds are not always as they are in your router, especially not in light, shifty conditions.

If you're really bothered by this, you could try different routers/viewers to see which matches sol the closest, and you could write your own/adapt an existing one.
Posted by
Armchairsailor


Users avatar

Posts
6
Registered at
2012-03-22 09:35:22
2015-09-30 04:31:59 - Re: How to handle wheatherdata differences ? thnks
Tnks kroppyer for your reaction.
It is as you say. This resembles reality.
I was attrackted by the high wind speeds of the depression, but development of it changed, as usual. I had no chance at all to avoid the blue gue afterwards.
I am having thoughts to write my own router. But that won't change reality.
Posted by
Kipper1258


Users avatar

Posts
235
Registered at
2015-06-18 22:08:49
2015-10-12 22:23:32 - Re: How to handle wheatherdata differences ?
kroppyer said @ 2015-09-29 17:42:44:
...you could write your own/adapt an existing one.
Kroppyer, where can we source the SOL server interpolation code to see how it works / replicate it in other tools? It does not seem to be posted anywhere (at least Google can't find it)

Thanks
Posted by
kroppyer


Users avatar

Posts
347
Registered at
2010-02-05 15:25:55
2015-10-13 13:35:49 - Re: How to handle wheatherdata differences ?
Server code is not published, all we (solers) can do is measuring and fitting. I've done this in the past, didn't get perfect results but to me it's close enough for now.

In this thread I explain my findings, and I link to a post from Jakob (who, together with kalle, wrote most of the server-side code) explaining some more about the interpolation.

EDIT: fixed link (you should'be said it didn't work! :)

--- Last Edited by kroppyer at 2015-10-20 14:23:32 ---
Posted by
outlaw


Users avatar

Posts
33
Registered at
2012-06-01 13:37:55
2015-10-13 18:19:01 - Re: How to handle wheatherdata differences ?
Interpolation in space is simple bilinear. In time is a 'shape function', apparently 3*t^2-2*t^3. So you get
v(19:00)=.26*v(18:00)+.74*v(21:00)

For the polar use the 'detailed csv', where TWS interpolation is again linear. Not sure about TWA, but it's 1 degree resolution, *shrug*.
Posted by
kroppyer


Users avatar

Posts
347
Registered at
2010-02-05 15:25:55
2015-10-13 23:04:01 - Re: How to handle wheatherdata differences ?
For interpolation on the polar, I used the same method in SPINNACER as AGage used in his SOL Polar Explorer. See class AGage.PolarExplorer.Interp here.


AGage comments (in the code) "Interpolate as on sailonline.org", so I guess he did exactly the same as sol does.

I'm not sure if this code performs linear interpolation, but I wouldn't know what else. I'm pretty sure it's at least close to linear interpolation. Also "linear" looses meaning when you use polar coords... but now we're talking minor differences. Like outlaw says: *shrug*

Please login to post a reply.

Races

Next Race: 00d 00h 00m

Current Races:

Regata dell’Accademia Navale 2025

Welcome to Sailonline’s first partnership with the City of Livorno, in cooperation with the local yacht clubs and the Italian Navy, to offer you the online opportunity to race the Regata dell’Accademia Navale. 630nm in length, starting and finishing in Livorno, the race takes you the length and breadth of the Tyrrhenian Sea via Porto Cervo and Capri. Online, you will be sailing a Class 40, which should keep you well in with the top of the real-life fleet which we will be tracking on screen!
Race #1902
INFO by brainaid.de
Class 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Apr 26th 10:00 Registration Open!

▶ Flash
GO TO RACE

Gulf of St Lawrence 2025


The Gulf of St. Lawrence, with one of the largest and deepest estuaries in the world, will be the site of a completely new race in SOL. Our Melges 40 will take us 950 nm from Bathurst in Baie des Chaleurs around the islands of Anticosti, Pelee and Prince Edward admiring beautiful landscapes along the way. Fair winds.
Race #1910
INFO from brainaid.de
Melges 40 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
ARQ2 - ARCH - SUPSOL – SYC
Race starts: Apr 21st 17:00 Registration Open!
▶ Flash
GO TO RACE

Transat à Deux 2025

Above you see a single-handed sailor semi-foiling his Beneteau Figaro III to the horizon. It is in fact Ireland’s Sailor of the Year and the overall winner of last year’s Solitaire du Figaro, Tom Dolan. Somehow, we got our hands on a polar for the Class, and rather than trying to surreptitiously track Tom and his mates in the 2025 edition of the Solitaire, sailing rather-short, single-handed legs across the Celtic Sea and Biscay, we thought we’d see how our virtual craft would fare on the Class’s double-handed 3900nm Trans-Atlantic, from somewhere in Brittanny to somewhere in the Caribbean via somewhere in the Canaries. Allez, mes braves!
Race #1901
INFOby brainaid.de
Figaro III foil PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Apr 20th 11:00 Registration Open!
▶ Flash
GO TO RACE

Gladstone Ports Corporation Brisbane to Gladstone Yacht Race 2025


Sailonline is thrilled to partner with the Queensland Cruising Yacht Club for the 2025 Gladstone Ports Corporation Brisbane to Gladstone Yacht Race. This 308 nautical mile offshore classic takes our fleet from Brisbane to Gladstone along Australia's stunning east coast. Racing in high-performance Cookson 50s, SOLers will face shifting winds and tactical decisions at every turn. It’s time to test your skills in one of Australia’s most iconic yacht races. See you on the start line!
Race #1904
INFO by brainaid.de
Cookson 50 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC
Race starts: Apr 18th 01:00 Registration Open!
▶ Flash
GO TO RACE

Bahamas and Back TIMED Race 2025

Welcome to sunny South Florida for this race that has us crossing the Gulf Stream twice. We depart from Palm Beach for a short run over to Freeport, Bahamas then it’s on to Miami before heading to the finish line back in Palm Beach. This is a TIMED race, so you may RE-REGISTER HERE to try again, after finishing a run. You will have 13 days and 11 hours to test your skill and decision making after the race opens.
Race #1911
INFO by brainaid.de
Santa Cruz 70 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking:
TRQ2 - TRCH - SUPSOL - SYC
RACE CLOSE: Saturday,
26 April at 23:00 UTC
Race starts: Apr 13th 12:00 Registration Open!
▶ Flash
GO TO RACE

Sinbad by Balloon 2025 - Toamasina to Baia de l'Oiseau


You may recall that when last we visited Madagascar in the company of Sinbad, the Sultan commanded our intrepid inspirator to seek out fabled islands where in Summer the sun barely set. We did and we returned but the Sultan wasn’t happy with Sinbad’s report, so here we go again, now by SOL Balloon instead of sailing vessel. Expect to be in the air for at least 2100nm and depending on how the wind brings us, anything between two weeks and two months before we shall descend at the Sultan’s given coordinates!
Race #1884
INFOby brainaid.de
SOL Balloon PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: SYC - SBB
Race starts: Apr 09th 11:00 Registration Closed
▶ Flash
GO TO RACE

Valparaiso to San Francisco 2025

Get ready for an exhilarating new challenge as we set sail on the fourth leg of the 2025 Ocean Championship Series! Following in the 19th century footsteps of Isabel Allende's heroine, Eliza Sommers, 'Daughter of Fortune', this all-new route takes us across the vast eastern Pacific, from Valparaíso, Chile, to San Francisco, California - a 3500nm journey of endurance, strategy, and pure sailing adrenaline. This leg will be raced aboard the powerful Rapido 60, pushing sailors to their limits as they navigate the open ocean. Do you have what it takes to conquer the Pacific? Join us and put your skills to the ultimate test!
PRIZE: SMPF
Race #1900
INFO by brainaid.de
Rapido 60 PARTICULARS
WX Updates:
0430 / 1030 / 1630 / 2230
Ranking: OCQ2 - OCCH - SUPSOL - SYC
Race starts: Apr 07th 11:00 Registration Closed
▶ Flash
GO TO RACE

Melbourne Osaka Cup Double-Handed Yacht Race 2025

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 this year is such a year. So, this year’s online version is in sync with the Melbourne Osaka Cup 2025 organised by the Ocean Racing Club of Victoria (ORCV), and the Sandringham (SYC) and Osaka Hokko (OHYC) yacht clubs. We’ll be racing the well-known First 40, a popular size of boat which should be a good match for many of the boats entered in the real race. With the doldrums unavoidably lying across our course, 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 CLOSE: Wednesday,
April 23 at 2300 UTC.
Race starts: Mar 16th 06:00 Registration Closed

▶ Flash
GO TO RACE

Go to race archive

SYC Ranking

  1. Sailonline Yacht Club Member WRmirekd
  2. Sailonline Yacht Club Member Patrick70119
  3. Sailonline Yacht Club Member KaSToR
  4. Sailonline Yacht Club Member CriticalHippo
  5. Sailonline Yacht Club Member vida
  6. Sailonline Yacht Club Member FreyjaUSA
  7. Sailonline Yacht Club Member rafa
  8. Sailonline Yacht Club Member bonknhoot
  9. Sailonline Yacht Club Member Kipper1258
  10. Sailonline Yacht Club Member rumskib

View full list

Series

Mobile Client

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

The mobile client