A question for brainaid

Inscrit le : 17 Oct 2007 Messages : 57

Hello Eddie,

Following the discussions on my technical problem yesterday, I took a look at your team's web site. Impressive to put it mildly. A few questions if I may.

1. You are compiling your own rankings (http://team-yacht-treff.de/mini_transat/2/classement.html), which differ slightly from the OV ones. Could you explain why?

2. How are you getting the data to compile these rankings. Are you capturing the data feed (the positions of the boats I guess) when the OV pages are downloaded? Or some other method?

3. You are compiling pretty magnificent polars (http://team-yacht-treff.de/cgi-bin/vmg-cgi?regatta=mini_transat/2&boat=brainaid). To my knowledge, OV does not provide polar data in some handy digital format. How do you obtain the data for any wind speed then?

really just a matter of curiosity ...

Regards,

Francois

Hello Francois,

someone had to ask, I feared that. Because I am honest. Most of this is developed during long nights of boat sitting and programming to keep me awake, so I will explain what I do, but I will not tell all the details. This would be boring to most of you anyway... Wink

1. The rankings differ, because they calculate the distance to the finish line as shortest distance to the line, not as distance to the center of the finish line. The shortest distance to the finish line is defined by the great circle between the ship's position and some point on the finish line. This point is either one of the buoys or that point the above great circle passes through at right angle to the great circle defined by the two buoys. Complicated? No. Finding a solution to the problem is trivial in Gnomonic projection, where all great circles are straight lines. Tricky? Yes.

2. I download pages or images from OV and calculate positions. I have no access to the database or the ship control panels. You need to read through the OV html and javascript to understand what's going on to develop stuff like this.

3. You have multiple options to get the polar data:
- Collect enough data from your races and plot that data to see what is really calculated. Then extrapolate the collected data to the original polar data. I have done this.
- Take the polar diagrams from OV and digitize the curves. I have a tool to do this and smooth the results, I needed this for Admiralty Tide Tables. I have also done this.
- Look at http://team-yacht-treff.de/polars and recycle my results. Be smart, do this, everything else is lengthy hard work.

Answer enough? I hope...

Hmmm, this is one aspect of the name "brainaid". It is helpful to use what you have up there. I like to solve tricky things, and I like to do so at night. This helps sailing on OV... Wink

_________________
Fair winds,
Eddie - Skipper brainaid - Team Yacht-Treff - OV Mini 6.50 Race Commitee
_/) _/) _/)
The sea is lovely, dark, and deep, But I have promises to keep, And miles to sail before I sleep, And miles to sail before I sleep.

Inscrit le : 17 Oct 2007 Messages : 57

Hello Eddie,

1. More or less what I suspected. That's clearly better than the OV rankings. Very Happy

Do you also take waypoints into account?

2. Mmmm. Sounds much more tricky than point 1.

3. No much wizardry here thus. Very Happy

That is also what I do, but manually of course!!! geek

Normally it is not too much work. But for the mini transat, I had a lot of trouble with the dead angles between spi/genua for specific winds speeds between 10 and 15 kts. Thanks for the available polars.

Have a nice week-end,

Francois

I'm shocked. I believed this feature was already working. I remember some tests last season.
Eddie, you have to work hared Smile

The stranding of the SprXzzi was caused by Rudy's intensive beach promenade. I wonder what he was looking for at this brasilean beach.
_________________
Bernd

Skipper K3 (1st @ Figaro 2008, fastest boat RWC 2007/2008)
Member Team Yacht-Treff