Zezo forum: algorithm current position and speed

algorithm current position and speed

Post by Olivier92 | 2020-11-23 | 10:52:57

Hello everyone. Sorry for this very basic question to which I could not find any answer :

What wind does VR use to calculate your current position and speed ?
- its last forecast ? 4 times a day or more frequently ?
- true wind from another source ? (which one ?)

Thanks you

6 Comments

Post by zezo | 2020-11-23 | 11:39:39

It's temporal interpolation of 1-degree NOAA grib files.

Forecast is updated 4 times/day, and it's gradual update as the new data comes out of NOAA.

During the weather update window (2.5 hours) it's also a mix of the old and new gribs. But the client and server don't use the same interpolation details, so there are difference between the two. The router does not use a mix, just switches between the old and the new grib in the middle of the interval (10:30/16:30 .. UTC)

Post by Olivier92 | 2020-11-23 | 14:47:28

Thank you

Post by BooBill | 2020-11-24 | 16:18:34

That is a revelation. I was always under the impression that the router was attempting to match the interpolation that the game does.

Knowing that will be helpful in moments of panic like last night when you had vast disagreement between client, server and router.

So, bit of an academic question that occurred to me last night when I was convinced that the game had downloaded a corrupt grib file (other thread suggesting that wasn't the case). When you click the refresh button in the game it syncs the client and server and reports your new calculated position. Then presumably every subsequent movement of the boat is from that last calculated position and the game does not go back and recalculate your route at any point. Once you've reached a point that it, right? If a corrupt grib is later corrected, that wouldn't lead to a retroactive recalculation of your position?

Post by zezo | 2020-11-24 | 16:30:12

Position is never calculated retroactively by the client. It just downloads the trajectory from the server next time you enter the race.

Besides, I don't think (not 100% sure, please someone correct me if I'm wrong) the server updates the winds on the refresh button.

It only does it when entering the race. So if you stay in the race the trajectory will drift further as the cached gribs get older. Same goes for your projected track.

Overall, it's good to go to the lobby now and then, unless you like watching the zig-zags.

Post by jokap | 2020-11-25 | 02:53:45

Hi Zezo,
sorry for bothering you about this again: so during what times should the weather data in the router and in the game fully agree--as a rough estimate?
Thank you for your help! And for all the work you have already put into this project--it's awesome!
Cheers,
jokap

Post by zezo | 2020-11-25 | 05:58:17

The data should agree fully roughly half of the time ;-)

Router, game server AND game client should be perfectly in sync between:

12:00-15:30, 18:00-21:30, 00:00-3:30, 06:00: 09:30 (UTC)

Most of the other time it's also pretty close, if you don't happen to be crossing a front or some other system with a high temporal/spatial gradient.

The router switches the 12/18/00/06 grib at 10:30/16:30/22:30/04:30, so 10 minutes around that time the difference will be bigger. Before or after, depending on forecast.