Zezo forum:

Post by DABurleigh | 2015-02-12 | 10:48:26

zezo,

Is it just me or is there an inconsistency in the course indicated by the text in the box that appears when you hover the mouse over a course-change dot, and that in the box when you move the mouse to superimpose a heading (red fixed or green TWA) over the route from that course change? It can be different by a few degrees and I don't know which to believe! :-(

Three explanatory screenshots from the same route calculation in this public Google+ album:
http://goo.gl/f8c7Tx

Thanks for checking it out; I now await a simple explanation which makes me feel an idiot :-)

Dave
PS. First post, so thank you for all your efforts! From curiosity I want to find out more about the maths of route optimisation, but haven't found much online so far.

8 Comments

Post by din0 | 2015-02-12 | 11:26:21

Check this out:

Post by zezo | 2013-12-21 | 09:19:14

Hmm. That's actually a feature ... for the races with interpolated winds where it's often better to sail at fixed twa. To avoid having black dot every 10 minutes I've relaxed the calculation of the angle.

With wind grids it's a bit different. The router tries tracks in 5-degree increments, so when it has to sail at 112, it actually sails at 110 for 10 minutes, then at 115 for 10 or 20 minutes and so on.

In the previous version you would see the averaged heading and that would be 112. In the current one you see the actual numbers.

I have to think a bit how to fix but still have the concept of fixed TWA in the interpolated winds. You can always use the track tool to see the actual direction and progress.

Besides, at those latitudes the great circle and the rhumb line diverge quickly enough to add 1-2 degree correction in a single wind cell.

Post by DABurleigh | 2015-02-12 | 12:37:38

Thanks. Not convinced that's it as the screenshots show it's 5 degrees out.

Dave

Post by Wetedge4 | 2015-02-12 | 18:42:37

From what I've learned.. Sometimes the "dots" are for the next cycle ie: @ 20:10 zezo wants you @ 134* with 60TWA, but in the game it's actually 20:04 so the numbers won't be correct. Make sure you refresh the game @ the timestamp of zezo to get correct heading. If you don't you will be turning early, and a lot of the time zezo will want you to turn back the other way the next cycle. Also, sometimes the heading, the TWA, and speed don't line up from zezo to game, but almost always, the TWA and speed will be in alignment. Use the track tool, if you set the GREEN TWA to what zezo wants in the "dot", the RED heading # will be correct(even if the heading in "dot" is different). Not sure how well I explained that :) Hope it helps.

It's usually only 1 degree off in "dot" heading, compared to what heading should be for certain TWA, but the track tool will show correct #s, unless you are looking at the "dot" for the next cycle in the game

Post by zezo | 2015-02-13 | 16:30:09

Dave,

What your screenshot displays is obviously not the 5-degree inconsistency because the wind direction and speed differ quite a lot.

There are three possible reasons for this:

- There is something wrong with the wind forecast. This one rarely happens (once in a month or two) but it's nice to compare the numbers between the site and the game just to make sure.

- There can be a caching problem in the browser, possibly related to wrong local computer clock. Hitting F5 would probably fix it.

- The displayed forecast is not the current one. Easiest way to make sure the wind data corresponds to the time of the popup info is clicking the black dot. This switches the arrows to the appropriate time.

Post by RickW | 2015-02-14 | 04:45:50

It is just the Dummy.
Ah, another tidbit of knowledge; a click on a black dot. Holy Cow!

Having found out here in VR that websites spew out tons of data to many users through Developer Tools; ergo VRT boat positions. Being an appliance user of computers this was an adventure into Geek World.

It had then occurred to me that data sources vary and so does the data. I see four places to verify data that competitors would like to have. These are VR operations game window, Zezo, VRT desktop and VRT's Boat Attitude. What did I miss? In all cases I have found that at least two sources verify a navigational question. It is like the Quadratic Equation, anything missing can be sourced. The same applies to TW, TS, BS and TWA with the Polar chart involved. I am relying on common sense and could be out to lunch but finding things that work or add up.

I have not been able to use the many features of VRT because there is nothing current to guide me (a manual, if you will) but it is a good source for planning data as a calculator and marking places for navigation. Yeah, I know, crude, but then some muddle along.

Probably the best calculator out there is Paco Tool but there is no manual for that either in current time in an international language. Translation has not helped

What may have been the best site of all, vrtoutoulz is gone but reference everywhere on the web to a dead end.

The Point: verification of what you are looking at when it is important to competition and you have only common sense and math to guide you. VR is not going to help, trust me.

So, the questions here can be solved this way. Zezo is a wonderful resource and guide to suggested routes but it, like all data sources, need to be verified for your competitive comfort.

As a casual gamer I am pleased with the attitude of this forum and the features of Zezo for VR sailing. I am ambivalent about VR.com but carry on with hopes common sense there will arrive.

The click on the black dots tells me that Cvetan is more than a programmer.

Forgive me my length of wind...

Post by DABurleigh | 2015-02-19 | 20:45:44

Many thanks to Wetedge4 & zezo (Cvetan). I read your posts soon after you made each of them but didn't acknowledge at the time :-(

Maybe I just naturally absorbed them because I haven't noticed similar since!

I'm enjoying how the changing winds are giving continuous choices - by moving the destination around I'm sticking to the strategic choice up front, though I nearly wobbled this morning when I had to force the destination so far from Auckland. It's back there now :-)

Dave

Post by Armchairsailor | 2015-03-29 | 22:57:48

I noticed a deviation of the calculated twa by zezo compared to the calculated twa by the virtual regatta dashboard. I gues this relates to the 5 degrees increment you talk about.
Currently I am at a point where the wind direction is 279 degrees, The advised course is 52 degrees. If I calculate the TWA from these two figures it is 133 degrees. The advice mentiones 130 degrees. THe game console displays 133 degrees.
I wanted to say that your calculation is incorrect. But reading this explanation, it may make sense. ... but I do not know...

Post by lotsemann | 2015-03-30 | 01:30:12

The answer may lie in the red line linking the two points.

If you look at it, you sometimes will see it slighty changing direction -- 5 degrees, to be more precise.

It means that the TWA changes during the travel.

In your case, it probably means that the initial TWA was 130 degrees and the final TWA was 135 degrees.