yea, this option would be great. Some people in my glider club are going to change the software and start working with xcsoar. The only disagvantage right now is, that this option is missing. So some people will not change before this option is available.

Any chance to implement this in 6.5?

See also #2299.

Is there anybody who plans to implement this?
I had some flights this year on which such a feature would have helped a lot.

Can this be moved out from wishlist to 6.5? I having few flights every year in which I wish such a feature was available.

if anyone finds out how SeeYou? for example is calculating these things we can implement it. how for example does SeeYou? know when you have turned? how does this feature really work? as soon as someone can tell us very specifically what is needed we can implement it. saying we want a "FAI triangle assistant" is not specific enough...

I don't know how SeeYou? calculates it but here is my guess:
The purpose of this feature is to tell you the area you can turn for a valid FAI triangle assuming you already have 2 turn points, so basically it is looking for all possible FAI triangles that can be done based on continuously optimizing the first 2 turn points. The end result is an area highlighted on the map for optimum FAI triangle. This is very useful for OLC triangles since it guides you to the direction and distance you should go for your last turn point. This may be documented in SYM manual but I didn't confirm that yet.

I just noticed that the relevant page in the SYM manual which explains how it works was already provided in the duplicate ticket mentioned above (#2299).

yea, thats right. There also needs to be the option to switch the direction of the possible fai turning area. Based on the first leg it could be right or left of the track. It should also be able to handle starts on a triangle leg. In this case the second leg is the base leg for optimization and the direction is towards the start point. Additionally there is a different percentage allowed for the shortest leg. Usually it is 28% below and 25% above 500km according to the German DMST rules. In seeyou this can be adjusted in the configuration page.

okay so basically that means: find the two points in the previous track that have the largest distance between them, use that as the given leg and display the two FAI areas related to that leg, correct?

That would be one case. Another one would be when you are already on the second leg right in front of the area where you have to turn before you fly home. At that point the fai turning area might just be a few km ahaed. With application of only the first method, the fai turning area would be shown to be far away, either on the left or on the right of the line between the start point and the current location. Probably there needs to be an evaluation if the second case might be true.

how does SeeYou? distinguish between those two cases? does it actually do that? what is your opinion on how XCSoar should do it?

if we use my naive implementation and your scenario the FAI areas will indeed be shown on both sides of the second leg. I'm not sure though if this is really a problem, because you can just fly in the same direction until one FAI area is above your start point and then you know that you have a valid triangle.

Turbo, I am hoping someone, perhaps Chris, who have experience with this feature can elaborate more. I never flew with SYM myself, but in few cases, at the end of the day, two of my buddies who fly with SYM turned out a beautiful 1000km FAI triangle, while my flight, although longer overall, ended up around 950km FAI triangle since they knew where to turn while I didn't.

Thanks for asking.
Here is my suggestion:
Basically there are two functions, the first one finds valid base legs, the second shows the fai areas.

1. fct: findBaseLegs:

Basically there are 3 base legs. The first one is the one made of the longest distance found on the track. The second and third one are found by looking for the longest distance over one turnpoint.

2. fct: show fai areas:

below 500km triangle distance the shortest leg is 28%. 500km and above: there the minima for shortest leg is 25% and the maxima for the longest leg is 45%. In most cases the area for below 500km and above 500km touch each other, but sometimes they do not. Then there are two fai areas.
In SY and StrePla? it is possible to set the fai requirements manually (all 4 parameter)

3. Filtering: Wenn applying this function for finding the base legs, then sometimes leg2 and leg3 might be nearly parallel to leg3 (longest leg found). In this case there is no need to show the fai areas for leg2 and leg3. This could be made by setting an requirement, e.g. don't show leg 2 and 3 if

leg2 + leg3 < 1.15 leg1.

4. How to display

Generally the are several options.
a) area is just shown for one base leg
b) areas for all base legs are shown at the same time
c) show left and right side fai area for a base leg
d) show just one side fai area

I would like to only see one area at a time, so its a) and d). Then there needs to be a possibility to switch between the areas (legs and directions). In SY this is called "rotate fai sector". This could be made by a button in the view menu and additionally by a shortcut.

Two more things...

It is very nice if one could fly towards a fai sector and zoom in on arrival. Then one can really be sure that one was inside of the sector. Its true that one could also fly until the start point / proposed triangle corner point is in the sector, but this requires a large scale of the map. It will be difficult to see when the triangle is large... e.g. 500km and more. The goal is to just get into the sector and fly home. This is only possible when we can zoom in and see our plane flying into the sector. SYM handles that the same way.

The algorithm described above also handles fai triangles with start on a leg.

could you explain the "findBaseLegs" in a bit more detail? not sure I understood that concept yet...

My approach would be to find the three longest legs of the flight. Therefore the function used for the OLC-Plus optimization (Analysis - Info - OLC-Plus) can be reused, just with less allowed waypoints.

1. Leg1 - the longest leg:

The function can be reused with zero allowed waypoints, resulting in the longest straight distance within the track.

2. Leg2 and leg3

The function can be reused with one allowed waypoint, which results in two legs, which are connected to each other be one waypoint. These legs are leg2 and leg3.*

This will result in 6 different areas, two for each leg. I guess that the one feasible for the pilot is one of the suggested areas. He now can select the one which fits best for him.

*filter to leg2 and leg3 can be applied, like suggested above. --> don't show fai areas for leg2 and leg3 when leg2 + leg3 < 1.15 leg1.

1db19f3a9882145eabaf1885dc5c5b54f5dd8b0b

See ​http://forum.xcsoar.org/viewtopic.php?f=12&t=794 for screenshots.

looks great, can't wait to try it myselt. good job!

Thanks, that was quick! looking forward to use it next summer at Ely.

Fai triangle display test

Hi, I tried it. The basic funktion works, but there are still some improvements possible.

1. I could not find a place where the difference of triangles below and above 500km could be set. On my map both are treated the same way. @Max, in you screenshot the difference is shown. What do I need to change to get the same?
2. Function seems to work up to the second leg. Now we can easily fly into the FAI triangle sector... but I would be great to have the possibility to do that with a third waypoint as well. This matters when the second leg is the longest and if one wants to fly a FAI triangle with start on a leg. The areas based on the second (here longest) leg should be shown as well. I attached a file. ​http://bugs.xcsoar.org/raw-attachment/ticket/1563/FAI_triangle_test.png ...here it would be nice to see the area south west of the target airport. Then one could extend the FAI triangle or make sure one got one finally for the case that one could not fly set the second waypoint into the fai area.
3. I also agree with ticket #2442 that line which show the distance would be nice. I'm not sure about showing only one FAI area and turn them around. This would be good (similar to seeyou), but I also like the idea of seeing all areas at the same time. Maybe one can make it that way that one could switch the areas and also switch between seeing all and only one at a time. So for the case that there are 6 areas, then one could switch between 7 options (6+all).
4. By the way, the triangle on the attached picture is supposed to be a fai triangle. According to the picture it is not... I'm not sure what went wrong (smallest leg is 28.1%).

Hi, as far as I know, the issues I posted 3 month ago are still open. I have tested the new 6.5 XCSoarTesting versions, and I could not find any changes compared to the time of my last post, please see above. Hence I opened the ticket again. E.g. the different settings for the FAI triangles for the >500km triangle are important. Thx.