Help us with this petition for security on anti-collision systems

On Thu, 28 May 2015 13:58:39 +0000, Tim Newport-Peace wrote:

Firstly, the Easter Egg was built into the previous version of FLARM
firmware long before OGN can into being. OGN was not the cause. As I
understand it the Easter Egg was to ensure that users were on reasonably
up-to-date Firmware.

By Easter Egg, do you mean the protocol expiry date? If so its not what I
was talking about and I don't have a problem with it: given that FLARM
was designed for small, low-powered hardware, syncing protocol version
that way makes a helluva lot more sense that having to maintain backward
compatibility over the last 'n' protocol versions just because some lazy
git can't be bothered to keep his software up to date.

Secondly, any transmissions received by an OGN Receiver that have the
Do-Not-Track bit set are discarded at the receiver. There are never sent
to the Server.

Not necessarily: you can't guarantee anything like that if the receiver
is the result of a third party reverse engineering project, which is what
I've always heard about the RPi-hosted FLARM receiver units. If the
software author decides he wants to see everybody and ignores that bit
then pop goes your invisibility cloak.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

oh com'on, at the beginning of this thread I stated I did not sign the
petition. There is no deliberate action of any kind.
Simply you keep calling prediction what is really a projection.
If you are turning, it projects accordingly . It doesnt predict you are
turning.
"prediction" is a marketing word here. There is no computational power to
predict anything, inside the flarm.
But let it go, it does work, this is out of any question. We have been using
it since 2005.


"Andy Blackburn" wrote in message
...

On Thursday, May 28, 2015 at 2:16:55 PM UTC-7, Tango Eight wrote:
On Thursday, May 28, 2015 at 4:00:06 PM UTC-4, Buddy Bob wrote:
At 18:35 28 May 2015, pcool wrote:
Two flarm equipped gliders fly parallel to one another at 80 kts with 300'
separation and -- as long as the flight paths are not convergent -- flarm
gives no alarm. If the paths become convergent, alarms result very
quickly. As soon as the paths become parallel or divergent, the alarms
cease. The same two gliders now fly a head on approach, again at 80 kts.
Flarm gives a warning at significant range... over a mile... and the
warning ceases almost immediately when one glider changes his track. From
this I believe it should be clear to anyone that the way flarm works is
most likely just how they've said it works: by estimating what airspace
any given glider is capable of occupying in the next +/-30 seconds and
looking for potential conflicts.

-Evan Ludeman / T8

Yes. I'm surprised this is even coming up, except as a deliberate effort to
obfuscate important differences between the various technologies and why
they may not be compatible.

Anyone with a rudimentary knowledge of aircraft dynamics and even a single
day's flying with FLARM has to conclude that it is making path-dependent
collision prediction estimates. You have to fly in a few thermals to pick up
that the path prediction is curved when you are turning.

Flarm engineers have told me explicitly that the prediction is done on the
transmit side and I can see why this would work better for the reasons
previously raised. The specification may or may not need to specify this as
a communications protocol generally needn't include a specification of the
data payload or the algorithm to create or interpret it.

9B

sorry andy. I wish we lived closely, to have a great discussion about this
with a beer.


"Andy Blackburn" wrote in message
...

On Thursday, May 28, 2015 at 11:41:49 AM UTC-7, pcool wrote:
When you say "straw manning" you are talking about yourself, right?

Are we in 4th grade?

I was referring mostly to Lucas' misinformed and obfuscating rant, but also
to your inaccurate comments minimizing the difference between traffic
advisory and path-dependent collision warning. It is quite a big difference.

9B

I'll buy the beer.

Prediction, projection, position, protection. I'm not very clear on the finer points of my mother language apparently. ;-)

Here's how I look at it. FLARM calculates a projected flight path with a probabilistic "error radius" determined based on flight parameters to estimate a likely future position (assuming no change in control inputs) and then maps these paths to estimate likely conflicts and warns if it finds one. I consider that warning a prediction - if nothing changes the two aircraft will likely collide. Sure, it's an estimate but I still consider that more of a prediction than just putting airplane-shaped dots on a display and telling the pilot "you figure it out". I'd rather have a microprocessor and an algorithm than burying my head in a traffic display. I'd call that warning a prediction but maybe I'm being sloppy with the definitions.

The point is - FLARM will give you a warning only for pretty real threats. A traffic advisory system can only annoy you with constant warnings of aircraft in the vicinity whether they are a threat or not or leave it to you to find threats.by staring at a display. You need to project a flight path with some precision to strike a balance between too may false positives and leaving too many possible threats suppressed until too late. Given how we fly I think FLARM does quite well. It's also why ADS-B will struggle to operate as a collision warning system for gliders - even if someone tries to plaster a collision projection algorithm on top of some Garmin ADS-B unit. PowerFLARM throws out the ADS-B information if it detects a target with both FLARM and ADS-B Out.

9B

Now I understand what you meant with prediction, not referring to the
position!
yes I agree on this definition, from this point of view.
I look at it exactly as you do.

"Andy Blackburn" wrote in message
...

I'll buy the beer.

Prediction, projection, position, protection. I'm not very clear on the
finer points of my mother language apparently. ;-)

Here's how I look at it. FLARM calculates a projected flight path with a
probabilistic "error radius" determined based on flight parameters to
estimate a likely future position (assuming no change in control inputs) and
then maps these paths to estimate likely conflicts and warns if it finds
one. I consider that warning a prediction - if nothing changes the two
aircraft will likely collide. Sure, it's an estimate but I still consider
that more of a prediction than just putting airplane-shaped dots on a
display and telling the pilot "you figure it out". I'd rather have a
microprocessor and an algorithm than burying my head in a traffic display.
I'd call that warning a prediction but maybe I'm being sloppy with the
definitions.

The point is - FLARM will give you a warning only for pretty real threats. A
traffic advisory system can only annoy you with constant warnings of
aircraft in the vicinity whether they are a threat or not or leave it to you
to find threats.by staring at a display. You need to project a flight path
with some precision to strike a balance between too may false positives and
leaving too many possible threats suppressed until too late. Given how we
fly I think FLARM does quite well. It's also why ADS-B will struggle to
operate as a collision warning system for gliders - even if someone tries to
plaster a collision projection algorithm on top of some Garmin ADS-B unit.
PowerFLARM throws out the ADS-B information if it detects a target with both
FLARM and ADS-B Out.

9B

At 22:44 28 May 2015, Martin Gregorie wrote:
On Thu, 28 May 2015 13:58:39 +0000, Tim Newport-Peace wrote:

Firstly, the Easter Egg was built into the previous version of FLARM
firmware long before OGN can into being. OGN was not the cause. As I
understand it the Easter Egg was to ensure that users were on
reasonably
up-to-date Firmware.

By Easter Egg, do you mean the protocol expiry date? If so its not what I

was talking about and I don't have a problem with it: given that FLARM
was designed for small, low-powered hardware, syncing protocol version
that way makes a helluva lot more sense that having to maintain backward
compatibility over the last 'n' protocol versions just because some lazy
git can't be bothered to keep his software up to date.

Secondly, any transmissions received by an OGN Receiver that have the
Do-Not-Track bit set are discarded at the receiver. There are never
sent
to the Server.

Not necessarily: you can't guarantee anything like that if the receiver
is the result of a third party reverse engineering project, which is what

I've always heard about the RPi-hosted FLARM receiver units. If the
software author decides he wants to see everybody and ignores that bit
then pop goes your invisibility cloak.

In which case it is not an OGN receiver any longer.

"Don’t believe anything you read on the net. Except this.
Well, including this, I suppose."

DOUGLAS ADAMS (1952-2001)

On Wednesday, May 27, 2015 at 12:45:08 PM UTC+2, Kevin Neave wrote:
Since you ask...

The first hit from Google for "dsx systems t-advisor" is

http://frank.schellenberg.nl/wp-cont...r_07_12_19.pdf

This states..

"The Traffic Advisor, notifies the pilot the presence of all planes that
enter within the radio operating range (that for the T-Advisor is up to 7
km)"

I may be dim but I read that as "T-Advisor tells you 'that there are lots
of gliders flying within 7 km' ".

So I'll rephrase that.

It *would* tell me that there are lots of planes flying within 7km of me if
they were fitted with DSX.

The aircraft I'm interested in are the ones that are that are converging
with me. Flarm warns me of these as long as they are also Flarm equipped
Flarm is intended as an aid to lookout, generally I've seen most contacts
by the time Flarm generates a warning, occasionally I get a wake up call.
Flarm reminds me that my lookout is not as good as it could be.
(Of course I have no idea how many I'm missing and Flarm isn't picking up)

I don't see what T-Advisor would give me

A large number of the gliders flying XC in the UK (possibly a majority by
now) are using Flarm. I don't know of ANY using DSX.

So I repeat the question, how many gliders in Europe are using DSX?
Or more specifically how many in the UK are using DSX?

KN



At 23:44 26 May 2015, Lucas wrote:
Kevin Neave, can you show in which website you read that the T-Advisor
tells you "that there are lots of gliders flying within 7 km" ?

Kevin, I understand that the sentence can be read in a way different from what was intended: the T-Advisor notifies the pilot of the NEW presence of a glider within range. It blimps once, to tell the pilot that there is a glider there, and will not continue indicating it to the pilot (how could it indicate continuously all gliders in range, on a led display ? Obviously this is impossible, beside useless).

Your comment derives from the fact that you have not had the chance of flying with a T-Advisor, otherwise you would have noticed how it works. Way differently from what you think. But you have forgotten to read the rest of the manual, where it is clearly specified that the system warns the pilot only about gliders that are going to possibly collide.

All pilots with T-Advisor, that has been developed with the input of all of them, are extremely happy to be notified when a glider enters the operating range of the system: it is very helpful to spot another glider at a quite long distance, not mainly for collision avoidance but for information. Also in competitions.

Therefore, the T-Advisor doesn't keep beeping for *any* aircraft in range, buto only for those that are close to possibly collide, warning the pilot with different levels of beeps and led flashes depending on the severity of the situation. This doesn't mean it decides which plane is more dangerous: it tells you what planes are going to hit you based on the approaching speed/distance = time to impact. The warnings are prioritized according the time to impact.
The pilot decides, ultimately.
What it doesn't is to decide which threat to display and which not, based on a "prediction", that, I reiterate, is impossible for a glider not flying with a regular trajectory (straight of stable rate of turn - it's enough to look at the glider traces of any flight to understand this).

I think that your worries are

On Wednesday, May 27, 2015 at 10:35:46 PM UTC+2, Andy Blackburn wrote:
On Tuesday, May 26, 2015 at 4:44:07 PM UTC-7, Lucas wrote:
The T-Advisor AND Flarm are NOT anticollision system.
Anticollision systems are those who tell the pilot what to do (like TCAS), in case of emergency. Neither system does this.
BOTH systems are NOT anticollision systems.

This is a bit of a hair-splitting argument, but to be clear - there a 1) Traffic display systems (show traffic within a detection volume, but provide no alerts), 2) Traffic advisory systems (alert to new traffic entering a detection volume - like PCAS), 3) Collision detection systems (calculate and warn of other aircraft on a probable collision path - like FLARM), 4) Anti-collision systems (advise pilots on action to avoid a collision), 5) Automated anti-collision systems (autonomously take action to avoid collisions - I'm not aware of any of these - outside of military terrain-following autopilots).

Usefulness goes up as you move up the hierarchy. IMO FLARM, being higher that other systems is more useful.


Cleared this, those who talk about the "predictive algorithm", can please explain:

1) how it works, since they must know how it works, to be in the position of saying that it works or it doesn't

2) how they know that such an algorithm has been implemented into a Flarm system: what proof do they have of this ?

Really? That's a serious question? Well, it warns me of converging traffic and when I look, there is in fact converging traffic in the direction indicated. There is no traffic converging on me for which I get no warning and warnings for traffic that is not a series factor is almost nonexistent.


3) if they have ever seen the trace of at least 10 glider flights in different conditions (competition, cross country, around-the-airfield, ridge soaring,....); whoever has seen some, not many, traces of flights, without the need to be a glider pilot, can understand that a prediction of the position of a glider in a future time beyond a fistful of seconds is impossible, exactly IMPOSSIBLE, since not even its pilot knows it, apart from some cases, like straight flying and constant turn rate thermaling. A glider pilot knows that he will be changing the trajectory of the glider to search for the best netto value, which depends on the micro air movements, which are unknown to the pilot in terms of exact location. Is there a machine capable of predicting these locations ? And even if there was, is there a machine capable of predicting what a glider pilot will do in the next 30-60-80 seconds ? Because this is what the rumored (never verified) "prediction algorithm" does. This is spectacular indeed !

Impossible? As a control-systems engineer I can tell you for a fact that a 1 second sample rate is perfectly adequate for this purpose and you only need 2-3 good data points for each aircraft to make a decent prediction. Even with dropped packets this is a reasonable task. Glider flight dynamics are not so abrupt as to make this an impossible task and pilots are not generally making so many aggressive control inputs as to flail the system. FLARM uses a probabilistic approach base on total energy to err on the side of possible control inputs that handles most situations well.


4) even if they found a system to predict the position of the glider with a certain probability, would they trust as optimal a system that has (obviously) a probability to fail the prediction and miss a danger of collision ? Even if the probability was low (all but sure, since never demonstrated with objective tests and calculated data), 2, 3, 10 collisions (and deads) out of XX'XXX flights are too much. In aeronautics, this approach is wrong: this is not the way we work in professional aeronautics, that has taken us where we are in aviation

We don't need optimal, we need better than human perception and FLARM does that very well indeed.


9B

Andy, the T-Advisor is a
3) Collision detection system
Obviously there are different ways to detect a possible collision: to be "extreme", just to make the difference evident illustrating the two extreme positions, you can predict a collision based on approach speeds (very objective and 100% sure data) or using a crystal ball (0% objective and totally unsure data). There are ways in between, obviously.
If you possibly had the responsibility of a life, I am sure you would not go for a "probabilistic" approach, but you would base the functioning of the system only on 100% sure data.
And for a collision, the only sure data are the relative approach speeds and distance, hence time to impact. The rest are speculations about what the pilot will or will not do: you can be in a trajectory considered safe for a predictive system and suddently feel the right wing raising and deciding to turn right, where, by chance, there is another plane in your blind spot. No system can predict this.

When you write:
"it warns me of converging traffic and when I look, there is in fact converging traffic in the direction indicated. There is no traffic converging on me for which I get no warning and warnings for traffic that is not a series factor is almost nonexistent."
That is exactly the same output you get from a T-Advisor, based on the approach speed and distance of the surrounding planes.
This should show you that what you wrote doesn't demonstrate that any "prediction algorithm" is in place.
So you don't know what is implemented in Flarm because, on the contrary of the systems developed with an aeronautical procedure, it's not verified by anyone.

"Prediction": you are a control system engineer, therefore you work with deterministic systems. The glider pilot, whose actions depend on atmospheric conditions unknown a priori (i.e. vertical gusts/thermals), is not a deterministic system.
I agree with you that it is possible to say with an approximate precision where a glider will be in 2-3-4 seconds, because it's dynamic is slow compared to this time length and, in few seconds, the most abrupt control inputs from the pilot will not deviate it a lot from the existing trajectory. But it is clear to any glider pilot or person who sees a flight trace that affirming that a system can "predict" where the glider will be in 20-40 seconds anytime, is like saying that it has a real crystal ball.
It looks like discussing of the obvious: take a flight trace and place yourself in any position along it and then say if you could have told where the glider would be after 20-40 seconds. Leaving aside the straight glides and regular thermals.
This is indisputable, I think.

We don't need optimal, we need better than human perception and FLARM does that very well indeed.
If you had to design a system to save the life of two persons, I am sure you would not take a probabilistic approach, but you would take a path based on 100% sure data. Since these are available (approach speed/distance = time to impact, although calibrated with some other parameters like relative altitude and others).
All system are improving human perception: this is not the point.
The point is which approach is safer, surer for avoiding a collision. An engineering discussion.

On Friday, May 29, 2015 at 10:41:02 AM UTC+2, Lucas wrote:
On Wednesday, May 27, 2015 at 12:45:08 PM UTC+2, Kevin Neave wrote:
Since you ask...

The first hit from Google for "dsx systems t-advisor" is

http://frank.schellenberg.nl/wp-cont...r_07_12_19.pdf

This states..

"The Traffic Advisor, notifies the pilot the presence of all planes that
enter within the radio operating range (that for the T-Advisor is up to 7
km)"

I may be dim but I read that as "T-Advisor tells you 'that there are lots
of gliders flying within 7 km' ".

So I'll rephrase that.

It *would* tell me that there are lots of planes flying within 7km of me if
they were fitted with DSX.

The aircraft I'm interested in are the ones that are that are converging
with me. Flarm warns me of these as long as they are also Flarm equipped
Flarm is intended as an aid to lookout, generally I've seen most contacts
by the time Flarm generates a warning, occasionally I get a wake up call.
Flarm reminds me that my lookout is not as good as it could be.
(Of course I have no idea how many I'm missing and Flarm isn't picking up)

I don't see what T-Advisor would give me

A large number of the gliders flying XC in the UK (possibly a majority by
now) are using Flarm. I don't know of ANY using DSX.

So I repeat the question, how many gliders in Europe are using DSX?
Or more specifically how many in the UK are using DSX?

KN



At 23:44 26 May 2015, Lucas wrote:
Kevin Neave, can you show in which website you read that the T-Advisor
tells you "that there are lots of gliders flying within 7 km" ?

Kevin, I understand that the sentence can be read in a way different from what was intended: the T-Advisor notifies the pilot of the NEW presence of a glider within range. It blimps once, to tell the pilot that there is a glider there, and will not continue indicating it to the pilot (how could it indicate continuously all gliders in range, on a led display ? Obviously this is impossible, beside useless).

Your comment derives from the fact that you have not had the chance of flying with a T-Advisor, otherwise you would have noticed how it works. Way differently from what you think. But you have forgotten to read the rest of the manual, where it is clearly specified that the system warns the pilot only about gliders that are going to possibly collide.

All pilots with T-Advisor, that has been developed with the input of all of them, are extremely happy to be notified when a glider enters the operating range of the system: it is very helpful to spot another glider at a quite long distance, not mainly for collision avoidance but for information. Also in competitions.

Therefore, the T-Advisor doesn't keep beeping for *any* aircraft in range, buto only for those that are close to possibly collide, warning the pilot with different levels of beeps and led flashes depending on the severity of the situation. This doesn't mean it decides which plane is more dangerous: it tells you what planes are going to hit you based on the approaching speed/distance = time to impact. The warnings are prioritized according the time to impact.
The pilot decides, ultimately.
What it doesn't is to decide which threat to display and which not, based on a "prediction", that, I reiterate, is impossible for a glider not flying with a regular trajectory (straight of stable rate of turn - it's enough to look at the glider traces of any flight to understand this).


..... I think that your worries are

Sorry: it was posted inadvertently, before completion:
I think that what worried you is clear now.
Again: pity you hadn't got the chance of flying with a T-Advisor.
Most T-Advisor pilots have been reporting their satisfaction about how the system warns them about surrounding traffic and risk of collisions.
None of them has ever said that it's annoying in thermals and has to turn down the volume. And this is another difference to the other system.
All of them reported that the function that informs them about the position of another plane entering into the range is very useful.
Many T-Advisor pilots are ex-Flarm pilots.

We wish to thank everybody. We have some 900 pilots (and are growing) that think that the protocol should be free and then everybody is free to buy the system he prefers!

No monopoly, especially on security. IGC should agree with this.
THANKS AGAIN