My understanding of the Flarm is that its primary objective is not to create an
overview of nearby traffic (which we do using different kinds of traffic
displays) but to analyze this traffic for possible threats and issue alerts if
such is found.
Having used it for some years now, I found that the LED based primary or
auxiliary Flarm display is pretty good at it. Also, the Flarm people have benn
putting some effort in flight path prediction and filtering. Gliders in the
same circle will be displayed but not cause an alert as long as they are in a
steady relative position more than about 60° before or behind you. Gliders
flying in parallel will also be displayed, but only cause an alert if the
relative speed increases or distance decreases so a collision is being
predicted. All this works pretty well.
Given this, seveal gliders flying nearby under a cloud street will see a LED in
the direction of AT LEAST ONE other glider, maybe there's more then one 'behind
that LED' if we look outside. It is simply a matter of resolution, if there's
only so many LEDs.
Now, with a traffic display overlaid on a moving map, I found that this does
not improve much. I will usually have my map zoomed so that I get a good
overview over the next relevant part of route planned, and that makes it
impractical for display of nearby traffic. Nearby traffic will only be shown as
a mess of overlapping icons buzzing closely around my own position.
For this reason, I think that using an independent display (like Butterfly
display) is recommendable for nearby traffic awareness and collision warning,
while for tactical considerations, it is desirable to display traffic on the
map. It is, in my experience, not a good idea to combine collision warning and
the map, as long as the zoom applies to both.
This said, It looks like XCSoar should focus on the tactical part when
displaying traffic in the map and keep distant Flarm traffic readable by
applying filtering and suitable timeouts. Flarm targets thermaling tend to pop
on and off in the fequency of their circle, so that might be a good timeout to
start with. In addition to a timeout, it could make sense to fade the icons of
weak flarm targets out over the timeout period in say eight or sixteen levels
of grey, one per second. That would stop them flickering about and give an
intuitive impression of the quality and reliabilty of their signal.
A dedicated display of nearby traffic (integrated, such as Flarm radar) is a
different story and must not use the same filtering. It needs to be faster,
zoomed closer, display only an area relevant for collision avoidance, and issue
very clear warnings. These may even cover the map, as it is not the right time
to fiddle with the map while a collision alert is going off, anyway. Using
sorts of filtering here might also be useful to cover traffic with bad Flarm
signal, but it must be made very clear to the pilot when a flarm target is not
'fresh', e.g. by fading or changing its colour. Maybe, just changing the icon
or extrapolating the position of the target is not enough, as it still creates
the impression of a certain relative position: It could make sense, to create a
growing circle around the latest fix, indicating it's possible positions after
the loss of the signal, and that the position is unsharp. This would probably
look like throwing stones in a pond, with a circle emanating from the last fix,
growing while fading. Still, it would at least provide a means to tell the
pilot 'there is something out there, somewhere', watch out.
Besides that, Flarm cannot replace looking out of your cockpit!
Viele Grüße
Martin Kopplow
---
Am 14.09.2012 um 07:34 schrieb SoarTronic team <[email protected]>:
> Implementing this somehow will improve safety. There are so many XCSoar/FLARM
> users now, that someone will avoid midair because of improved situation
> awareness if this is correctly implemented.
>
> I agree with having indication, if someone is flying same direction with you,
> near to you in blind spot, and he keeps disappearing from your FLARM. It is
> potentially dangerous situation. If this other ship has only LED based FLARM
> display, and there are several gliders nearby, he will not be able to notice
> the situation at all ! !
>
> FLARM is designed to alert you of other gliders in front of you, closing. If
> you fly high speed under cloud-street, FLARM is perfect (we do not have
> mountains here, so no experience of that).
>
> 2012/9/14 BRIAN CASE <[email protected]>
> Sorry I haven't been fully following this discussion so ignore if it doesn't
> apply.
>
>
> But if you don't fully like the idea below, how about changing the color of
> the of the target to indicate that it is an old target. I.E> Green if updated
> in the past two seconds. Yellow if more than 2.
>
> Brian
>
>
> Date: Thu, 13 Sep 2012 16:32:01 -0700
> From: [email protected]
> To: [email protected]; [email protected]
> CC: [email protected]
>
> Subject: Re: [Xcsoar-user] Flarm radar
>
> Mystery solved. Marc from Butterfly just responded to my question on RAS:
>
> > 8 - Does butterfly implement some kind of filtering which prevents targets
> > from disappearing momentarily due to loss of signal? This seem the case
> > when comparing to the flarm radar in XCSoar for example.
> Yes, we keep a target active for some seconds ( eight seconds) after losing
> reception (ADS-B and FLARM only).
>
> I recommend doing the exact same thing, to be consistent. I know some pilots
> disagree, but the only reason to disagree is if you plan to use XCSoar as
> your main collision alert system which is not recommended. The implementation
> in XCSoar is mostly for situational awareness, and as such, implementing the
> eight second delay will be beneficial. Also I trust the Powerflarm and
> butterfly folks that they did their analysis to come up with this filtering.
>
> Ramy
>
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