Heading display of target aircraft in nav software

[Ian Melville]

Does anyone know how the heading of the other aircraft depicted in navigation software is derived? SkyDemon in particular. There is nothing in the messages sent to the nav software from PAW.

I had an RV on the same track as myself, but facing wrong way. I expected it to whip past me from the opposite direction, but it was 500' below me and overtaking. As it would, Vagabond v RV9 no contest :-)

[brinzlee]

I noticed that the other day on an ADSB target. The Aircraft symbol was tracking backwards, I was using a groundstation and again using SkyDemon but the PC version. I thought it was just a glitch or seeing things....These new breed of aircraft don't have reverse do they ?

[EricC]

I presume that the lat.long and speed info transmitted, will show the Track of the aircraft over the ground.
The Heading can only displayed if wind info is available and calculations are completed.
A stationary gps has no idea where north is.

[brinzlee]

When in ground mode....my notation always seems to point northerly....I understand what you're saying but all the other aircraft have never flown backwards.

[EricC]

Very interesting, using  xcsoar it shunts round all the time in ground mode.

[Admin]

Hi Ian,

The track is indeed provided as part of the message which goes to the NAV device.
What you describe reminds me of a posting I saw elsewhere, and I seem to recall it was a transponder fault.
I think it is even posted somewhere on this forum.
aha found it :-
http://forum.pilotaware.com/index.php/topic,286.msg3971.html#msg3971

Thx
Lee

[Admin]

Very interesting, using  xcsoar it shunts round all the time in ground mode.

Hi Eric,
yes very annoying, I have noticed this too.
So a little background, when the G/S is less than 5kn I always send the TRACK North message to the NAV
device - which describes what Brinz has seen, otherwise the data is just not reliable enough.

In the case of XCsoar - I think it is not using the TRACK information, I think it is calculating the TRACK itself
from the GPS supplied co-ordinates, and of course if you are stationary, there is going to be some tiny jitter
in your position, which is why I decide to ignore the GPS supplied TRACK at a speed of less than 5Kn as above.

Thx
Lee

[Ian Melville]

Hi Ian,

The track is indeed provided as part of the message which goes to the NAV device.
What you describe reminds me of a posting I saw elsewhere, and I seem to recall it was a transponder fault.
I think it is even posted somewhere on this forum.
aha found it :-
http://forum.pilotaware.com/index.php/topic,286.msg3971.html#msg3971

Thx
Lee

Thanks Lee, not sure if it was displaying the aircraft track north. Pity I was not recording the Sydemin screen. It was 180 degrees to my track so if I can find the time, I should be able to work out if that was the case.

you are right the heading should be in the message.

Most confess I was worried about a target hurtling at me, but could see nowt, coz the cheeky blighter was creaping up from below and behind. It was only when I made a deliberate heading change to see him, that I spotted him.

[exfirepro]

On the positive side Ian, you did get a warning which led you to find the inbound target - just not from the direction you expected.

Regards

Peter

[Admin]

Hi Ian

Most confess I was worried about a target hurtling at me, but could see nowt, coz the cheeky blighter was creaping up from below and behind. It was only when I made a deliberate heading change to see him, that I spotted him.

More Importantly, if you can work out his Reg from the saved track logs, you should probably see if you can contact him, because there is clearly an issue with his transponder.
"Mis-information is worse than no-information"

Thx
Lee

[Ian Melville]

I do know the reg as I have already looked it up on G-INFO to establish it was an RV9. In the logs his track and groundspeed are both zero. Some CAT also display zero in these fields, which I guess would force the image to display heading north?

I'll drop him a letter.

On the positive side Ian, you did get a warning which led you to find the inbound target - just not from the direction you expected.

I just wanted to understand where the issue was. To me it was very positive, as I was about to descend and re-join the circuit. The alert made me stay level until I spotted the other aircraft. Closest he got was 2km and 700' below. I suspect he would have had clear sight of me so would have moved away had I started a decent, but we will never know