Multilateration (MLAT) now available on PiAware!

We don’t include MLAT on the web in the US yet – our FAA data is currently delayed 5 minutes, so MLAT would always beat the FAA data. We’re switching to realtime data shortly and then we’ll bring in MLAT.

Hi,

For MLAT tracking, is the altitude displayed pulled directly from the Mode-S transponder or is it also computed based on multiple feeders like the location is?

I’m in a place where the majority of flights I care about don’t have ADS-B. MLAT flight paths jump around a lot, but it’s the altitude I’m most interested in, so wondering if I can put more confidence in that vs. the displayed path.

Thanks,

David

It is directly from the aircraft, not derived.

hi all,
i was running piaware 2.1.2 and had blue mlat aircraft showing on my display, I manually upgraded to 2.1.5, which went fine but no mlat blue aircraft showing post upgrade.
I view the output of dump1090 by using planefinder client localhost:30053 and here is where i used to be able to viw the blue mlat aircraft.
I have dump1090 malcom robb which i have found to be the most reliable.
Any ideas ?

Thanks in advance.

All altitudes are sent via aircraft, whether mode C/S/ ES/UAT(ADSB).
Mode C send pressure altitude(29.92" or 101.3mb. The ground stations correct this). Not 100% sure about S/ES. I have seen ES messages that state it is pressure or geodetic (GNSS) altitudes.

It is one of the limitations of radar(can’t tell altitude well) and why they added sending pressure altitude to mode A to get Mode C.

See more here
en.wikipedia.org/wiki/Aviation_ … tion_modes
en.wikipedia.org/wiki/Automatic … 81090ES.29
I watch some good, if self promoting, videos on ads-b yesterday. search ads-b university on youtube.com

Have a look here:
discussions.flightaware.com/ads … 36047.html
(The default port for multilateration results has changed.)

You probably have to make some port adjustments either to your dump1090 or the piaware mlat client.

mgunther , Now Restored to normal operation ,Many Thanks indeed for your help.

Regular Mode S altitudes are the same as mode C, the pressure altitude.

The primary altitude in ADS-B / ES is usually pressure altitude, but it also transmits the difference between the pressure altitude and GNSS height-above-ellipsoid in a separate field. (If pressure altitude is unavailable for some reason, HAE may be sent directly, but that is uncommon)

The pressure altitude is one of the inputs to the multilateration solver and it is heavily biased to produce a result that is close to the transmitted altitude. If mlat does not have a pressure altitude, though (e.g. the transponder is not being interrogated by a SSR or we’re not hearing the replies) then it will try to solve for the altitude directly. The results are not very reliable in that case (the altitude solutions are very sensitive to small errors because the receivers and the aircraft are roughly in the same geometric plane)

I had forgotten that we fly by pressure altitude. It makes sense that it is what the transponder reports.
We just change to 29.92/1013 when we get to the flight levels (around class A airspace in the US and Australia) so we don’t need to change it until we descend. Otherwise a fast aircraft would be changing it too often.

Hello,

looks like mlat data is getting worse. In the beginning I really had nice stratotanker flying ovals above my head but now never more. At the moment I have 129 nearby receivers.
Is there a measurement of the mlat quality?

Also other military aircraft looks bad.

Anyone have an idea?

Ludger

I’m trying to upgrade my PiAware from version 1.20 to the latest one so I could do MLAT. However, it doesn’t work for me.
Here is part of the upgrade and outcome.

pi@atc ~ $ sudo dpkg -i piaware_2.1-5_armhf.deb
(Reading database … 77808 files and directories currently installed.)
Preparing to replace piaware 1.20-1 (using piaware_2.1-5_armhf.deb) …
Unpacking replacement piaware …
insserv: warning: script ‘mathkernel’ missing LSB tags and overrides
Setting up piaware (2.1-5) …
Installing new version of config file /etc/init.d/piaware …
insserv: warning: script ‘mathkernel’ missing LSB tags and overrides
Processing triggers for man-db …
pi@atc ~ $ sudo apt-get install -fy
Reading package lists… Done
Building dependency tree
Reading state information… Done
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

What can I do to upgrade it to the latest version?

Thanks,
Rafal

That install looks fine. What isn’t working?

This is the final message. And on My-ADSB FA page it shows that I’m using v.1.20

Try or uninstall 1.2 then install 2.1.x.
Maybe also try
sudo apt-get update
sudo apt-get upgrade
And a reboot.

Have you restarted piaware after upgrading it? It doesn’t auto-restart on package install (because usually the package install is driven by piaware itself)

DOH!

Thanks guys! Didn’t even think about restarting my Pi :slight_smile:

Feeder Type: PiAware (Debian Package Add-on) 2.1-5
Multilateration (MLAT): Supported / Enabled

Everything is working now :slight_smile:

You may want to take another look.
It looks like mlat stopped after the reboot.
It says enabled but no neighboring receivers. Have you set the antenna location on the piaware website?

Check out this thread. It looks similar to your issue.
post189631.html?hilit=piaware%20port#p189631

Now I’m seeing this message:

This feeder is not being used for multilateration because its timing information appears to be unreliable. This can be caused by the site location being incorrect, or because your Pi is running out of free CPU.

What is timing information? Location is correct, CPU is running high, but not at 100%.

dump1090 uses Mode S messages to get timing information. It uses this to triangulate positions of Mode S aircraft.
If the information is not accurate or reliable, it cannot be used.
Do you have anything else running on the RPI? Is it a version one or two?

My RPI is version two. The only other thing that is running on my Pi is PF feed.

3655 pi 20 0 15788 6060 908 R 34.7 1.4 35:16.54 dump1090
3665 pi 20 0 75776 32m 5424 S 33.7 7.3 34:06.73 node
2132 root 20 0 11232 6812 2476 S 21.3 1.5 285:17.04 fa-mlat-client
3659 root 20 0 2352 708 596 S 2.9 0.2 3:01.98 nc
2025 root 20 0 17348 6484 3004 S 2.2 1.4 27:27.47 piaware
3660 root 20 0 2404 808 672 S 1.3 0.2 1:41.75 nc

FA MLAT client runs around 20% of the CPU