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Transponder over network

OpenRadar is a standalone radar screen which connects to the FlightGear multiplayer servers. It is currently being developed.

Transponder over network

Postby F-JJTH » Sun Apr 28, 2013 8:42 pm

Hi all,

In real life the transponder is one of the most important instruments. It's a required instruments in most of our world because he is here to identify and locate aircraft for ATC controller.
Without transponder the real world airspace coudn't exist today.

This instruments is present in FlightGear but not usable because he is not implemented to work over network. FlightGear being a simulator I think it's important to implement this missing feature, that's why I've implemented it.

I've implemented mode A, C and S with following specification :

Mode A :
- Send only id-code (sqwak) ( read it over mp at : /ai/models/multiplayer[x]/instrumentation/transponder/id-code )
- Require a power supply /systems/electrical/outputs/transponder > 1.0
- Require /instrumentation/transponder/inputs/knob-mode > 0 ( 0=OFF, 1=SBY, 2=ON, 3=ALT, 4=TST)

Mode C :
- Send id-code (sqwak) /instrumentation/transponder/id-code
- Send altitude with 100ft precision /instrumentation/transponder/altitude ( read it over mp at : /ai/models/multiplayer[x]/instrumentation/transponder/altitude )
- Require a power supply /systems/electrical/outputs/transponder > 1.0
- Require /instrumentation/transponder/inputs/knob-mode > 0

Mode S :
- Send id-code (sqwak) /instrumentation/transponder/id-code
- Send altitude with 10ft precision /instrumentation/transponder/altitude
- Require a power supply /systems/electrical/outputs/transponder > 1.0
- Require /instrumentation/transponder/inputs/knob-mode > 0

The difference between C and S mode is only the altitude precision (100ft - 10ft) in real life S mode is able to transmit flight-number/callsign/immat but since we are already able to read callsign it's not necessary to add it into the transponder.

All changes are compatible with old FG versions. I've just added 2 properties over MP (id-code and altitude) so old FG versions are simply ignored these 2 news properties.
For those who are interested, here is the commit on my clone : https://gitorious.org/~f-jjth/fg/f-jjth ... 4b95086150

It require a modification in FGDATA here is the diff (easily doable by hand) :
Code: Select all
diff --git a/Aircraft/Generic/generic-instrumentation.xml b/Aircraft/Generic/generic-instrumentation.xml
index 6c8850c..69b9ad4 100644
--- a/Aircraft/Generic/generic-instrumentation.xml
+++ b/Aircraft/Generic/generic-instrumentation.xml
@@ -108,7 +108,7 @@ file, these values will be used (they are hardcoded).
   <transponder>
     <name>transponder</name>
     <number>0</number>
-    <mode-c-altitude>/instrumentation/encoder/mode-c-alt-ft</mode-c-altitude>
+    <mode>C</mode>
   </transponder>
 
   <turn-indicator>




For those who use a dedicated instrumentation.xml file you can define the transponder mode with the <mode> tags, like :
Code: Select all
<?xml version="1.0"?>
<PropertyList>
   <transponder>
      <name>transponder</name>
      <number>0</number>
      <mode>A</mode>
   </transponder>
</PropertyList>


Code: Select all
<?xml version="1.0"?>
<PropertyList>
   <transponder>
      <name>transponder</name>
      <number>0</number>
      <mode>C</mode>
   </transponder>
</PropertyList>


Code: Select all
<?xml version="1.0"?>
<PropertyList>
   <transponder>
      <name>transponder</name>
      <number>0</number>
      <mode>S</mode>
   </transponder>
</PropertyList>


For those who want implement their own transponder working over network, here is a demo with KT76A : http://clemaez.fr/flightgear/KT76A.tar.gz
With the XML file you will see which property needs to be modified, I plan to write a documentation when this feature will be accepted then commited in FG repo.


I hope this new feature will improves realism of FlightGear and ATC controller will be happy to work with it like it's done in real life.
I will create a merge request after first reactions from here, in order to see if this new feature is welcome or not by pilots/controllers.

Cheers,
Clément
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Re: Transponder over network

Postby Omega » Sun Apr 28, 2013 10:02 pm

This will require some kind of button probably implemented within OpenRadar that assigns squawk codes to targets. There are certain ranges (in numbers) for squawk codes depending on which airport you go. A good bet is that we can somehow load .pof files (which are used in vatsim clients to store squawk codes and frequencies) into OpenRadar.
If the aircraft is squawking as assigned, then altitude and speed will appear on the scope.

The aircraft-side of the transponder might be easy to implement, but squawks are not of any use until something happens with the ATC-side of things, which I don't think will be so easy to develop.

Nothing is impossible though, so I'll look forward to this.
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Re: Transponder over network

Postby F-JJTH » Mon Apr 29, 2013 6:35 pm

Hi Omega,

The aircraft-side is already implemented, it's exactly what my work done.
On the ATC-side it's not really difficult, ATC-side just need to ignore callsign information sent by FG because in real life the callsign of an aircraft is unknow until the pilot tell his callsign to the ATC controller. Once the ATC controller knows the callsign of the aircraft he assigns a sqwak code and make the association between callsign and sqwak code.
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Re: Transponder over network

Postby F-JJTH » Tue Apr 30, 2013 1:07 pm

Hi,

I've read more papers about transponder function and I plan to implement the "IDENT" function.
In real life, when the pilot press the "IDENT" button a special signal is sent to the ATC, in result, the ATC can see the aircraft highlighted on his screen.

Technically I plan to add a property ( /insturmentation/transponder/ident= TRUE/FALSE ) shared over network. So you just need to implement a listener to this property, if the property is TRUE = aircraft must be highlighted.
Let me know if you are interested about this and ready to implement.

Cheers,
Clément
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Re: Transponder over network

Postby Omega » Tue Apr 30, 2013 10:12 pm

Ident sounds good, what about squawk standby though, is that implemented? In squawk standby, the datatag should be blank and only the target appears.
Just so there won't be any misconceptions by the OpenRadar developers, squawk ident will make the data block flash for about 5 seconds. Not highlight.

I also wanted to add one more statement to the implementation of this in OpenRadar. I know this has been discussed before, but the best thing to have is radar hand offs so the identification of the aircraft can be handed off between each controller, so a new squawk won't have to be assigned every time.
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Re: Transponder over network

Postby F-JJTH » Wed May 01, 2013 8:14 am

Hi Omega,

Omega wrote in Tue Apr 30, 2013 10:12 pm:what about squawk standby though, is that implemented? In squawk standby, the datatag should be blank and only the target appears.


Do you have some reference about this ? I've read a lot of paper and never seen this. Here are my reference :
- Bendix King KT76C : http://www.neboservice.ru/docs/0897493001195543990.pdf page 46
Standby
- The unit is energized, but is inhibited from replying to any interrogation. “SBY” is annun-
ciated on the display in this mode. The altitude display is blank

- Garmin GTX330 : http://www.mstewart.net/Downloads/GTX330_IM.pdf page 34
Selects the standby mode. When in standby mode, the transponder does not reply
to any interrogations.

- Garmin GTX328 : http://www8.garmin.com/manuals/GTX328Tr ... sGuide.pdf page 4
Selects the standby mode. When in standby mode,
the transponder will not reply to any interrogations.

- Bendix King KT76A/KT78A : http://www.aea.net/TechPubs/BendixKing/ ... 78a_r7.pdf page 34
Any time that the function switch is in the "ON" or "ALT" position the transponder becomes an active part of the beacon system
Which means that in other mode, he is not "active".


Omega wrote in Tue Apr 30, 2013 10:12 pm:squawk ident will make the data block flash for about 5 seconds. Not highlight.

"Highlight" is maybe a wrong word definition, maybe you prefer "bring out" ? (Sorry, English is not my native language)
I invit you to read this topic : http://www.airliners.net/aviation-forum ... ain/69061/ As we can see, what happens on the ATC screen depends of the system used by the ATC. Feel you free to make your choice and implement the one you prefer ;)
Also, I think you can safely call the nearest airport tower and ask for a visit to the tower. I know it's possible to do at my local airport, if you are interested I can try to visit him and report you what I've seen on the ATC screen.

Cheers,
Clément
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Re: Transponder over network

Postby Omega » Wed May 01, 2013 10:15 pm

A radar has only the ability to calculate the aircraft's position, all the rest information is received by the aircraft's transponder. In most transponders, the first two modes are OFF and STBY. OFF obviously turns off the transponder, STBY turns on the transponder allowing the pilot to change squawk codes, but the transponder will not send any information until it is switched to mode C.
With the above statement, it is easy to make the conclusion that only the target of the aircraft (its position) will be visible on a scope.
Image

Now, if the aircraft is squawking mode C but a non-discrete code, then only the squawk code and altitude will be depicted.
Image

I do have to agree with you for how squawk ident is depicted. In most, if not all radar systems used in the US (STARS, ARTS and DSR to name a few) the tag will flash for a brief period of 5 seconds.
In TAATS, which is used in Australia, squawk ident will be depicted by a simple change of color in the target:
Image
Instead of the circle being light green, it has changed color to cyan.

What is a pity though, is that OpenRadar doesn't try to simulate any real-world radar system out there. So making such decisions is just based on opinions and not facts.

Although to conclude:

Squawk STBY: No information received, only target appears on the scope.
Mode A/TA: Used for identification -- Callsign and squawk code are depicted.
Mode C/TARA non-discrete: Callsign, squawk code and altitude are depicted.
Mode C/TARA: Callsign, altitude and groundspeed are depicted.
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Re: Transponder over network

Postby F-JJTH » Wed May 01, 2013 10:30 pm

Ah ! I didn't understood you spoke about radar capability. I was thinking about transponder system :wink:
Now the developper of OpenRadar has some work if he want :)

But my work is not yet merged in flightgear/fgdata for now...

Cheers,
Clément
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Re: Transponder over network

Postby Michat » Thu May 02, 2013 5:13 am

Using as a pilot with Vatsim client called FSINN.

In ground, Mode Stand By S (orange)

Just over RWY mode C (green)

Ident is not usually used. However I used it as a transition mode, so when I set to S or C, I see Ident for about 1-2 seconds before it takes mode. Kind of trick, helping the controller to see at first time who am I. Ident is represented with green font over a green square.

So, was clear that VATSIM's FSINN client is not all about realism. :lol:



Note: in my mockups show for OpenRadar. I though on that transponder topic. I did ASIC mode A, mode S, mode I, mode C.

I'm not a programmer, I can't change the world :mrgreen:

I'm agree that we could recreate a more realistic ATC client.
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Re: Transponder over network

Postby Secret_Hamster » Wed May 08, 2013 7:18 pm

I think the main reason for OpenRadar not using a proper radar system is the sheer point that there is no ability in the FGMS system at the moment implementing that. Currently each servers knows where all the clients are located (virtually) and then passes on the information to clients who are within 100nm of one another. Using this is a simple radar mechanism, currently there are no radar stations mapped into the system.

Now I suppose that could be implemented, but that is a massive ask of the OR developer to then go and map out all radar systems from around the world. If Wolfram is to do that, then what about radio systems. In essence this would see OpenRadar take over from FGMS in a number of ways. I mentioned this before, but FGMS and MP need an overhaul. Perhaps we should look at doing this work as an OR community as I don't see any of the current element of developers looking at this area, except maybe James, but from a slightly different view (ILS etc)
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Re: Transponder over network

Postby wagnerw » Fri May 10, 2013 7:44 pm

Hi,
Next step in development for me is to rework the internal construction of the data block in radar and the flight strips. After that, additional lines or situation adapted display are a lot easier to realize.

One of the next changes might be to add the processing of transmitted squawk codes and a first simple OR to OR coordination/communication. I hope that I can "deliver" in time with a general availability of transponders in the planes of FG.

Before we discuss the color of ident highlighting, we should think about, how we want the squawk assignment to be in OR. I have no clue how real ATCs do it. Omega proposed the Vatsim files. Do they have a matching license? Is there a public file server from where we can download them in the background?

And before that, we should think about the data in the radar contact data blocks in the radar map. Currently it is always the same. In future, we will have contacts with and without a transmitter in their airplane (Clement, I guess, we need another value in MP protocol to separate them? Because standby mode is not sending content at all?), contacts with squawk enabled or transmitter in Standby,, contacts with a more recent transmitter sending its altitude along with its id...
My thoughts to this:
  • is to use the existing scheme, as long as there is no transmitter built in.
  • If there is a transmitter in standby, we could show the place where it is, maybe with the grey callsign, to be able to address him.
  • Enabled Transmitter, callsign, current squawk, altitude if available, and speed
We must decide, if we want more reality or usability, in detail, if we omit altitudes, if they are not transmitted or not. And Omega, how comes the aircraft type into the game? Is it delivered with the flightplan? How does it work in real live? Flightplan filed under Callsign and Flightnumber => Contact identifies itself => ATC tells Contact Squawk code and assigns it to flightplan?

Do we really want to force everybody to file a flightplan, before he can fly at your airports? Or do we alternatively accept anything flightplan like be it per chat or voice. In the later more beginner friendly way, we could keep it more simple...

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Re: Transponder over network

Postby Johan G » Fri May 10, 2013 8:30 pm

I have recently tried to read in a bit on real life flight plans from the perspective of what data they contain and how it is used. They are an important part in keeping track of the individual flights through the airspace (and also serve the law enforcement and military in keeping track of unannounced/suspicious flights :wink: ).

It seems it can be seen as three categories of information of which one is not of that much interest in FlightGear. Those three categories are:

  • Information about the aircraft: Callsign, tail number (if different from the callsign), navigation and communication equipment, number of aircraft (when the flight consist of several aircraft in formation, e.g. military ferry flights), commander etc.
  • Route information (In essence what people usually refers to with "flight plan"): Departure and destination airport, date and times, route, cruise altitude and airspeed, IFR, VFR or mixed flight rules etc.
  • Search and rescue information: Number of passengers, survival equipment, aircraft colours, dinghy type and colours, fuel endurance etc. (This is the category of information that is probably less relevant in FlightGear as crashed aircraft usually respawn at the nearest or departure airport).
The filing of a flight plan is only a part of handling flight plans, and flight plans themselves are today complex enough (mostly due to the rich variation in nav and com equipment) that a "wizard" to help filling the form when done online (which is often promoted) seems to be less and less uncommon.

Filing of the flight plan also is just a small step in in the handling of the flight plan. In a similar way to how it is serialised into text strings (probably since the day of teleprinters), activation, amendments, updates, changes and termination is probably done as well, though I have not come that far yet.
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Re: Transponder over network

Postby Omega » Fri May 10, 2013 10:49 pm

wagnerw,

Thanks for updating us with your thoughts.
To answer your questions, first you have to keep in mind that today's radar facilities use computers to display the radar image to the controller. Therefore, the squawk codes are assigned just like in any vatsim client, the controller selects the target with his track pad, hits a button on his keyboard and the computer returns a squawk value.

Now, each facility has certain squawk code ranges. For example, a facility can assign squawk codes between the 0701-0734 range.

To address the .pof files, those can be downloaded from any vACC/ARTCC's vatsim website, often they will also include sector files with them.
The coding structure of the files is very simple and understanding, but it uses the callsign and primary frequency of the facility to "calibrate" the squawk code ranges available to each respective ATC client.
If we were to use these files just like how they are, without any modifications, we can probably tell OpenRadar to just look for the callsign of the facility (which will be probably inputted through a respective textbox within the OpenRadar GUI, since several of the call-signs in the pof files contain greater than 7 characters :wink: ) + (which I'm just guessing whether will be possible or not, since I've nil experience with java).
Most of the pof files are not licensed and I don't think this will be a problem, as long as we don't do any modifications to them and/or republish them. So, the users can simply download those files from the vACC's website and import them into OpenRadar.

The other solution is of course to make our own pof files with some kind of similar format and then base the squawk code ranges to the actual pof files.
wagnerw wrote:Omega, how comes the aircraft type into the game? Is it delivered with the flightplan? How does it work in real live? Flightplan filed under Callsign and Flightnumber => Contact identifies itself => ATC tells Contact Squawk code and assigns it to flightplan?

I haven't read much about flight briefing in real life but after some research it should probably be delivered from the flightplan that is entered into a system, then the clearance delivery person can access it and so on...
wagnerw wrote:Do we really want to force everybody to file a flightplan, before he can fly at your airports? Or do we alternatively accept anything flightplan like be it per chat or voice. In the later more beginner friendly way, we could keep it more simple...

It'd be really nice to have such a feature for people that do want to file a flightplan, if they don't want to we can file it for them and that actually does happen in real life as well.
If an aircraft is flying (mostly VFR) in some uncontrolled airspace then tries to contact ATC prior entering a controlled airspace, the identification of the target was not handed off so the pilot has to advice the controller of his position, where he is going, aircraft type and his route/intentions. Then a squawk code will be re-assigned and the aircraft can continue with radar services.

If you have any more questions, I'd be more than happy to assist.
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Re: Transponder over network

Postby wagnerw » Sat May 11, 2013 6:02 am

Good morning,

Would you please provide me an URL, where I can download a sample POF file? I am not sure, if we have to ask somebody before we use those files... I don't want to simply use files, as they are published, if we don't get the rights to do so. Even, if the user does it and not me.

This feature seems to be straight forward... Main point to stress is to equip all the planes with a transponder...

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Re: Transponder over network

Postby F-JJTH » Sat May 11, 2013 10:15 am

Hi all,

The new transponder system is not yet ready. The code added by James in the repo is wrong IMO because not realistic at all for now.

@Wolfram: Vivian plan to add a generic transponder in the GUI, in this way every aircraft could have a working transponder

Image

For now the code added in GIT doesn't work as expected for example : http://clemaez.fr/flightgear/Screenshot ... orking.png
In this screenshot I transmit sqwak -9999 from one aircraft (which is totally impossible in real world... so not realistic) and the other aircraft receive -9998 (which is certainly a bug) Also the first aircraft is transmitting sqwak -9999 even if the transponder is OFF or SBY... I need to talk with James about all of this.

My original work ( working and realistic ) still here : https://gitorious.org/~f-jjth/fg/f-jjth ... 6ab0369a28

Cheers,
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