About OGN

About

The goal of this project is to create a unified platform for tracking aircraft equipped with FLARM (or FLARM-compatible) emitters and OGN trackers. FLARM is mainly utilized in gliders, however other small aircraft (planes, helicopters) are often equipped with it as well, especially if operating in the areas intensively exploited by gliders (e.g. the Alps).

From OGN perspective FLARM is just a source of positioning information. We are not interested in its collision detection aspects, we are not using any of its algorithms. FLARM publishes on publicly available frequencies and OGN receivers simply listen and decode received packets. In addition to FLARM decoding, some work within our group is currently focused on creating a cheap OGN tracker, which could be installed where FLARM is not available. OGN tracker uses Open Tracking Protocol (OGNTP) and OGN receivers should be able to decode packets from both FLARM devices and OGN trackers.

A bit of a history of the project.

Motivation

We do it because we are passionate about aviation (and soaring in particular) and because it makes lot of fun!
Among us there are people of different professions and skills. What brings us all together is our passion for gliding! Everyone can join and everyone who joins brings in something that makes OGN better and better!

With constantly increasing reception coverage we hope to improve safety in the areas where glider traffic interacts with "big" aviation, leading into occasional incidents. Since normally controllers cannot see gliders on their radar screens (unless they are equipped with transponders which is not very common), OGN can propose a good alternative!
Last, but not least OGN data can help in SAR actions.

System's architecture

The present OGN architecture is set up in several tiers (layers), which interact in various ways.

ogn-topology.png

OGN Receiver tier

OGN Receiver consist of an antenna, a DVB-T stick and some sort of computer (Raspberry Pi, ODROID, BananaPi, …). Please refer to the Receiver installation section for details. The OGN receiver's antenna receives the messages broadcasted by Flarms within its reception range, the DVB-T stick processes them and the computer sends them via TCP network connection to one of the two OGN servers. The Automatic Packet Reporting System (APRS) protocol is used to exchxange data between the receiver-, infrastructure- and client-tier. There is no direct communication between OGN receivers.. All information between receivers is is exchanged via the OGN infrastructure tier.

For a detailed description of the APRS messages sent by OGN receivers, please refer to subscribing to OGN data and decoding the data section.

As the reception area of two or more OGN ground stations may overlap, the stations must synchronize all received Flarm messages in order to avoid multiple separate reports of the same Flarm device. The receivers achieve this by constantly monitoring Flarm messages received by neighboring OGN receivers. To limit bandwidth usage this monitoring activity is only done and required within a definable radius around each station. By keeping each receiver aware of traffic in its vicinity, duplicate reports about the same Flarm device are prevented.

OGN Infrastructure tier

The OGN APRS servers form the backbone of the OGN infrastructure tier. By clicking on the following links you can see all OGN receivers presently connected to the selected server.

The servers run the APRSC software, which receives all messages from the different OGN receivers and relay this information on request to the client tier. Due to load balancing and better redundancy in case of a failure there are currently three servers. They constantly exchange all received messages in order to keep the available data consistent. OGN APRS servers cache packets in memory (for few seconds) to prevent duplicates.

For more information about the APRS server software please visit following link.

Also see OGN infrastructure details.

Client tier

All available information on the OGN servers can publicly be accessed from the client tier without prior user identification. This is used by different client applications to process, visualize and analyze the APRS messages in various ways.

Live Web Page

The Live Web Page visualizes aircraft and receiver positions (extracted from APRS messages) using map overlays. The location of every FLARM/OGN tracker device presentl within reception area of the OGN network can be seen here. Only live (certain minimal system inherent time lag given) data with a short-term flight history (flight track) is provided. The tool provides no replay capability for historic flights.

Devices Database

You can influence how your glider is displayed in OGN by submitting a record into the devices database. You'll need your tracking device (e.g. FLARM) ID. By subscribing your device you can add airplane information that's displayed on live.glidernet.org, or you can opt-out from being tracked.

OGN Range Tool

The OGN Range Tool processes all APRS messages into reception range diagrams for each OGN receiver. This tool provides an overview, what areas are already within OGN network coverage. No individual flight are displayed in this tool.

SAR

For SAR and debugging purposes all APRS data is stored. This stored data is not publicly available.

XAstir

The XAstir program can be used to connect directly to one of the OGN servers and visualize APRS messages. Functionality comparable to the live web page.

For Android users

Please search for OGN Viewer in Playstore to download and install an Android App. Additionally, APRSDroid can be easily configured and used with OGN.

Own code

If you are a developer and would like to access the OGN data from your own software, please have a look at the Subscribing to OGN Data.

FLARM live range analyzer

The Flarm Live Range analyzer uses signal strength data from ground receiver stations of the OGN to analyze and visualize the transmit performance of the FLARM installation in your aircraft.

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