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Underground Metro Mapping

Underground Mapping with Tunnel GNSS

The subject of Underground Mapping would be looking at systems to accurately trace and map underground pipelines, ducts and tunnels. These systems tend to be autonomous, so no personnel need to work underground.

In mining/seismic work where access is not an issue, LiDAR (Light Detection and Ranging) systems produce astounding 3D models.

These are not the subject of this Bitesize article. Our skills lie in navigation and timing using GPS and other GNSS systems and so we are focusing on mapping underground systems with Tunnel GPS. Simulated satellite signals that allows standard GPS receivers to determine their position as if they had a view of the sky.

Metro and Road Tunnels

Tunnel GPS builds a simulated satellite navigation data based on local surface location. This allows it to deliver a signal as if a sky view were available. This is not just repeating the surface GPS/GNSS data and transmitting simulated satellite vehicle data as if the sky was visible. For example, locating you 15 metres under Old Street rather than on Old Street itself.

Likewise, in a road tunnel these signals can give actual location. Not so important in the vast majority of tunnels with just a single entry and exit. However, for more complex tunnels with one or more junctions underground they will allow easy navigation.

Radio Signal Surveys

Tunnel GPS systems can use existing communications systems in road and metro tunnels to deliver the simulated satellite signals. These are usually ‘leaky feeder’ systems delivering various radio signals such as emergency services and mobile networks. Commissioning such a radio system will require some surveyed reference points. This includes a simple commissioning process using handheld GNSS devices feeding data back into the simulation system. This will ensure accurate simulated data is transmitted.

Mapping Solutions

One of the real advantages of a Tunnel GNSS system is that the signals can be used by standard GPS receivers, such as those built into all smartphones. For work and safety systems in metros and mining for example, the Tunnel GNSS data can easy be integrated into existing systems including mapping.

In the case of a road tunnel, these will be available on public mapping solutions (Google, Apple, Here) even if their below ground elevation is not that important. You should at least be able to find the right junctions though using Tunnel GPS.

For public use, most mapping solutions have not really been concerned with underground metro locations, but this will not always be the case, especially at station locations. Systems such as E112 in the EU, which mandates location data as part of calls to emergency services, are being introduced.


For industrial and commercial applications, the ability to use Tunnel GPS with existing systems is already a relatively simple option. The opportunity for these systems to integrate into widely available mapping solutions, perhaps alongside or in conjunction with Bluetooth or other augmentation systems, could bring the same benefits of these GPS systems. It is ‘the world’s largest free utility’ whether you can see the sky or not.


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