Ronan McGurren, geographic analyst with Navteq, said that, as the tunnel is over four kilometres long, it is not possible to rely on GPS signals to give a position reading, so a specially equipped car was brought over from Paris to complete the job. The car features an Inertia Measuring Unit which relies on ‘dead reckoning’ – the same principle used by Christopher Columbus when sailing to America! The difference is this sophisticated unit calculates the position of the vehicle 200 times per second and is accurate to less than a few feet, whereas Columbus calculated his position once a day and could easily be several miles out.
A gyroscope in the unit gauges the direction of the vehicle whilst an odometer measures the distance travelled; by relating this information to the starting point, the current position can be calculated. Once you know where the vehicle is, an accurate trace of the road can be created even in the deepest tunnel.
In addition to this more traditional method of ‘positioning’, the Navteq team used the same system and specialist software to create this new section of map. Developed exclusively for the job, the software enables the field teams to download sections of the live database to a mobile computer for updating on the road. Travelling in pairs, the person not driving constantly talks to the computer via a headset, noting all the changes as they travel.
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