When a motorist enters an overpass that runs parallel to a ground-level road, it's possible that their GPS navigation system will think that they're still on the lower road. As a result, the system will issue incorrect instructions. A new system created at the University of Hong Kong is designed to keep that from happening.

Known as the Angle Difference Method, the system was developed by a team led by Prof. Anthony Yeh Gar-On. It utilizes an in-vehicle smartphone running a navigation app, which is linked by Bluetooth to the car's built-in or plug-in onboard diagnostic device. The angle at which the phone is mounted doesn't matter, as an initial calibration process that is performed on level ground compensates for it.

When the car enters the on-ramp for an overpass, the system automatically detects the change in the vehicle's inclination. It compares that angle to the angle that the car should be at, if it's on the correct road – that information is available in online geographic information systems.

If it's determined that the driver has entered the overpass in error, the app instantly alerts them to the fact. And even if they're supposed to be on it, the navigation system won't mistakenly think that they're still on the ground-level road that they actually exited.

"The invention provides an innovative, simple, and inexpensive method to overcome the long-existing vehicle navigation problem that many people have tried to solve since GPS was used over 20 years ago, by determining instantly whether a vehicle has entered a flyover [overpass] or still on the ground level," says Prof. Yeh. "The research team will further apply this Angle Difference Method to the navigation of automatic cars."

The university has patented the technology, and is now looking for industry parters that are interested in commercializing it.

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