Most of us rarely question the accuracy of the GPS dot that shows our location on a map.
Yet when visiting a new city and using our phone to navigate, it can seem as if we are jumping from one spot to another, even though we are walking steadily along the same sidewalk.
"Cities are brutal for satellite navigation," explained Ardeshir Mohamadi.
Mohamadi, a doctoral fellow at the Norwegian University of Science and Technology (NTNU), is researching how to make affordable GPS receivers (like those found in smartphones and fitness watches) much more precise without depending on expensive external correction services.
High accuracy is especially vital for vehicles that drive themselves - autonomous or self-driving cars.
Urban canyons
Mohamadi and his team at NTNU have developed a new system that allows autonomous vehicles to navigate safely through dense city environments.
"In cities, glass and concrete make satellite signals bounce back and forth. Tall buildings block the view, and what works perfectly on an open motorway is not so good when you enter a built-up area," said Mohamadi.
When GPS signals reflect off buildings, they take longer to reach the receiver. This delay throws off the calculation of distance to the satellites, which makes the reported position inaccurate.
Such complex urban environments are known as 'urban canyons'. It is similar to being at the bottom of a deep gorge, where signals reach you only after multiple reflections from the walls.
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