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SENSORS · POSITIONING

What Is an IMU?

An IMU (inertial measurement unit) is a sensor that measures acceleration and rotation, usually with accelerometers and gyroscopes on three axes, and often a magnetometer. From those readings a system can work out its orientation and movement. Combined with GNSS, an IMU keeps positioning accurate and continuous, even when satellite signals drop out.

01

The Short Answer

GNSS alone gives absolute position but loses it in tunnels, deep cuttings and under bridges. An IMU tracks movement between fixes, a technique called dead reckoning, and fusing the two gives a smooth, continuous position that a mapping or inspection system can rely on.

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    Bridging gaps Keeps position through tunnels and urban canyons.
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    Orientation Tells the system which way cameras and sensors are pointing.
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    Smoothing Fills in between GNSS updates for steady tracking.
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    Motion data Records shocks and vibration along the route.
02

Why It Matters

Our GNSS vs GPS FAQ and RTK GPS FAQ cover satellite positioning, and our sensor fusion FAQ explains combining sensors. The railway track inspection case study uses GNSS and IMU cards inside a railway computer.