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IMU Notes

Under construction 🏗️

Info

Every 3 months, I wrangle with IMU data for 2 weeks and promptly forget the nitty gritty. I'm really just writing notes to my future self here.

For a quick review on outputs, see link

  • IMU orientation is w.r.t a local ENU frame. This is a moving frame centered around the IMU with gravity aligned Z-axis
  • Heading accuracy depends on magnetometer. The Y-axis is fixed to North, Z to gravity. Measurements will be affected if the IMU comes near ferromagnetic material
    • If no magnetometer, orientation will constantly change. See link
  • Acceleration measurements are affected by engine vibrations and road surface
  • IMU might be mounted upside down on vehicle. It's drivers may-or-may-not be configured to handle this correctly
  • When using a RTK/INS system like OxTS, the GNSS and IMU systems are usually oriented separately.
    • IMU might have the +Z axis pointing down but GNSS altitude is always pointing up