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quartz/content/notes/10-orientation-sensors.md
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title tags
10-orientation-sensors
lecture
info305

Accelerometers

  • Measures proper acceleration (acceleration it experiences relative to freefall. gravity), felt by people or objects
  • Units: m/s2 or g
  • Most smartphone accelerometers trade large value range for high precision
    • iPhone range: ±2g, precision 0.018g g forces|300

Accelerometers

  • Acceleration is measured on 3 axes
  • Orientation of sensor (and coordinate system) varies among different device |100

Accelerometers

  • Miniaturisation using a MEMS (Microelectromechanical systems)
  • Measuring flowing current over an differential capacitor indicates the acceleration |300

Accelerometers

  • Advantage:
    • Fast update rate
    • Relatively accurate
  • Disadvantage:
    • Can’t easily identify certain kind of acceleration (small value range)

Compass / Magnetometer

  • Measures the strength of earth’s magnetic field
  • Strength is expressed in tesla [T]
  • iPhone 4 magnetometer range: ±2mT
  • Pro tip: prolonged exposure to a fridge magnet decalibrates your phones’ magnetometer for at least a week ;-) field strength examples|300

Error around metal/magnetic objects

Recap

  • Several improvements to traditional GPS

  • AGPS for improved startup time and improved localisation using WIFI

  • DGPS for improved localisation using reference stations with known error

  • RTK GPS for improve localisation using DGPS and phase analysis

  • Accelerometers for measuring gravity along multiple axis (typically 3)

  • Usually implemented with MEMS

  • Typically limited in value range (in mobile devices)