Motion detection

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Motion detection is the process of detecting a change in the position of an object relative to its surroundings or a change in the surroundings relative to an object. It can be achieved by either mechanical or electronic methods.[1] When it is done by natural organisms, it is called motion perception.

Methods[edit]

Motion can be detected by monitoring changes in:

  • Infrared light (passive and active sensors)
  • Visible light (video and camera systems)
  • Radio frequency energy (radar, microwave and tomographic motion detection)
  • Sound (microphones, other acoustic sensors)
  • Kinetic energy (triboelectric, seismic, and inertia-switch sensors)
  • Magnetism (magnetic sensors, magnetometers)
  • Wi-Fi Signals (WiFi Sensing)

Mechanical[edit]

The most basic forms of mechanical motion detection utilize a switch or trigger. For example, the keys of a typewriter use a mechanical method of detecting motion, where each key is a switch that is either off or on, and each letter that appears is a result of the key's motion.

Electronic[edit]

The principal methods by which motion can be electronically identified are optical and acoustic. Infrared light or laser technology can be used for optical detection. Motion-detection devices such as PIR motion detectors have a sensor that detects a disturbance in the infrared spectrum. A signal can then activate an alarm, and/or a camera to capture an image or video of the event.[2][3]

This method's chief applications are:

  • Detection of unauthorized entry
  • Turning lights on/off when an area is entered/vacated
  • Activating a camera to record new events (e.g. human activity)

A simple algorithm for motion detection by a fixed camera compares the current image with a reference image and monitors the number of different pixels. Since images naturally differ due to factors such as varying lighting, camera flicker, and CCD dark currents, pre-processing is useful to reduce the number of false positive alarms.

More complex algorithms are necessary to detect motion when the camera itself is panning, or when a specific object's motion must be detected in a field containing other, irrelevant movement—for example, a painting surrounded by visitors in an art gallery. With a panning camera, models based on optical flow are used to distinguish between apparent background motion caused by the camera's movement and that of independently moving objects.[4]

Devices[edit]

Motion detectors are often integrated components of systems that automatically perform tasks, or alert users of motion in an area. An occupancy sensor detects the entry or movement of a person or thing within a certain space.

Motion controllers are also used for video game consoles as game controllers. A camera can also allow the body's movements to be used for control, such as in the Kinect system.

References[edit]

  1. ^ "motion detection". Retrieved 26 January 2015.
  2. ^ Video motion detection (VMD) Archived 2011-10-23 at the Wayback Machine
  3. ^ Mechanisms of visual motion
  4. ^ Bewley, A., Guizilini, V., Ramos, F., & Upcroft, B. (2014). Online Self-Supervised Multi-Instance Segmentation of Dynamic Objects. In International Conference on Robotics and Automation (pp. 1296–1303). Hong Kong, China: IEEE. doi:10.1109/ICRA.2014.6907020

External links[edit]