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The Motion Blog/Sharing insights from our research on motion.


Detecting how you hold your phone

Accelerometers measure everything that moves, providing developers with a wealth of information about the motion state of a mobile device over time. However, extracting usefull information from this noisy data stream can be challanging. This article describes a technique for determining the positions that a device is held by observing the gravitational forces applied to its x,y and z axes.


The combined force exerted upon the x,y and z axes of a device is calculated by the distance function: SquareRoot(x^2 + y^2 +z^2). When the device is not accelerating, this function evaluates to the force of gravity (~9.85). This property ensures that when a correctly calibrated device is not in motion,the  x,y,z accelerometer readings that it provides, will plot to points on a sphere with radius ~9.85. 



670 sample data points collected from an accelerometer stream during approximately 2 minutes, while the device was held in portrait, landscape and face-up positions. 


Notice that the plotted x,y,z coordinates of each accelerometer event appear as points on the sphere.


By mapping the points to areas on the surface of the sphere it is possible to determine how the device is being held in a user's hand.


Notice in the diagram below how the G series digresses from 9.85 to co-incide with transitions between hand held positions. When a device is in motion, gravity is not the only acceleration force that is being applied to the device.


Time series of X,Y,Z accelerometer readings and G value calculated by the distance function for the same data stream

that is presented above..


A phone's capability to be aware of how it is being held in a user's hand can be exploited for various applications

including provision of more intuitive and responsive user interfaces.


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geoffk's picture
What other applications can you think of that can benefit from a device's capability to recognize how it is being held ?