wrappingS-SENSOR-ACCEL.js File Reference

Wrappers for the Accelerometer Sensor, LinearAccelerationSensor, and GravitySensor. More...

Classes
class	DataGenerator

Functions
function	shake (axis)
function	updateReadings (sensorObject)

Variables
var	previousReading
var	emulateStationaryDevice = (typeof args === 'undefined') ? true : args[0]
var	debugMode = false
const	TWOPI = 2 * Math.PI
var	orig_getters
var	origGetY = Object.getOwnPropertyDescriptor(Accelerometer.prototype, "y").get
var	origGetZ = Object.getOwnPropertyDescriptor(Accelerometer.prototype, "z").get
var	origGetTimestamp = Object.getOwnPropertyDescriptor(Sensor.prototype, "timestamp").get
var	generators
var	helping_functions
var	hc = init_data + orig_getters + helping_functions + generators
var	wrappers

Detailed Description

Wrappers for the Accelerometer Sensor, LinearAccelerationSensor, and GravitySensor.

See also

https://www.w3.org/TR/accelerometer/

https://www.w3.org/TR/accelerometer/#linearaccelerationsensor

https://www.w3.org/TR/accelerometer/#gravitysensor

Author

Copyright (C) 2021 Radek Hranicky

License:

SPDX-License-Identifier: GPL-3.0-or-later

MOTIVATION Readings from the Accelerometer, LinearAccelerationSensor, and GravitySensor of the Generic Sensor API should be secured as they provide a potentially valuable data for creating fingerprints. There are multiple options. A unique fingerprint can be obtained by describing the device's vibrations (See https://link.springer.com/chapter/10.1007/978-3-319-30806-7_7). Using trajectory inference and matching of the model to map data, one may use the readings from the Accelerometer to determing the device's position (See https://www.researchgate.net/publication/220990763_ACComplice_Location_ inference_using_accelerometers_on_smartphones). Accelerometer readings can also be used for determining human walking patterns (See https://www.researchgate.net/publication/322835708_Classifying_Human_ Walking_Patterns_using_Accelerometer_Data_from_Smartphone).

WRAPPING The wrapper replaces the "XYZ" getters of the Accelerometer sensor, LinearAccelerationSensor, and GravitySensor. The wrapping's goal is to simulate a stationary device that can be possibly rotated. The rotation of the device is represented by the fake rotation matrix "orient.rotMat".

The GravitySensor should provide readings of gravity acceleration applied to the device. This is represented by a vector made of x, y, z portions. To get this faked gravity vector for the device, the reference vector [0, 0, 9.8] is multipled with the rotation matrix. Wrappers for the GravitySensor's getters return x, y, z portions of the fake gravity vector.

Next, the LinearAccelerationSensor should return acceleration values without the contribution of gravity. For a stationary device, it should be all zeroes. Yet, there could be vibrations that may change values a little bit, e.g., spin around -0.1 to +0.1, as seen on the examined devices. This usually does not happed with every reading but only in intervals of seconds. And thus, after a few seconds we pseudo-randomly change these values.

Finally, the Accelerometer sensor combines the previous two. Our wrappers thus return tha values from the LinearAccelerationSensor with the fake gravity vector portions added.

POSSIBLE IMPROVEMENTS Support for simulation of a non-stationary device where the rotation can change. Currently, the calculation of the gravity vector is done only once by the initDataGenerator() where the reference vector is multiplied with the rotation matrix. If orient.rotMat could change, the dataGen would have to be updated periodically. Moreover, such a change should also be taken into account in wrappers for other movement-related sensors (Gyroscope, etc.).

Function Documentation

shake()

function shake

(

axis

)

Here is the call graph for this function:

updateReadings()

function updateReadings

(

sensorObject

)

Variable Documentation

debugMode

var debugMode = false

emulateStationaryDevice

var emulateStationaryDevice = (typeof args === 'undefined') ? true : args[0]

generators

var generators

Initial value:

= `
    
    var dataGenerator = dataGenerator || new DataGenerator()

hc

var hc = init_data + orig_getters + helping_functions + generators

helping_functions

var helping_functions

Initial value:

= sensorapi_prng_functions + device_orientation_functions
      + DataGenerator + shake + updateReadings

orig_getters

var orig_getters

Initial value:

= `
    var origGetX = Object.getOwnPropertyDescriptor(Accelerometer.prototype, "x").get

origGetTimestamp

var origGetTimestamp = Object.getOwnPropertyDescriptor(Sensor.prototype, "timestamp").get

origGetY

var origGetY = Object.getOwnPropertyDescriptor(Accelerometer.prototype, "y").get

origGetZ

var origGetZ = Object.getOwnPropertyDescriptor(Accelerometer.prototype, "z").get

previousReading

var previousReading

Initial value:

= previousReading || {orig_x: null, orig_y: null, orig_z: null, timestamp: null,
                      fake_x: null, fake_y: null, fake_z: null, gVector: null}

TWOPI

const TWOPI = 2 * Math.PI

wrappers

var wrappers