Frequently Asked Questions - Sensor Readout

Similar to magnetometer but the hard iron calibration (device calibration due to distortions that arise from magnetized iron, steel or permanent magnets on the device) is not considered in the given sensor values.

Also, no periodic calibration is performed (i.e. there are no discontinuities in the data stream while using this sensor) and assumptions that the magnetic field is due to the Earth's poles is avoided, but factory calibration and temperature compensation have been performed.

Computes the device's orientation based on the rotation matrix. This type of sensor is often used in games to react on how the player holds the phone.

This sensor simply plots the ambient temperature in °C. Like the humidity and pressure sensor, it is used in environmental apps.

Measures the acceleration force in m/s² that is applied to a device on all three physical axes (x, y, and z), excluding the force of gravity.

A sensor of this type measures the force of gravity in m/s2 that is applied to a device on all three physical axes (x, y, z).

The coordinate system is the same as is used by the acceleration sensor.

Note: When the device is at rest, the output of the gravity sensor should be identical to that of the accelerometer.

A sensor of this type measures distance. The proximity sensor is typically located next to the speaker of a phone and used to turn the display off when the user is using the telephone.

Most phones come with very cheap proximity sensors that can only distinguish between a NEAR ("covered") and a FAR ("not covered") state. Such sensors will only report to values: zero and whatever they consider to be FAR (in centimeters). It is possible that the readout of this sensor will overlap with the X-Axis, making it hard to see.

A sensor of this type measures the ambient air pressure in hPa or mbar. A barometer is typically used to support the GPS module. Knowing the current altitude of the phone allows for calculating the current position faster.

A light sensor measures ambient light in SI lux. It is commonly used to control screen brightness and is usually located in the vicinity of the user facing camera.

Light sensors often have poor resolution. In dark rooms, it is possible that their plot will overlap with the X-axis, making it hard to see.

A gyroscope measures rotation.

All values are in radians/second and measure the rate of rotation around the device's local X, Y and Z axis. The coordinate system is the same as is used for the acceleration sensor. Rotation is positive in the counter-clockwise direction. That is, an observer looking from some positive location on the x, y or z axis at a device positioned on the origin would report positive rotation if the device appeared to be rotating counter clockwise. Note that this is the standard mathematical definition of positive rotation and does not agree with the definition of roll given earlier.

A sensor of this type measures magnetic field strength. All values are in micro-Tesla (uT) and measure the ambient magnetic field in the X, Y and Z axis.

A sensor of this type measures the acceleration applied to the device (Ad). Conceptually, it does so by measuring forces applied to the sensor itself (Fs) using the relation:

Ad = - ∑Fs / mass

In particular, the force of gravity is always influencing the measured acceleration:

Ad = -g - ∑F / mass

For this reason, when the device is sitting on a table (and obviously not accelerating), the accelerometer reads a magnitude of g = 9.81 m/s^2

Similarly, when the device is in free-fall and therefore dangerously accelerating towards to ground at 9.81 m/s^2, its accelerometer reads a magnitude of 0 m/s^2.