SensorEvent
public
class
SensorEvent
extends Object
java.lang.Object  
↳  android.hardware.SensorEvent 
This class represents a Sensor
event and
holds information such as the sensor's type, the timestamp, accuracy and of
course the sensor's data
.
Definition of the coordinate system used by the SensorEvent API.
The coordinatesystem is defined relative to the screen of the phone in its default orientation. The axes are not swapped when the device's screen orientation changes.
The X axis is horizontal and points to the right, the Y axis is vertical and points up and the Z axis points towards the outside of the front face of the screen. In this system, coordinates behind the screen have negative Z values.
Note: This coordinate system is different from the one used in the Android 2D APIs where the origin is in the topleft corner.
See also:
Summary
Fields  

public
int 
accuracy
The accuracy of this event. 
public
Sensor 
sensor
The sensor that generated this event. 
public
long 
timestamp
The time in nanosecond at which the event happened 
public
final
float[] 
values
The length and contents of the 
Inherited methods  

From
class
java.lang.Object

Fields
accuracy
int accuracy
The accuracy of this event. See SensorManager
for details.
sensor
Sensor sensor
The sensor that generated this event. See
SensorManager
for details.
values
float[] values
The length and contents of the values
array depends on
which sensor
type is being monitored (see
also SensorEvent
for a definition of the coordinate system used).
Sensor.TYPE_ACCELEROMETER
:
All values are in SI units (m/s^2)
 values[0]: Acceleration minus Gx on the xaxis
 values[1]: Acceleration minus Gy on the yaxis
 values[2]: Acceleration minus Gz on the zaxis
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:
In particular, the force of gravity is always influencing the measured acceleration:
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 freefall and therefore dangerously accelerating towards to ground at 9.81 m/s^2, its accelerometer reads a magnitude of 0 m/s^2.
It should be apparent that in order to measure the real acceleration of the device, the contribution of the force of gravity must be eliminated. This can be achieved by applying a highpass filter. Conversely, a lowpass filter can be used to isolate the force of gravity.
public void onSensorChanged(SensorEvent event) { // alpha is calculated as t / (t + dT) // with t, the lowpass filter's timeconstant // and dT, the event delivery rate final float alpha = 0.8; gravity[0] = alpha * gravity[0] + (1  alpha) * event.values[0]; gravity[1] = alpha * gravity[1] + (1  alpha) * event.values[1]; gravity[2] = alpha * gravity[2] + (1  alpha) * event.values[2]; linear_acceleration[0] = event.values[0]  gravity[0]; linear_acceleration[1] = event.values[1]  gravity[1]; linear_acceleration[2] = event.values[2]  gravity[2]; }
Examples:
 When the device lies flat on a table and is pushed on its left side toward the right, the x acceleration value is positive.
 When the device lies flat on a table, the acceleration value is +9.81, which correspond to the acceleration of the device (0 m/s^2) minus the force of gravity (9.81 m/s^2).
 When the device lies flat on a table and is pushed toward the sky with an acceleration of A m/s^2, the acceleration value is equal to A+9.81 which correspond to the acceleration of the device (+A m/s^2) minus the force of gravity (9.81 m/s^2).
Sensor.TYPE_MAGNETIC_FIELD
:
All values are in microTesla (uT) and measure the ambient magnetic field
in the X, Y and Z axis.
Sensor.TYPE_GYROSCOPE
:
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
counterclockwise 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.
 values[0]: Angular speed around the xaxis
 values[1]: Angular speed around the yaxis
 values[2]: Angular speed around the zaxis
Typically the output of the gyroscope is integrated over time to calculate a rotation describing the change of angles over the time step, for example:
private static final float NS2S = 1.0f / 1000000000.0f; private final float[] deltaRotationVector = new float[4](); private float timestamp; public void onSensorChanged(SensorEvent event) { // This time step's delta rotation to be multiplied by the current rotation // after computing it from the gyro sample data. if (timestamp != 0) { final float dT = (event.timestamp  timestamp) * NS2S; // Axis of the rotation sample, not normalized yet. float axisX = event.values[0]; float axisY = event.values[1]; float axisZ = event.values[2]; // Calculate the angular speed of the sample float omegaMagnitude = sqrt(axisX*axisX + axisY*axisY + axisZ*axisZ); // Normalize the rotation vector if it's big enough to get the axis if (omegaMagnitude > EPSILON) { axisX /= omegaMagnitude; axisY /= omegaMagnitude; axisZ /= omegaMagnitude; } // Integrate around this axis with the angular speed by the time step // in order to get a delta rotation from this sample over the time step // We will convert this axisangle representation of the delta rotation // into a quaternion before turning it into the rotation matrix. float thetaOverTwo = omegaMagnitude * dT / 2.0f; float sinThetaOverTwo = sin(thetaOverTwo); float cosThetaOverTwo = cos(thetaOverTwo); deltaRotationVector[0] = sinThetaOverTwo * axisX; deltaRotationVector[1] = sinThetaOverTwo * axisY; deltaRotationVector[2] = sinThetaOverTwo * axisZ; deltaRotationVector[3] = cosThetaOverTwo; } timestamp = event.timestamp; float[] deltaRotationMatrix = new float[9]; SensorManager.getRotationMatrixFromVector(deltaRotationMatrix, deltaRotationVector); // User code should concatenate the delta rotation we computed with the current rotation // in order to get the updated rotation. // rotationCurrent = rotationCurrent * deltaRotationMatrix; }
In practice, the gyroscope noise and offset will introduce some errors which need to be compensated for. This is usually done using the information from other sensors, but is beyond the scope of this document.
Sensor.TYPE_LIGHT
:
 values[0]: Ambient light level in SI lux units
Sensor.TYPE_PRESSURE
:
 values[0]: Atmospheric pressure in hPa (millibar)
Sensor.TYPE_PROXIMITY
:
 values[0]: Proximity sensor distance measured in centimeters
Note: Some proximity sensors only support a binary near or
far measurement. In this case, the sensor should report its
maximum range
value in
the far state and a lesser value in the near state.
Sensor.TYPE_GRAVITY
:
A three dimensional vector indicating the direction and magnitude of gravity. Units are m/s^2. 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.
Sensor.TYPE_LINEAR_ACCELERATION
:
A three dimensional vector indicating acceleration along each device axis, not including
gravity. All values have units of m/s^2. The coordinate system is the same as is used by the
acceleration sensor.
The output of the accelerometer, gravity and linearacceleration sensors must obey the following relation:
 acceleration = gravity + linearacceleration
Sensor.TYPE_ROTATION_VECTOR
:
The rotation vector represents the orientation of the device as a combination of an angle and an axis, in which the device has rotated through an angle θ around an axis <x, y, z>.
The three elements of the rotation vector are <x*sin(θ/2), y*sin(θ/2), z*sin(θ/2)>, such that the magnitude of the rotation vector is equal to sin(θ/2), and the direction of the rotation vector is equal to the direction of the axis of rotation.
The three elements of the rotation vector are equal to the last three components of a unit quaternion <cos(θ/2), x*sin(θ/2), y*sin(θ/2), z*sin(θ/2)>.Elements of the rotation vector are unitless. The x,y, and z axis are defined in the same way as the acceleration sensor.
The reference coordinate system is defined as a direct orthonormal basis, where: X is defined as the vector product Y.Z (It is tangential to the ground at the device's current location and roughly points East).
 Y is tangential to the ground at the device's current location and points towards magnetic north.
 Z points towards the sky and is perpendicular to the ground.
 values[0]: x*sin(θ/2)
 values[1]: y*sin(θ/2)
 values[2]: z*sin(θ/2)
 values[3]: cos(θ/2)
 values[4]: estimated heading Accuracy (in radians) (1 if unavailable)
values[3], originally optional, will always be present from SDK Level 18 onwards. values[4] is a new value that has been added in SDK Level 18.
Sensor.TYPE_ORIENTATION
:
All values are angles in degrees.
 values[0]: Azimuth, angle between the magnetic north direction and the
yaxis, around the zaxis (0 to 359). 0=North, 90=East, 180=South,
270=West
values[1]: Pitch, rotation around xaxis (180 to 180), with positive values when the zaxis moves toward the yaxis.
values[2]: Roll, rotation around the yaxis (90 to 90) increasing as the device moves clockwise.
Note: This definition is different from yaw, pitch and roll used in aviation where the X axis is along the long side of the plane (tail to nose).
Note: This sensor type exists for legacy reasons, please use
rotation vector sensor type
and
getRotationMatrix()
in conjunction with
remapCoordinateSystem()
and
getOrientation()
to
compute these values instead.
Important note: For historical reasons the roll angle is positive in the clockwise direction (mathematically speaking, it should be positive in the counterclockwise direction).
Sensor.TYPE_RELATIVE_HUMIDITY
:
 values[0]: Relative ambient air humidity in percent
When relative ambient air humidity and ambient temperature are measured, the dew point and absolute humidity can be calculated.
Dew PointThe dew point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to condense into water.
ln(RH/100%) + m·t/(T_{n}+t) t_{d}(t,RH) = T_{n} ·  m  [ln(RH/100%) + m·t/(T_{n}+t)]
 t_{d}
 dew point temperature in °C
 t
 actual temperature in °C
 RH
 actual relative humidity in %
 m
 17.62
 T_{n}
 243.12 °C
for example:
h = Math.log(rh / 100.0) + (17.62 * t) / (243.12 + t); td = 243.12 * h / (17.62  h);Absolute Humidity
The absolute humidity is the mass of water vapor in a particular volume of dry air. The unit is g/m^{3}.
RH/100%·A·exp(m·t/(T_{n}+t)) d_{v}(t,RH) = 216.7 ·  273.15 + t
 d_{v}
 absolute humidity in g/m^{3}
 t
 actual temperature in °C
 RH
 actual relative humidity in %
 m
 17.62
 T_{n}
 243.12 °C
 A
 6.112 hPa
for example:
dv = 216.7 * (rh / 100.0 * 6.112 * Math.exp(17.62 * t / (243.12 + t)) / (273.15 + t));
Sensor.TYPE_AMBIENT_TEMPERATURE
:
 values[0]: ambient (room) temperature in degree Celsius.
Sensor.TYPE_MAGNETIC_FIELD_UNCALIBRATED
:
Similar to TYPE_MAGNETIC_FIELD
,
but the hard iron calibration is reported separately instead of being included
in the measurement. Factory calibration and temperature compensation will still
be applied to the "uncalibrated" measurement. Assumptions that the magnetic field
is due to the Earth's poles is avoided.
The values array is shown below:
 values[0] = x_uncalib
 values[1] = y_uncalib
 values[2] = z_uncalib
 values[3] = x_bias
 values[4] = y_bias
 values[5] = z_bias
x_uncalib, y_uncalib, z_uncalib are the measured magnetic field in X, Y, Z axes. Soft iron and temperature calibrations are applied. But the hard iron calibration is not applied. The values are in microTesla (uT).
x_bias, y_bias, z_bias give the iron bias estimated in X, Y, Z axes. Each field is a component of the estimated hard iron calibration. The values are in microTesla (uT).
Hard iron  These distortions arise due to the magnetized iron, steel or permanent magnets on the device. Soft iron  These distortions arise due to the interaction with the earth's magnetic field.
TYPE_GAME_ROTATION_VECTOR
:
Identical to TYPE_ROTATION_VECTOR
except that it
doesn't use the geomagnetic field. Therefore the Y axis doesn't
point north, but instead to some other reference, that reference is
allowed to drift by the same order of magnitude as the gyroscope
drift around the Z axis.
In the ideal case, a phone rotated and returning to the same realworld
orientation will report the same game rotation vector
(without using the earth's geomagnetic field). However, the orientation
may drift somewhat over time. See TYPE_ROTATION_VECTOR
for a detailed description of the values. This sensor will not have
the estimated heading accuracy value.
Sensor.TYPE_GYROSCOPE_UNCALIBRATED
:
All values are in radians/second and measure the rate of rotation
around the X, Y and Z axis. An estimation of the drift on each axis is
reported as well.
No gyrodrift compensation is performed. Factory calibration and temperature compensation is still applied to the rate of rotation (angular speeds).
The coordinate system is the same as is used for the
TYPE_ACCELEROMETER
Rotation is positive in the counterclockwise direction (righthand rule).
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.
The range would at least be 17.45 rad/s (ie: ~1000 deg/s).
 values[0] : angular speed (w/o drift compensation) around the X axis in rad/s
 values[1] : angular speed (w/o drift compensation) around the Y axis in rad/s
 values[2] : angular speed (w/o drift compensation) around the Z axis in rad/s
 values[3] : estimated drift around X axis in rad/s
 values[4] : estimated drift around Y axis in rad/s
 values[5] : estimated drift around Z axis in rad/s
Pro Tip: Always use the length of the values array while performing operations on it. In earlier versions, this used to be always 3 which has changed now.
Interfaces
Classes