harmony 鸿蒙Sensor Overview

2022-08-09
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Sensor Overview

Sensor Types

Sensors in OpenHarmony are an abstraction of underlying sensor hardware. Your application can access the underlying sensor hardware via the sensors. Using the Sensor APIs, you can query sensors on your device, subscribe to sensor data, customize algorithms based on sensor data, and develop various sensor-based applications, such as compass, motion-controlled games, and fitness and health applications.

Type	Name	Description	Usage
ACCELEROMETER	Acceleration sensor	Measures the acceleration (including the gravity acceleration) applied to a device on three physical axes (X, Y, and Z), in the unit of m/s².	Detecting the motion status
ACCELEROMETER_UNCALIBRATED	Uncalibrated acceleration sensor	Measures the uncalibrated acceleration (including the gravity acceleration) applied to a device on three physical axes (X, Y, and Z), in the unit of m/s².	Measuring the acceleration bias estimation
LINEAR_ACCELERATION	Linear acceleration sensor	Measures the linear acceleration (excluding the gravity acceleration) applied to a device on three physical axes (X, Y, and Z), in the unit of m/s².	Detecting the linear acceleration in each axis
GRAVITY	Gravity sensor	Measures the gravity acceleration applied to a device on three physical axes (X, Y, and Z), in the unit of m/s².	Measuring the gravity
GYROSCOPE	Gyroscope sensor	Measures the rotation angular velocity of a device on three physical axes (X, Y, and Z), in the unit of rad/s.	Measuring the rotation angular velocity
GYROSCOPE_UNCALIBRATED	Uncalibrated gyroscope sensor	Measures the uncalibrated rotation angular velocity of a device on three physical axes (X, Y, and Z), in the unit of rad/s.	Measuring the bias estimation of the rotation angular velocity
SIGNIFICANT_MOTION	Significant motion sensor	Checks whether a device has a significant motion on three physical axes (X, Y, and Z). The value 0 means that the device does not have a significant motion, and 1 means the opposite.	Detecting significant motions of a device
PEDOMETER_DETECTION	Pedometer detection sensor	Detects whether a user takes a step. The value can be 0 (the user does not take a step) or 1 (the user takes a step).	Detecting whether a user takes a step
PEDOMETER	Pedometer sensor	Records the number of steps a user has walked.	Providing the number of steps a user has walked
AMBIENT_TEMPERATURE	Ambient temperature sensor	Measures the ambient temperature, in the unit of degree Celsius (°C).	Measuring the ambient temperature
MAGNETIC_FIELD	Magnetic field sensor	Measures the magnetic field on three physical axes (X, Y, and Z), in the unit of μT.	Creating a compass
MAGNETIC_FIELD_UNCALIBRATED	Uncalibrated magnetic field sensor	Measures the uncalibrated magnetic field on three physical axes (X, Y, and Z), in the unit of μT.	Measuring the magnetic field bias estimation
HUMIDITY	Humidity sensor	Measures the ambient relative humidity, in a percentage (%).	Monitoring the dew point, absolute humidity, and relative humidity
BAROMETER	Barometer sensor	Measures the barometric pressure, in the unit of hPa or mbar.	Measuring the barometric pressure
ORIENTATION	Orientation sensor	Measures the rotation angles of a device on three physical axes (X, Y, and Z), in the unit of rad.	Providing the three orientation angles of the screen
ROTATION_VECTOR	Rotation vector sensor	Measures the rotation vector of a device. It is a composite sensor that generates data from the acceleration sensor, magnetic field sensor, and gyroscope sensor.	Detecting the orientation of a device in the East, North, Up (ENU) Cartesian coordinate system
PROXIMITY	Proximity sensor	Measures the distance between a visible object and the device screen.	Measuring the distance between a person and the device during a call
AMBIENT_LIGHT	Ambient light sensor	Measures the ambient light intensity of a device, in the unit of lux.	Automatically adjusting the screen brightness and checking whether the screen is covered on the top
HEART_RATE	Heart rate sensor	Measures the heart rate of a user.	Providing users’ heart rate data
WEAR_DETECTION	Wear detection sensor	Checks whether a user is wearing a wearable device.	Detecting wearables
HALL	Hall effect sensor	Detects a magnetic field around a device.	Smart cover mode of the device

Working Principles

The following modules work cooperatively to implement OpenHarmony sensors: Sensor API, Sensor Framework, Sensor Service, and HDF layer.

Figure 1 How the sensor works

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Sensor API: provides APIs for performing basic operations on sensors, including querying the sensor list, subscribing to or unsubscribing from sensor data, and executing control commands. This module makes application development simpler.
Sensor Framework: manages sensor data subscription, creates and destroys data channels, subscribes to or unsubscribes from sensor data, and implements communication with the Sensor Service module.
Sensor Service: interacts with the HD_IDL module to receive, parse, and distribute data, manages foreground and background policies and sensors of a device, and controls sensor permissions.
HDF layer: selects proper policies based on the hardware first in first out (FIFO) and frequency, and adapts to different devices.

Constraints

To obtain data of the following sensors, you must request the required permissions.

Sensor	Permission	Sensitivity	Permission Description
Acceleration sensor, uncalibrated acceleration sensor, and linear acceleration sensor	ohos.permission.ACCELEROMETER	system_grant	The permission allows an application to read data from acceleration sensors, uncalibrated acceleration sensors, and linear acceleration sensors.
Gyroscope sensor and uncalibrated gyroscope sensor	ohos.permission.GYROSCOPE	system_grant	The permission allows an application to read data from gyroscope sensors and uncalibrated gyroscope sensors.
Pedometer sensor	ohos.permission.ACTIVITY_MOTION	user_grant	The permission allows an application to read an end user’s motion status, for example, to determine whether the user is in motion or to record the number of steps that the user has walked.
Heart rate sensor	ohos.permission.READ_HEALTH_DATA	user_grant	The permission allows an application to obtain an end user’s health data, such as heart rate data.

The APIs for subscribing to and unsubscribing from sensor data work in pairs. If you do not need sensor data, call the unsubscription API to stop sensor data reporting.