sensor-overview.md

# Sensor Overview


Sensors in OpenHarmony are an abstraction of underlying sensor hardware. Your application can access the underlying sensor hardware via the sensors. Using the [Sensor](../reference/apis/js-apis-sensor.md) 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/s<sup>2</sup>.| 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/s<sup>2</sup>.| 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/s<sup>2</sup>.| 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/s<sup>2</sup>.| 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

![fad1a124-a90e-460f-84fc-e87d6caebb21](figures/fad1a124-a90e-460f-84fc-e87d6caebb21.png)

- 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

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

    | Sensor                      | Permission                             | Sensitivity        | Permission Description                   |
    | ------------------------- | -------------------------------- | ------------ | ----------------------- |
    | Acceleration sensor, uncalibrated acceleration sensor, and linear acceleration sensor| ohos.permission.ACCELEROMETER    | system_grant | Allows an application to subscribe to data of these acceleration-related sensors in the motion category.|
    | Gyroscope sensor and uncalibrated gyroscope sensor         | ohos.permission.GYROSCOPE        | system_grant | Allows an application to subscribe to data of the gyroscope-related sensors in the motion category.|
    | Pedometer sensor                      | ohos.permission.ACTIVITY_MOTION  | user_grant   | Allows an application to subscribe to the motion status.               |
    | Heart rate sensor                      | ohos.permission.READ_HEALTH_DATA | user_grant   | Allows an application to read health data.               |
    
2. 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.