Sensors Overview:
Most Android-powered devices have built-in sensors that measure motion, orientation,
and various environmental conditions. These sensors are capable of providing raw data with high
precision and accuracy, and are useful if you want to monitor three-dimensional device movement or
positioning, or you want to monitor changes in the ambient environment near a device. For example, a
game might track readings from a device's gravity sensor to infer complex user gestures
and motions, such as tilt, shake, rotation, or swing. Likewise, a weather application might use a
device's temperature sensor and humidity sensor to calculate and report the dewpoint, or a travel
application might use the geomagnetic field sensor and accelerometer to report a compass
bearing.
The Android platform supports three broad categories of sensors:
- Motion sensors: These sensors measure acceleration forces and rotational forces along three axes. This category includes accelerometers, gravity sensors, gyroscopes, and rotational vector sensors.
- Environmental sensors: These sensors measure various environmental parameters, such as ambient air temperature and pressure, illumination, and humidity. This category includes barometers, photometers, and thermometers.
- Position sensors: These sensors measure the physical position of a device. This category includes orientation sensors and magnetometers.
You can access sensors available on the device and acquire raw sensor data by using the Android
sensor framework. The sensor framework provides several classes and interfaces that help you perform a wide
variety of sensor-related tasks. For example, you can use the sensor framework to do the following:
- Determine which sensors are available on a device.
- Determine an individual sensor's capabilities, such as its maximum range, manufacturer, power requirements, and resolution.
- Acquire raw sensor data and define the minimum rate at which you acquire sensor data.
- Register and unregister sensor event listeners that monitor sensor changes.
Introduction to Sensors:
The Android sensor framework lets you access many types of sensors. Some of these sensors are
hardware-based and some are software-based. Hardware-based sensors are physical components built
into a handset or tablet device. They derive their data by directly measuring specific environmental
properties, such as acceleration, geomagnetic field strength, or angular change. Software-based
sensors are not physical devices, although they mimic hardware-based sensors. Software-based sensors
derive their data from one or more of the hardware-based sensors and are sometimes called virtual
sensors or synthetic sensors. The linear acceleration sensor and the gravity sensor are examples of
software-based sensors.
Some Hardware based Sensors are described below:
-
Sensor.TYPE_GYROSCOPE
- Sensor.TYPE_MAGNETIC_FIELD
- Sensor.TYPE_ACCELEROMETER
Some Software based Sensors are described below:
- Sensor.TYPE_ORIENTATION
- Sensor.TYPE_GRAVITY: This comes in Hardware based Sensors too.
Sensor Framework:
You can access these sensors and acquire raw sensor data by using the Android sensor framework.
The sensor framework is part of the
android.hardware package and includes the following
classes and interfaces:
SensorManager:
- You can use this class to create an instance of the sensor service. This class provides various methods for accessing and listing sensors, registering and unregistering sensor event listeners, and acquiring orientation information. This class also provides several sensor constants that are used to report sensor accuracy, set data acquisition rates, and calibrate sensors.
Sensor:
- You can use this class to create an instance of a specific sensor. This class provides various methods that let you determine a sensor's capabilities.
SensorEvent:
- The system uses this class to create a sensor event object, which provides information about a sensor event. A sensor event object includes the following information: the raw sensor data, the type of sensor that generated the event, the accuracy of the data, and the timestamp for the event.
SensorEventListners:
- You can use this interface to create two callback methods that receive notifications (sensor events) when sensor values change or when sensor accuracy changes.
In a typical application you use these sensor-related APIs to perform two basic tasks:
- Identifying sensors and sensor capabilities
Identifying sensors and sensor capabilities at runtime is useful if your application has features that rely on specific sensor types or capabilities. For example, you may want to identify all of the sensors that are present on a device and disable any application features that rely on sensors that are not present. Likewise, you may want to identify all of the sensors of a given type so you can choose the sensor implementation that has the optimum performance for your application.
- Monitor sensor events
Monitoring sensor events is how you acquire raw sensor data. A sensor event occurs every time a sensor detects a change in the parameters it is measuring. A sensor event provides you with four pieces of information: the name of the sensor that triggered the event, the timestamp for the event, the accuracy of the event, and the raw sensor data that triggered the event.
Sensor Availability:
While sensor availability varies from device to device, it can also vary between Android
versions. This is because the Android sensors have been introduced over the course of several
platform releases. For example, many sensors were introduced in Android 1.5 (API Level 3), but some
were not implemented and were not available for use until Android 2.3 (API Level 9). Likewise,
several sensors were introduced in Android 2.3 (API Level 9) and Android 4.0 (API Level 14). Two
sensors have been deprecated and replaced by newer, better sensors.
