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介绍传感器
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.
Android sensor framework 让你使用多种传感器。有基于硬件和基于软件的。基于硬件的传感器是内置于设备中的物理组件。它们直接测量具体的环境属性来得出数据，例如加速度，地磁场强度，或者角的变化。基于软件的传感器你不是物理设备，尽管它们模拟硬件传感器。软件探测器通过一个或者多个硬件传感器来得出数据，有时称为虚拟传感器或者合成传感器。线性加速度传感器和重力传感器是软件传感器的例子。
Table 1 summarizes the sensors that are supported by the Android platform.
表1 总结了android 平台支持的传感器。
Few Android-powered devices have every type of sensor. For example, most handset devices and tablets have an accelerometer and a magnetometer, but fewer devices have barometers or thermometers. Also, a device can have more than one sensor of a given type. For example, a device can have two gravity sensors, each one having a different range.
少有android 设备每种传感器都有。例如，大部分手机设备和平板有一个加速计和一个磁力计，但是较少设备有气压计或温度计。一个设备也可以有一个以上的同类传感器，如果可以用两个不同范围的重力传感器。
Table 1. Sensor types supported by the Android platform.
表1。Android 平台支持的传感器种类。
| Sensor | Type | Description | Common Uses |
|---|---|---|---|
TYPE_ACCELEROMETER | Hardware | Measures the acceleration force inm/s2 that is applied to a device on all three physical axes (x, y, and z), including the force of gravity. 测量在设备的三个轴的加速度，单位 m/s2 ，包括重力加速度 | Motion detection (shake, tilt, etc.). 运动检测 |
TYPE_AMBIENT_TEMPERATURE | Hardware | Measures the ambient room temperature in degrees Celsius (°C). See note below. 测量室温，单位摄氏度(°C) | Monitoring air temperatures. 监视空气温度 |
TYPE_GRAVITY | Software or Hardware | Measures the force of gravity in m/s2 that is applied to a device on all three physical axes (x, y, z). 测量在设备三个轴的重力加速度，单位m/s2 。 | Motion detection (shake, tilt, etc.). |
TYPE_GYROSCOPE | Hardware | Measures a device's rate of rotation in rad/s around each of the three physical axes (x, y, and z). 测量在设备三个轴上的角速度。单位rad/s | Rotation detection (spin, turn, etc.). 旋转检测 |
TYPE_LIGHT | Hardware | Measures the ambient light level (illumination) in lx. 测试环境亮度级，单位 lx | Controlling screen brightness. 控制屏幕亮度 |
TYPE_LINEAR_ACCELERATION | Software or Hardware | 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. 测量在设备三轴上的加速度，排除了重力。 | Monitoring acceleration along a single axis. 检测一个轴上的加速度 |
TYPE_MAGNETIC_FIELD | Hardware | Measures the ambient geomagnetic field for all three physical axes (x, y, z) in μT. 测量三轴的地磁场，单位μT | Creating a compass. 创建一个罗盘 |
TYPE_ORIENTATION | Software | Measures degrees of rotation that a device makes around all three physical axes (x, y, z).As of API level 3 you can obtain the inclination matrix and rotation matrix for
a device by using the gravity sensor and the geomagnetic field sensor in conjunction with the 测量设备绕三轴转的旋转度。 | Determining device position. |
TYPE_PRESSURE | Hardware | Measures the ambient air pressure in hPa or mbar.测量气压 | Monitoring air pressure changes. |
TYPE_PROXIMITY | Hardware | Measures the proximity of an object in cm relative to the view screen of a device. This sensor is typically used to determine whether a handset is being held up to a person's ear. | Phone position during a call. |
TYPE_RELATIVE_HUMIDITY | Hardware | Measures the relative ambient humidity in percent (%). | Monitoring dewpoint, absolute, and relative humidity. |
TYPE_ROTATION_VECTOR | Software or Hardware | Measures the orientation of a device by providing the three elements of the device's rotation vector. | Motion detection and rotation detection. |
TYPE_TEMPERATURE | Hardware | Measures the temperature of the device in degrees Celsius (°C). This sensor
implementation varies across devices and
this sensor was replaced with the TYPE_AMBIENT_TEMPERATURE sensor in
API Level 14 | Monitoring temperatures. |
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