infrastructure-independent navigation
1.1 By sensing Devices
1.1.1 catalog of device: smart phones, smart watches, smart glasses
1.1.2 they are equipped with a range of sensors:
*inertial and magnetic sensors
用于测量加速度、倾斜、冲击、震动、旋转和自由度（Dof）
行人航位推算（PDR）：步长、步数和方向进行定位方法。
periodicity, similarity and continuity of the step also can be incoorporate into the navigation estimation.
landmark :
accelaration landmarks; orientation landmark; pressure landmarks; visual landmark; audio landmarks and magnetic landmarks.
*cameras
visual odometry(视觉里程表): a local motion estimation method.
simultaneous localization and mapping(SLAM): feature correspondences are typically used to construct a map of the environment and estimate the pose of the camera with repect to the map.
suffer from drift of position estimates.
other sensor: barometers, microphone, light sensor
1.2 By learning and Sharing Knowledge
background: Leaning any reasonably large and complex environment is a time-consuming process.