5 minutes to receive data about satellite constellation. By employing the A-GPS, Vandetanib the first fix is provided within few seconds. Additionally, a GSM modem can support a GPS receiver with a rough location which is obtained by measuring the strengths of signals from GSM base stations.Apart from L1 = 1,227 MHz, a second frequency called L2C = 1,575 MHz, has been made available to the civilian sector with the aim of reducing the ionospheric and tropospheric errors which are a well defined function of frequency. Also, the so-called augmentation systems effectively reduce tropospheric and ionospheric errors by sending differential corrections from geostationary satellites directly to GPS receivers. The geostationary satellites imitate also GPS satellites and improve mainly the vertical accuracy.
EGNOS (European Geostationary Navigation Overlay Service) works in Europe, WAAS (Wide Area Augmentation System) in the US, MSAS (Multi-functional Satellite Augmentation System) in Japan and GAGAN (GPS aided Geo-Augmented Navigation) in India.Real Time Kinematics technique achieves the accuracy of millimetres in an open space and is designated for cartographic measurements. However, two GPS receiver are necessary. The base receiver is placed in a known position and calculates tropospheric, ionospheric, ephemerids and clock errors of satellites. The corrections are sent via a radio link to a mobile GPS receiver. In the trials reported in [4] RMS error of 2 cm on a mountain high-way was noted whereas trials in urban canyons yielded a 50 m RMS error.
All the above mentioned Dacomitinib techniques are helpless against multipath propagation errors. Algorithms harnessed in car navigation alleviate these errors by taking advantage of car kinematics and a comparatively sparse network of roads, as described, e.g., in [7] or [8]. An error of 20 m is of no bigger importance to a driver. In case of navigating pedestrians, especially blind ones, the target accuracy should ideally not exceed the pavement width, i.e., ca. 2 m.This work presents a navigation scheme using GPS readouts, digital maps, inertial sensors and stereovision images with an aim of navigating a blind pedestrian. An accelerometer is used to detect pedestrian’s strides and estimate their length. A gyroscope serves for estimating the heading direction. Those data sources help eliminate gross positioning errors and outliers.
The digital maps are used twofold. Firstly, the so-called probability map is built to eliminate improbable user transitions, like traversing the water ponds, crossing walls and buildings, etc. Secondly, a 3D model of the environment is built. The model is compared to stereoscopic images recorded by a mobile stereo camera. Interestingly, this comparison of 3D geometry of the environment provides good positioning accuracy in the surrounding of buildings, where GPS readouts are compromised.