Mobile GPS data processing

　　The collection process of GPS data will be affected by many external factors, which will lead to errors in the quality of GPS data. The causes of these errors are mostly unavoidable, so the impact on mobile GPS data is unavoidable. Therefore, mobile GPS data cannot be directly used to estimate and forecast traffic flow. Otherwise, if the data with large error is directly used to estimate the average speed of traffic flow, the accuracy of estimation will be greatly affected due to error transmission. In order to reduce the adverse effects of data errors, the original data should be processed first.

　　The original data can be divided into two types according to the degree of impact: one is data with small deviation, and the other is data with errors. Different measures should be taken to preprocess different data. Wrong data should be eliminated; The data with slight deviation should be corrected to ensure that the data can be projected onto a reasonable road network. Error data is usually caused by serious interference of GPS satellite signals during transmission, such as sudden changes in relatively dense large buildings, dense forest trees or electromagnetic waves, which make the positioning data seriously deviate from the historical track. Because this kind of data can hardly reflect the driving situation of the vehicle, it can not represent the correct position of the vehicle and needs to be deleted from the original data. For such errors, the threshold test method is usually used to judge. This method assumes that the reasonable value of vehicle speed is a fixed range. When a certain speed exceeds this reasonable range, it means that the data is incorrect and needs to be eliminated. The deviation data is usually caused by GPS positioning error, which often happens, and such data should be considered as normal data. This kind of data also needs to be modified, and the usual method is the algorithm of electronic map matching [4,5]. This method projects the mobile GPS data on the map, and makes a vertical line to the matching road section according to the projected data points, so the intersection point with the matching road section is the matching position of the data point

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