VALIDATION OF REAL-TIME PRECISION POSITIONING USING INEXPENSIVE SINGLE-FREQUENCY TYPE LOCAL-AREA RTK SYSTEM AND NETWORKS

We constructed a low-cost and easy-to-handle local-area RTK-GNSS positioning system which can automatically perform RTK positioning every second. The positioning was conducted at two reference stations to evaluate the accuracy and reliability of the real-time data: (1) at the university campus (ground fixed point) with obstacles such as buildings and trees, hindering a GNSS satellite signal reception and (2) at the open-sky rooftop of a 11-story school building (rooftop fixed point), where the reference station had been set up with only few obstacles to GNSS satellite signal reception. At the ground station, the network connection status, temperature, and relative humidity were also simultaneously measured. Consequently, 600 data were acquired in 10 min, and the data with the highest ratio were further selected for analysis. For the ground-based fixed points, the standard errors of all the data were >10 times more accurate than those of D-GNSS; however, such result is unsatisfactory, as previously anticipated for RTK positioning. We further filtered the data with less than 15 satellites and less than 9 ratio values and found that the data quality and reliability were improved to a satisfactory level. For the rooftop fixed point, the standard error of all the data was approximately 1 mm in both horizontal and vertical directions, thereby indicating higher accuracy than the data from the ground fixed point. Consequently, we obtained accurate and reliable data with less scatter. Overall, it is possible to obtain accurate and reliable RTK positioning data in real time using statistical processing to eliminate outliers.