engleski

Testing the accuracy of Locata positioning system for the purpose of determination the static and dynamic displacement measurements

GNSS has limitations or cannot be applied in specific environments with poor geometry like city streets, tunnels, bridges, or in indoor environment in general. To overcome these difficulties many researches have supplemented GNSS with pseudolites which also have their own limitations. Locata Corporation from Australia developed new radio-frequency based positioning system called Locata which relies on the network of ground-based, time synchronized transceivers (LocataLites) that transmit positioning signals on 2.4 GHz frequency (wavelength approximately 12 cm). Biggest achievement of Locata positioning system is new, patented, wireless technology for time synchronization between LocataLites, called TimeLoc. Capability of Locata positioning system for displacement measurement was briefly tested on a few occasions, e.g. displacement measurements of footbridge at Parsley Bay in Sydney and slow structural deformation monitoring at Tumut Pond Dam. Within the project “Wearable outdoor augmented reality system for enrichment of touristic content”, code-named “Project Wonderland”, Locata positioning system was implemented in the City of Čakovec, Croatia at Polytechnic’s of Međimurje backyard. Installed Locata equipment consists of six LocataLite transceivers with 18 itelite PAT24009 antennas (three antennas for each LocataLite) and two Locata receivers with two L-Com HG2403MGU-SM antennas. Prior to establishing Locata network (LocataNet) in the field, different network configurations were simulated to achieve best possible horizontal and vertical positioning accuracy. The main task was to find optimal network configuration for getting acceptable accuracy of vertical component of positioning solution (i.e. to get the lowest possible values of vertical dilution of precision). As optimal configuration, rectangular shape of 100 meters times 50 meters was chosen and established in the field. Geodetic control network was established around Locata network by classical measurements obtained by Leica TPS1201 robotic total station. Coordinates of control network were determined with the accuracy better than 2 millimeters in horizontal and vertical direction. Control network was used as a reference for determining coordinates of LocataLite antennas. In established LocataNet, measurements were conducted and analyzed to get insight into the precision and accuracy of absolute and relative positioning techniques. Analysis of obtained measurements shows precision of sub-centimeter level in horizontal direction and precision of two-centimeter level in vertical direction in terms of absolute positioning. Achieved accuracy was within 2 centimeter in horizontal direction and 3-5 centimeters in vertical direction. Using relative positioning technique significant noise reduction was accomplished, with achieved precision within few millimeters in horizontal, and up to 1 cm in vertical direction The goal of this research is to get the insight into the possibilities of the Locata positioning system to determine both long term (static) and short term (dynamic) displacements of constructions. Future research will include establishment of new Locata network in Zagreb with more extensive research on positioning using Locata, as well as research on different components that affects positioning solution (e.g. different ambiguity resolution techniques, modeling antenna phase center offset and variations, using double differenced signals for relative positioning…). Final goal of research is to establish Locata network around railway bridge Sava in Zagreb for long and short term displacement measurements. The behavior of that bridge under static and dynamic load testing is known from previously accomplished measurements and conducted results.

Locata, LocataNet, displacements, testing of precision and accuracy

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