Real-time GNSS Positioning: Evolution, Practical Applications and Perspectives for the Future
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Abstract
Real-time positioning using satellite signals was an advance for air, sea and land navigation with the arise of GPS (Global Positioning System). However, the achievable horizontal and vertical accuracy of 100 m and 150 m (95% probability level), when SA (Selective Availability) technique was activated, became unsatisfactory for many applications and users required other accuracy levels. Efforts were dedicated to the so-called differential positioning, DGPS (Differential GPS), which made it possible to achieve precision about ten times better than that usually obtained throughout absolute positioning. Later, using carrier-phase measurements, it was possible to perform positioning with greater accuracy through the RTK (Real Time Kinematic) method, reaching centimeter quality. Subsequently, there was an evolution towards network-based positioning, using, for example, the VRS (Virtual Reference Station) algorithm. Several errors affecting satellite observables started to be modeled in real time with multi-station solutions. As of 2012, services and products were developed in order to accomplish RT-PPP (Real-Time Precise Point Positioning), a method based on the SSR (State Space Representation) concept. Further, the ambiguity fixing in RT-PPP became possible, and this approach is usually referred as PPP-RTK, which provides a faster convergence to an accurate positioning solution. This article presents the evolution real time positioning, some applications at the national context, as well as the future perspectives.
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