GMAT9205 – Geopositioning Lecturer : Dr Jinling Wang RTK vs SPP Student: Boata IABETA (z ) SCHOOL OF SURVEYING & SPATIAL INFORMATION SYSTEMS

Outline: 1.RTK GPS technique 2.Performance of RTK 3.Suitability of RTK 4.Application 5.SPP 6.Conclusion

“Carrier phase based” relative positioning Employs 2 receivers or more - simultaneously tracked the same satellites (at least 4) 1 receiver as Base station – remain stationary over known point, radio transmitter, Another receiver over unknown point Position of unknown point – built-in software in receiver. RTK GPS technique…..

RTK performance… It is different from Conventional DGPS in 3 majors aspects; 1. Typically accuracy – “hundreds times as good as DGPS” 2. Initialization period – “ There is an initialization following power on. The initialization calculates the integer number of carrier phase measurement – known as fixing integer” 3. There is no-zero probability that the initialization will be wrong source: Frank (1997)

RTK performance… source: Frank (1997) 1 - Single frequency receiver 2-Dual frequency receiver

RTK performance… source: Frank (1997) 1 - Single frequency receiver 2-Dual frequency receiver

RTK performance… ACCURACY – “ Once the integers are fixed correctly, RTK accuracy is at the centimetre-level.” “During the integer fixing phase, while the integers are being fixed they are modelled as real numbers (or floating-point numbers), and the position is referred to as ‘float’ solution.” source: Frank (1997)

RTK-GPS suitable….  Survey involves a large number of unknown points located in the vicinity of the known points  The coordinates of the unknown points are required in real time  Line of sight, the propagation path is relatively unobstructed. source: El-Rabbany (2002)

RTK application. MONITORING THE STABILITY AND DISPLACEMENT OF TV Tower (Stuttgard, Germany)  GPS UNIT ATTACHED TO THE TV TOWER (155m above ground level)  REFERENCE STATION - 450m (away from the structure)  MEASUREMENT – commences for a (duration of 2mins) source: Breneur et al (2002)

RTK application Result : 2min measurements with wind velocity of 7m/s - elliptical movement - cross-wind displacement - approx 4cm - along wind displacement - 2.5cm

SPP technique…. Standalone or autonomous positioning Involves one GPS receivers Based on “pseudo-range measurement” Receiver position based on the satellites coordinates as well as a minimum of 4 ranges to four satellites are required.

Conclusion… Both GPS system – produce the position of unknown right in the field – that is in real time with no post- processing is required. RTK provide quality data – cm level, more accurate GPS technique than SPP technique. References: -Breneur P & Chmielewski T & Gorski P & Konopka E, 2002 “ Application of GPS technology to measurements of displacement of high-rise structure due to weak winds” Elsevier Science, Germany -El-Rabbany, A. 2002, “ Introduction to GPS – The Global Positioning System” Artech House, USA -Frank. V D, 1997 “ GPS and GPS+GLONASS RTK” Ashtech Inc. Sunnyvale, California, USA

RTK result….

SPP result….