GPS solutions for roads. Different GPS operation types and applications

Transcription

1 GPS solutions for roads. Different GPS operation types and applications NICOLAE ION BĂBUCĂ Department of Land Measurements and Cadastre POLITEHNICA University of Timisoara Timisoara, P-ta Victoriei no. 2 ROMANIA cristi.babuca@gmail.com Abstract: - All GPS Surveying is carried out using differential techniques. That is to say a baseline is measured from a fixed point, (a reference station) to an unknown point (a rover station). The surveyor should choose the appropriate technique for the application. Static - Used for long lines, geodetic networks, tectonic plate studies etc. Offers high accuracy over long distances but is comparatively slow. Rapid Static - Used for establishing local control networks, Network densification etc. Offers high accuracy on baselines up to about 20km and is much faster than the Static technique. This is undertaken using one of two methods : PostProcessing The raw GPS data from the satellites is recorded and processed in the office using software RealTime The processing of the data is carried out as you work, giving an instantaneous and accurate position Key- Different GPS Operation Types and Applications 1. Introduction Using GPS for Surveying Static Rapid Static Static Survey The classical method for long lines and the highest accuracy 3mm + 1ppm baseline rms Classical GPS baseline measurement, where each line is observed for at least two hours The observation time is proportional to the length of the line Standard method for lines over 20 Km Applications Geodetic control over large areas National and continental networks Monitoring tectonic movement Network adjustments for highest accuracy Rapid Static Survey (STS) Short observation time for baselines up to 20 km. Accuracy is 5-10 mm + 1 ppm Applications Control Surveys, GIS city inventories, detail surveys. Replace traversing and local triangulation. Any job where many points have to be surveyed Advantages Easy, quick, efficient Ideal for short range survey Fig.1, Rapid Static ISBN:

2 2. GPS Measurements Soultions for determining the transformation parameters In order to determine the transformation parameters from WGS 1984 to Stereographic 1970 for the work area, GPS STATIC method measurements have been conducted using national geodetic network 1 st rank points. After conducting GPS measurements on national geodetic points, 6 points were used for the transformation parameters: CALACEA, TISA NOUĂ, VARIAŞU MARE, CURTICI, MOŞNIŢA and DEALUL PĂZIT. Semlac point was eliminated, because there were differences in height. Fig.2, GPS Network also as starting point for the network processing), CALACEA, TISA NOUĂ and DEALUL PĂZIT. During all sessions, the four points were occupied simultaneously with 4 Leica GPS1200 receivers, the standing time being minimum 5 hours, except for Tisa Nouă point (for which the first session was of 2h and 25 minutes) and for Mosniţa point (for which the second session was of 3h and 5 minutes). Second polygon: CALACEA, TISA NOUĂ, VARIAŞU MARE and CURTICI. The points were simultaneously occupied, same as for the first polygon, with 4 Leica GPS1200 receivers, the standing time being 5 hours for each point, for both sessions, without exception Tabel 1, Transformation parameters Ellipsoid A WGS 1984 ELLIPSOID Krassowski B Height Mode Orthometric Model Bursa Wolf Dx 102,4110 Dy -281,5579 Dz 103,5538 Rx 8,48984 Ry 1,99565 Rz -10,74588 Scale factor -0,465 The collected data were processed using LEICA GEO OFFICE v. 3.0 software, thus obtaining the transformation parameters for the entire polygon. No. ID Northing (m) Easting (m) Height (m) 1 Moşnita Calacea Tisa Noua 4 Dealul Păzit 6 Variaşu Mare 7 Curtici Height system: Black Sea Coordinate system: Stereographic 1970 Two polygons were formed from these points, and three measurement sessions were conducted for each polygon, in three different days. The polygons have CALACEA TISA NOUĂ as common starting point. First polygon: MOŞNIŢA (point EUREF, which has well established coordinates, set as control point and ISBN:

3 3. Benchmark placement After an on site reconnaissance, the positions for the benchmark placement were identified taking into consideration all the conditions provided in Methodology topographical works (the absence of magnetic fields or reflecting surfaces, the absence of obstacles in order to receive the signal starting at a minimum height of 20 o cut angle, the benchmarks were placed at cadastral limits etc.). Type A BENCHMARK : A2 Type B BENCHMARK : B5 4. Survey for the main and secondary polygonal benchmarks The surveys for the main (type A) and secondary (type B) polygonal benchmarks were carried out by STATIC GPS method therefore type A and type B benchmarks have the same accuracy occupying 6 points 3 points simultaneously from the main STEREO 70 network, and 3 benchmarks (type A or B). The surveys were carried out using 5 Leica GPS 1200 and one Leica Smartstation with Raw Data Logging capability enabled. For determining secondary points, two GPS measurements sessions were conducted. ISBN:

4 The first session started at 9:50 with reference stations on points Calacea, Variaşu Mare şi Tisa Nouă and rovers on points A1, A2, A3, A4, A5, and points B1, B2, B3, B4, B5, B6 respectively. Standing times: points A1-A5 were surveyed for 2 hours. s B1-B6 were surveyed for 1 hour and 30 minutes. The second session started at 7:55 with reference stations on the same points and with the same standing times for the new points. A 1 st rank levelling benchmark was surveyed, in order to check the height and have control over the height. After the data processing, using Leica Geo Office v software, the coordinates of the 5 Type A and 6 Type B benchmarks were calculated and compensated (Leica Geo Office, "Network Adjustment"). Compensated Coordinates: Northing Easting Height ID. A reference station. The distance can be extended by using mobile phone systems for transmitting the mentioned corrections via Internet. The deriving issue regards the fact that both the fixed station that transmits the corrections, and the mobile station need to acquire signals from a minimum of four satellites. Therefore, the distance between the two receivers cannot be greatly increased. The main causes of GPS measurement errors are: Errors concerning time estimates for GPS data propagation; Errors related to information transmitted via satellite, regarding satellite clock and orbital data; Voluntary errors, caused by voluntary damaging of the GPS system; All these errors are correlated for the entire area of interest and they are correlated by this radio data transmittal differential system. A A A A B B B B B B Radio Wave RTK (real-time) Method 5.1 Principle The principle of differential GPS system consists of observing pseudo-distances measurement errors by following every visible satellite from a reference point with an accurately known position in WGS 84 (World Geodetic System). Observing this errors allows the determination of the corrections, which are transmitted by radio, so that users (mobile stations) working in the area of interest around the reference station. The most competitive radio transmitting systems for corrections nowadays allow for these corrections to be transmitted up to a distance of km from the Fig. 3, Data transmittal via radio waves 5.2 Calculating the corrections provided by the reference station and their reception at the mobile station The corrections are calculated by a receiving module, equipped with 12/16 parallel reception channels, allowing the simultaneous computation of corrections from 12/16 satellites. For each satellite, the reception module calculates: The difference between the measured distance and the theoretical distance derived from the ephemeride data and from the known position of the reference station's GPS antenna; ISBN:

5 The correction evolution's velocity; Corrections are computed every 0.6 seconds for all satellites and are transmitted to the central unit that manages the transmission. A correction message transmitted to the central unit by the GPS receiver module comprises: The week number; The Z Counter, which allows for precision dating of every correction on the GPS timescale; An indication of ephemeride change; The observed correction; The correction evolution velocity; The satellite number; The ionospheric correction calculated at the reference station; The tropospheric correction calculated at the reference station; Conclusions With a new, ultra-precise GPS measurement engine, new, fast, self-checking RTK algorithmsand a comprehensive, self-explanatory user interface, LEICA System 1200 receivers provideall the flexibility, power and performance needed for every type of GPS application. Built to the toughest MIL specifications, they withstand extreme temperatures, the worst weather and the roughest site conditions. References [ 1 ] Neuner, J., Sisteme de pozitionare globala, MatrixRom Publishing House, Bucharest, 2000; [ 2 ] Grecea, C., Introducere în geodezia satelitară, Mirton Publishing House, Timişoara 1999; [ 3 ] Boş, Nicolae & Iacobescu, Ovidiu, Topografie modernă, C.H. Beck Publishing House, Bucharest, 2007; [ 4 ] ***Colectiv Cadastru, UP Timisoara, Complemente de Masuratori Terestre, Politehnica Publishing House, 2006 *** ISBN: