Performance Analysis of PPP Technique Using GPS-only and GPS+GLONASS in Urban Environment Reha Metin ALKAN 1, 2 , Veli İLÇİ 1 & İ. Murat OZULU 1 Presented by: R.M. ALKAN 1 Hitit University- Çorum/TÜRKİYE 2 Istanbul Technical University- Istanbul/TÜRKİYE September 1-3, 2014 / Alexandria, Egypt Melaha 2014
Overview Motivation Introduction Experiments & Data Processing And Analysis Evaluation of the Measurements Conclusion Melaha 2014
Motivation The primary motivation of this study is; to compare the PPP results using GPS-only and the combined GPS+GLONASS data by using the Canadian Spatial Reference System-Precise Point Positioning, CSRS-PPP online-PPP service. Melaha 2014
Introduction Precise Point Positioning (PPP) is an absolute positioning technique that has been increasingly used in recent years. In this method, the positioning can be realized within a decimeter to centimeter level of accuracy within a global reference frame, ITRF, with ease economically, and, without any need of a base station. Melaha 2014
Precise Point Positioning (PPP) This technique utilizes precise satellite orbits and clocks information (supported by different organizations such as IGS, CODE, JPL), un-differenced code pseudoranges and/or carrier phase observations. Melaha 2014
All those factors have forced users to use the method all around the world and also many academics have begun to show interest during the past two decades. Currently, the Global Positioning System (GPS) is the preferred tool all over the world for both geodetic applications and PPP studies, which are mostly processed using GPS observations. Melaha 2014
In some environments such as urban canyons, areas with heavy tree cover, mountains, ravines and open-pit mines, the availability and reliability of positioning accuracy is affected by an insufficient number of visible satellites. Melaha 2014
Insomuch as poor satellite geometry may deteriorate the positional accuracy of PPP in open areas. Melaha 2014
Taking into account all of these weaknesses of GPS, researchers are focused on the integration of GPS and other GNSS system like the Russian Global Navigation Satellite System, GLONASS, observations to increase both the accuracy and reliability of PPP results for all areas. Melaha 2014
GLONASS began development in the year 1976, and achieved full operational capability in 1996. In 2000, after a period of economic recession, GLONASS started to be reconstructed by the Russian government. In 2011, the full orbital constellation of 24 satellites was restored and it has since reached full global coverage. Melaha 2014
As of today, totaly about 60 satellites can be used by combining the GPS and GLONASS system. This can provide better performance with more satellites in view. The use of both GPS and GLONASS together, against that of GPS alone, improve both precision and accuracy. Melaha 2014
In general, the satellites that are usually available for use are 8 to 12 for GPS and 6 to 10 for GLONASS. When GPS and GLONASS satellites are used together, this number can reach up to 14 to 20 satellites. Melaha 2014
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On-line Processing Services There are several ways to obtain coordinates in PPP mode; - in-house software - scientific processing packet softwares: Bernese, Gipsy, WaPPP, P3, … - web-based online processing services: CSRS-PPP, GAPS, APPS, magicGNSS, … Melaha 2014
The common way to obtain PPP-derived coordinates is to use an on-line processing service. Nowadays, several web- based on-line processing services are available for free of charge or with a very limited license fee. Melaha 2014
Users do not need to know GPS processing software or have a deep knowledge of GNSS. Because of these advantages, the usability of an on-line processing service like CSRS-PPP has become more popular and the number of user have increased very rapidly all over the world. Melaha 2014
The major drawback of the web services are that the systems do n’t allow users to select the available options rather than the optimal options set by the system. Melaha 2014
Online services provide PPP-derived coordinates easily and cost-effectively without using a GPS software directly. Melaha 2014
In this study, the CSRS-PPP on-line processing service was used to obtain the estimated PPP-derived coordinates. Canadian Spatial Reference System-Precise Point Positioning - CSRS-PPP: The service may estimate single station positioning in both static and kinematic mode and it uses precise GPS orbit and clock products provided by IGS and Natural Resources Canada (NRCan). CSRS are capable of computing from carrier phase/code pseudorange observations of both single and dual frequency receivers. Melaha 2014
Canadian Spatial Reference System-Precise Point Positioning (CSRS-PPP) The service includes an option for users to select datum in results. Moreover, the solutions of PPP coordinates are sent in both NAD83 and ITRF datums with detailed graphical analysis reports. To have free access to the service, the user should take a user name and a password from the site for membership. Melaha 2014
Experiments & Evaluation In order to examine the feasibility of the PPP technique combining both the GPS and GLONASS data, two static test measurements were conducted in Çorum , Turkey on February 21 and February 26, 2014. Melaha 2014
18 geodetic points were established for test measurements in the highly urban environment of Çorum City. The GPS and GLONASS data were collected about 1 hour data span at 1 second interval and the elevation cut-off angle was set to 10 ° . In this study, Spectra Precision EPOCH 50 dual-frequency GNSS receiver was used. Melaha 2014
All collected GPS data were converted into the RINEX format and uploaded to the web-based online services by choosing appropriate selections and estimated PPP-derived coordinates were obtained. Melaha 2014
To obtain reference coordinates; two of the Turkish RTK CORS Network points were used as reference stations to obtain highly accurate known coordinates of the established 18 points with a differential technique. Melaha 2014
The GPS-only and GPS+GLONASS coordinates derived from online-PPP service were compared with those of the differential technique results. The differences in both position and ellipsoidal height are shown in the following Figures. Melaha 2014
Evaluation Results Differences between differential solution and CSRS-PPP (position) Melaha 2014
Differences between differential solution and CSRS-PPP (height) Melaha 2014
Number of satellites observed at stations Melaha 2014
Conclusion In this study, a comparison between GPS-only and GPS+GLONASS Precise Point Positioning in terms of accuracy were carried out. For this purpose, two different static trails were conducted in a highly urban area in Çorum City, Turkey. Melaha 2014
Conclusion Concerning the position accuracy issue, the GPS-only solutions produce nearly the same results, being within a 1 cm level, with the GPS+GLONASS solution being used for most of the points. In general, the PPP-derived coordinates can be obtained within a sub-decimeter level of accuracy for both a GPS-only and GPS+GLONASS solution, in an urban area by using on- line precession technique. Melaha 2014
Conclusion For the height components, the accuracy of the GPS+GLONASS PPP solution was found to be better than the GPS-only solution. The results show that, the GPS-only solution agreed with the relative positioning solution at the two decimeters level of accuracy in height components, while the GPS+GLONASS solutions had a decimeter level of accuracy with an improved accuracy. In general, the accuracy for height components can be improved by the use of an additional GLONASS constellation in most case. Melaha 2014
Conclusion The results show that using an additional GNSS system, the GLONASS constellation, help improve the number of available satellites (also measurements) by more than about 75% (in average) in comparison to the GPS constellation system. Melaha 2014
Conclusion The overall results show that, in general, an additional GNSS constellation allows for more reliable and precise surveying, especially in urban areas, areas with heavy tree cover, ravines, mountains, open pit mines and, in general, when the satellite signals are blocked or degraded by various obstacles. Melaha 2014
Thank you very much for your interest and attention… Contributions, Questions??? Dr. Reha Metin ALKAN Hitit University, Corum, Turkey & Istanbul Technical University (ITU) Geomatics Engineering Department, Istanbul, Turkey alkan@hitit.edu.tr alkanr@itu.edu.tr Melaha 2014
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