Experimental evaluation of OmniSTAR VBS&HP-positioning in Kiev

Authors: NAU, "GRANAS" Ltd, KhNURE, MAO



The results of experimental estimation of accuracy and reliability of positioning in static and kinematic modes by use of differential VBS&HP -corrections of OmniSTAR BV company (Netherlands) are given in the report. Main principles and characteristics of VBS&HP -technologies and services of OmniSTAR BV (providing high precision differential DGPS navigation, geodetic survey and positioning support of GIS on a worldwide scale with a level of accuracy of ~1 m ( VBS ) and ~10 cm ( HP ) in real time are briefly described.

Such experimental researches are carried out in Ukraine for the first time, and their results, in opinion of authors, can represent considerable interest for several groups of GPS-users of Ukraine for which it is important not only high accuracy of positioning but also high efficiency of geodetic surveying and other precision works.

The experiments have been executed in Kiev on May, 24-26, 2006 on the territory of National Aviation University (NAU) and on the highway "Kiev - Zhitomir". For measuring and demonstrations of possibilities of OmniSTAR BV services of precision positioning on inquiry of "GRANAS" Ltd. has kindly given an easy access to VBS/HP -corrections for the specified period of time. The employees of National Aviation University (NAU), "GRANAS" Ltd., Kharkov National University of Radio Electronics (KhNURE), Main Astronomical Observatory of National Academy of Sciences of Ukraine and the interested geodetic organizations of Kiev took direct part in works. In the course of the experiments it was used special GPS equipment of NovAtel ProPak-LB Plus , capable to accept and process high precision VBS - and HP -corrections, geodetic receiver NovAtel DL-4 4 (as a base station), GPS receiver FlexPak-SSII (additional rover receiver), the complete set of geodetic GPS equipment Trimble 5700 and the software of post session processing of Trimble (USA) and NovAtel/Waypoint Consulting (Canada) companies.

Testing of characteristics of VBS&HP - positioning technologies was carried out in three stages:

  • On May, 24, 2006 – stage 1 - a stage of static observations on the roof of educational case of NAU ( session №1 );
  • On May, 25, 2006 - stage 2 - a stage of testing in a mode "stop&go" with static initialization on 20 reference points tied beforehand by the geodetic organization on the territory of NAU sessions №2 and №3 );
  • On May, 26, 2006 – stage 3 - - a stage of testing in a kinematic mode (with static initialization) of measurements onboard the automobile on the territory of Kiev and out of town sessions №4 and №5 );

As a result of processing and the analysis of the data it is shown, that the stated characteristics of accuracy are achieved in normal conditions of radio visibility of GPS satellites (at admissible geometry of working constellation) and geostationary satellites through which the correction information is delivered. At the same time, it is noted considerable (tens minutes) duration of the period of re-initialization for high precision HP mode after loss of tracking the geostationary satellites signals or by short term dilution of geometrical conditions in conditions of shading or high dynamics) of motions.

In the process of initialization a stand-alone mode of positioning solution with accuracy of several meters switches on. In some minutes the differential VBS -mode switches on – the receiver determines coordinates with accuracy of 1-2 m with subsequent smooth increase of accuracy. Then, in 5-10 minutes HP mode switches on and the errors of positioning (latitude, longitude, height) increase by jump with subsequent exponential decrease up to decimeter (~30 minutes for the achievement of the stated accuracy of determination of latitude and height are required, and ~ (60-120) minutes for longitude are required) and even sub-decimeter level. It is not managed to carry out the initialization in a kinematic mode on the territory of NAU and in a kinematic mode of measurements in the process of motions onboard the car.

On failure of tracking (absence of corrections, losses of tracking the satellites because of obstructions, sudden geometrical dilution of precision) the receiver by renewal of tracking passes to VBS mode (meter accuracy) and repeats a new initialization. It is noted considerable (tens minutes) duration of the period of re-initialization for precision HP mode after loss of tracking the signals of geostationary satellites or by short time dilution of geometry of working constellation of GPS satellites in conditions of shading or high dynamics of motions. Under very short breaks of receiving of corrections quick restoration of HP -operating mode without loss of accuracy was observed. In VBS mode sub-meter accuracy of positioning is provided rather reliably with rather short period of re-initialization even in a kinematic operating mode (in motion).

As a whole, the results of the experimental estimation of characteristics of accuracy and reliability of positioning, despite rather short period of testing (three days), correspond to the estimations of both OmniSTAR BV company, and to the estimations received by the independent organizations.

The stated decimeter accuracy of positioning in real time is also achievable, in principle, in conditions of town, but under conditions of reliable radio visibility of satellites, under « the open sky ». In conditions of high buildings (city "canyons"), constructions, trees surrounding a significant part of time the receiver makes often breaks of tracking, especially regarding on "low" GPS satellites. This also concerns the radio visibility of geostationary satellites through which differential corrections are transmitted.

The problem of a small number of visible satellites and bad GDOP is rather actual in conditions of modern cities. Obviously, it is possible to leave this in multi-system (GPS+ГЛОНАСС+Galileo) receivers or by integration with inertial systems or with other sources of the navigation information In Kiev during the experiments these problems have proved to be true. Therefore the achievement of decimeter accuracy in these conditions is possible with unsatisfactory probability. For a number of tasks which are solved in conditions of the open sky (cadastre survey, land surveying on the open district, GIS, hydrographic survey, aerophotogrammetry etc.) the use of high precision technologies OmniSTAR can be recognized as expedient and effective. But for final conclusions it is necessary to carry out the additional series of measurements onboard such objects as an airplane, river/sea vessels and to analyse them.

It is planned to carry out similar testing for conditions of measuring onboard the plane (or the helicopter) during aerophotogrammetry for the estimation of reliability of differential GPS-positioning while maneuvering and for the expediency of application of currently analyzed technologies of positioning.