TS03G – GNSS CORS Networks Case Studies (Flash), 5247 [617167]

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 1/11Positioning System GPS and RTK VRS Ty pe, Using The Internet as a Base,
A Network Of Multiple Stations

Gabriel B ĂDESCU, Ovidiu ȘTEFAN, Rodica B ĂDESCU, Mircea ORTELECAN and
Samuel Ioel VERE Ș, România

Key words : GNSS, GPS, Precision, VRS, RTK, Networks, Errors, România.

SUMMARY

Multiple reference station networks using GNSS navigation have been established for high
precision applications in many countries around the world and in Romania. Nevertheless,
real-time application is still a ta sk which is difficult to put into practice. The concept of virtual
reference station (VRS) is an efficient means of transmitting corrections to network users for
a RTK positioning. Nowadays, the challenge rega rding VRS with RTK positioning resides in
communication technologies with wireless adapta tion feeder for real-time corrections. Using
GPRS technology, a system based on VRS Internet RTK with GPRS positioning infrastructure was developed and tested. This paper talks about the VRS data transmission
mechanism, and offers an overall image over VRS with generated RTK positioning data. The results of the tests are presented in order to be able to evaluate the performance of the above
mentioned system. The results show that based on VRS Internet and RTK positioning, one
can achieve a little over 2-3 centimeters accuracy in horizontal position.

Precision when it comes to height is found in the interval 2-5 centimeters, depending on the
precision of the quasi-geoid, for transformati on in the national alt itude system (normal
altitude system Black Sea 1975).

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 2/11

Positioning System GPS and RTK VRS Ty pe, Using The Internet as a Base,
A Network Of Multiple Stations

1. INTRODUCTION

GPS Real Time Kinematics (RTK) positioning b ecomes ever more important for many GPS
precision applications – high-precision photogrammetry, topography, constructions,
agriculture, and precision, like: the Ge ographical Information System (GIS).
Basically, a mobile receiver need s a field reference station at approximately 8-12 km, in order
to insure the centimeter precision level. Recently, more networks which use the reference stations have been installed in many countries around the world and they surpass the limits of
the standard RTK systems. Over the years, different approaches have been tested in order to take advantage of the
existing multitude of reference stations, menti oning here the doctorate thesis entitled “Some
contributions regarding the use of GPS t echnology in cadastre surveys” – Gabriel B ădescu-
2005. A great part of the research involved the spatial modeling of di stance errors – base
station receiver (errors mainly regarding the io nosphere and, on the side, of the troposphere).
Nevertheless, the research was made on a distri bution of these corrections for the potential
GPS users located inside and around the GPS RTK positioning system and must be appropriately handled before the effective construction of the multiple reference station network and application (Fotopoulos et al, 2001).
Recently, using the VRS (Virtual Reference St ation) as a concept was suggested by many
research groups as a more reliable approach for transmitting and correcting inside the
information network for the RTK network user s (see Wanninger, 1997; Vollath et al,. 2000;).
This approach does not require a reference station from a physic al point of view.
On the other hand, it allows the user to ha ve access to data coming from a non-existing
reference station, but virtual in any location in the permanent station network’s cover area.
Among other facilities, the VRS approach is mo re flexible in what concerns allowing the
users to use their current receivers and softwa re without involving any special software in
order to simultaneously administra te the corrections in a series of reference stations(G.R. Hu
et al, 2002). With regards to the Virtual Referen ce Stations (VRS), the users in the reference
station network can operate constantly at gr eat distances, while precision only slightly
changes (a couple of centimeters). However, there must be a communication connection for
transmitting reliable VRS data from a control centre to a receiver which is being used as a
mobile receiver (rover) by the user.

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 3/11There are more ways to transfer GPS data for RTK positioning.
For certain wireless transmission services ther e are frequency and power restrictions, which
regulate the use of such data transmission devices. GSM is a widely available public service
and can be used as a distributi on channel for VRS data (Vollath et al, 2000.). Using GSM as a
communication link is, unfortunately, relatively expensive, because GSM data transmission
services are very expensive and the cover areas differ from one GSM carrier to another (G.R.
Hu et al, 2002).
From an operational point of view, cost is a very importa nt aspect especially in the context we
are in, meaning a crisis, especially in Romania. This cost can be reduced by using the GPRS
technique (General Pack et Radio Service).
Each wireless communication module has pro and against arguments related to it, but must,
generally, support the VRS and RTK data transm ission connection with small data latency,
good performance in moving the m obile receivers, cheap user equipment and national service
cover. The main objective of this paper is to demonstrate once more that the new method mentioned below based on Internet and GPRS positioning using RTK and VRS. The transmission of VRS data based on the Intern et is a communication method which is being
tested and discussed, regardi ng the results of the field te sts made using the Romanian
Positioning System, GNSS system named ROMPOS, in order to evaluate the performance of the suggested system.

2. GENERAL PRESENTATION OF THE VIRTUAL REFERENCE STATIONS
(VRS) USED IN ROMÂNIA
This paper will present the VRS used in Romani a and of the NTRIP utilitarian together with
the Internet, when transmitting data. In order to create data at a virtual referenc e station from the observations in the Real
Reference Stations National Network, there are a number of processing steps which must be
taken in order to reach the data. The first step is to solve the double-difference phase ambiguities between the network’s stations. One can observe that the double-difference phase ambiguities between the network’s stations
must be known, together with the precise coordinates for the reference stations.
The reference stations’ coordi nates can be provided by the Geodesy Department, through the
National Geodesy Fund service, in the case of a permanent national and regional reference
network for the National Network of Permanent Stations. Alternatively, these coordinates can
be obtained through a static measurement on ev ery station over long pe riods of time, using
also the traditional long-area effect procedure for static positioning. However, even with a
precision of the known coordinates, it is not eas y to establish ambiguities between reference
stations for the real-time network, because time is short and the stations are at approximately
60-70 km away from each other. In order to support the RTK positioning method, the whole ambiguities of the double-differences between the reference stations of the network must be solved in real-time, because
these ambiguities should be instantly recalculat ed in case the satellite constellation changes
and new satellites appear, or the connection with the ones located in the receiving area is lost

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 4/11or the delay is longer for the received data. At this point, an adjusted residual Kalman filter is
suggested, to solve the double-difference phase ambiguities between the stations of the observed network, filter which has the ability to be used in real-time. This method, using the
Kalman filter, is based on data which was recei ved at previous dates and not only in current
ones. So as to help in solving the ambiguities in th e network process, the er ror caused by orbits can
be reduced or eliminated using type IGS orbits , ultra-fast predictable Orbit (IGU), instead of
emissive orbits. Exact ephemeredes can be obt ained from GPS International Service (IGS),
ephemeredes centers, which include a day of predicted orbits.
After the double-difference ambiguities associ ated with reference stations have been
established at their correct va lues, the terms for the so-called correction for atmospheric
deviations regarding the troposph ere and ionosphere and other errors can be generated as
residual in the L1 and L2 phase measurements from satellite to satellite and from one date to
another(G.R. Hu et al, 2002). The purpose of these corre ctions is to reduce the influence of
spatially correlated errors. This means that, when the user applies corrections to the code and
the phase observations, the influence in the a tmospheric errors and other errors shall be
reduced or eliminated. This leads to improving the positioning performance in the network in which it is calculated and the measurements are made. There are numerous methods to set
corrections for the user paper mentioned above showed that performan ce, regardless of the
method used, is the same. In the following step, the VRS data for user rece ivers are generated because it is necessary. In
order to generate VRS data if there were no reference stati on at the user’s location, the
approximate position of the user an d the position of the user related to this VRS, in relation to
the transport carrier and the pse udo-range observations at the mast er reference station must be
geometrically moved and improved, by applying corrections to the network according to the approximate position of the user, namely the VRS position. The approximate position of the
user can be obtained through absolute GPS positioning or positioning code.
The approximate position of the user can be obtained through absolute GPS positioning or by using the codes. After this, the VRS data are generated as a RTCM or CMR format and are then transmitted to the users. In order to generate VRS data we need to fulfill three steps. The first step is to solve
the double-difference ambiguities for phase measur ements in real-time, between the stations
in the network inside of which the work occurs. The second step is to generate correlations for
a satellite used as a base satellite, date by date for the users of the network in which the
measurements are made, according to the user’s approximate position. The third step is to
transform the VRS data into RTCM format or CMR messages, by applying correlations to the
master reference station data and by then sendin g them to the location requested by the users
as VRS data. VRS data are then transmitted to the user as unique RTK correlations of the reference station for the receiver. The receiver ca n then use these correlations as if there were
a unique approach of the reference station for RTK.

3. THE VIRTUAL REFERENCE STATIONS (VRS) HAVE MORE WAYS OF
TRANSMITTING THE DATA FOR A VERY ACCURATE POSITIONING.

An efficient communication conne ction is essential for Virtual Reference Station (VRS) and

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 5/11for RTK positioning, because the transfer in due ti me (real time) of the VRS data is necessary
for such a system. The communication connection must insure reliability in transferring the
data and should not cause any significant delay in the transmission time. It is expected that,
also, the links are to be without restrictions, so as to cover a wide range of users. Up to now,
there are a number of practical manners of distri buting the VRS data to users in real time, like
GSM and the Internet (Hada et al , 1999;. Vollath et al, 2000;. Liu și Gao, 2001; Ko et al ,
2001). In the case of a developed mobile telephone network, the easiest transmission mechanism is
GPS technology, because it holds the lowers risk of data loss. A mobile phone allows the bi-
directional communication between a user and the data control center of the VRS, so, the user
can transmit his approximate position to the control center. Other advantages include the fact that there is no need to apply radio frequencies which are limited to the maximum power of 1 wat, and the lo w cost of installing this system. One of the
disadvantages of GSM is the limited number of us ers at the same time dictated by the control
center, because each GSM line can only support a single user, but there is some software which simulates more users (the Trimble Comp any). Another important disadvantage of GSM
is its high price, because the user must be c onstantly logged while the RTK system with VRS
is being used. There is, also, the possibility to use the Inte rnet as a data connection between the control
center and the user. The Internet is the worldw ide network system which is, and will become,
the most important means of common communicati on, mostly viewed from the point of view
of its fast data transmission rhythm, and the opening to an unlimited number of users. The
Internet uses bi-directional communication and, because of this, the user can also send his
approximate position and his requests to the cont rol center, and then the control center can
provide data to the Virtual Refe rence Station (VRS) for the request of each user according to
his approximate position. With the Internet’s increased capacity and recent developments in communications
technology, especially in what concerns GPRS technology, th e Internet is a trustworthy
choice for transmitting GPS data of the VR S type for RTK positioning, through a GPRS.
Using the GPRS technology we can send and receive information directly from the Internet,
the media for transferring the VRS data thro ugh the Internet being favorable, and much
cheaper than the GSM telephone media. As a re sult, a GNSS system with Virtual Reference
Stations (VRS) and Real Time Kinematic (RTK ) through the Internet is being used in
Romania and it is a NTRIP type (the system was developed by a specialized university in
Germany). This system uses GPRS technol ogy as a communication connection between the
control center which is coordi nated by the ANCPI and administ rated by ROMPOS and the
stations which are made use of by the users.

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 6/11

Fig.1. Setup of Internet-based VRS RTK positioning via GPRS (G.R. Hu et al, 2002).
Consequently, a GNSS system with Virtual Reference Stations (VRS) and Real Time
Kinematic (RTK) through the Internet is being us ed in Romania and it is a NTRIP type (the
system was developed by a specialized univers ity in Germany). This system uses GPRS
technology as a communication co nnection between the control center which is coordinated
by the ANCPI and administrated by ROMPOS and the stations which are made use of by the
users. The observation files for each reference station are transmitted to a control center (ANCPI-
ROMPOS), using the Internet. The user is e quipped with a RTK receiver and a pocket PC
with GPRS or a mobile phone, as shown in I llustration no. 1. This user uses the client
software to connect to the control center server (ANCPI-ROMPOS) through GPRS Internet,
and his approximate position is transmitted to th e control center. The control center software
(ANCPI-ROMPOS) automatically receives the user’s approxim ate position and selects the
closest reference station for the user as a master reference station (the permanent stations in
the A class GNSS Network or the A class EUREF stations). The raw data from the reference
station are then corrected as a geometri cal position and improved by applying network
corrections according to the user’s approximate position. This is in a VRS data format, which
is then transmitted as RTCM or CMR message s to the user’s receiver through the GPRS
Pocket PC serial port, at a rate of 9,600 bps or greater.
The receiver can then use these messages as is the case with the unique reference RTK
stations. Six testing points in the North and North-West part of Romania (Class A stations), with
different distances from the master reference stat ion have been used in order to test the new
communication method, as shown in fig.2. Using the Internet and GPRS are of good omen
and they bring a level of novelty and at the same time a saving in what concerns the price of
data transmissions.

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 7/11

Fig. 2. România Integrated Multiple Reference Station Netw ork (ROMPOS) and Internet-based VRS RTK test stations

The test site of the testing center identified as ȚAPU is considered to be the first example,
17,3 km away from the BAIA master referen ce station. A Leica 1200 with a dual receiver
frequency was used together with a GX1230 ante nna. This test was ca rried out in the time
interval 10:23-15:45 UTC (12:23- 17:45 local time), on July 25st 2010.
The real-time positions during the test have been continuously recorded in the receiver’s memory. As a result, the real base position could be calculated before, if the connection to raw data is made. The standard deviations (interio r precision) of East path and North, and the height elements
are 0.015m, 0.012m and 0.024m. As it was expected, the standard deviation in the horizontal
position is a factor with 1,5-2 better than in height. The reason for the significant
compensation in the height elem ent is caused by the tropospher e residual delay, which has a
much greater effect than th e horizontal coordinates.
One can observe that 99% horizontal (2D) posi tion precision is smaller than 2 cm and 99%
vertical position precision is smaller than 4 cm.
Besides precision, a crucial factor in using th e operational usage of the RTK GPS is the speed
with which it can initiate (e.g. to solve complete ambiguities). Th is is expressed as TTF (Time
To Fix) or TTFA (Time To Fix Ambiguities) va lue (Edwards et al, 1999; Wübbena et al
2001). TTF of RTK refers to the observation mome nt which is required in order to solve
complete ambiguities in real-t ime, after re-initiation.
Six seconds after each successful fix – or 2 minutes at the most, if the fix did not take place –
the RTK receiver engine is totally reset. In c onsequence, a TTF analysis was possible. For the
ȚAPU radio station, the time of th e test series TTF for RTK vs. the number of satellites and a
HDOP value. The initiation time and the precision were analyzed on all testing stations which were used. In
this section, the six trial stations were comp ared in order to evalua te performance based on

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 8/11Internet VRS with RTK positioning in different locations in Romania, and the results are
presented in Table no.1.

Test Station
Distance from Master
Reference Station (km)
Standard Deviation (m)

Northing Easting Height
ȚAPU 17.3 0.015 0.012 0.024
SEINI 20.3 0.015 0.024 0.040
TURȚ 20.7 0.016 0.017 0.038
FELDRU 12.3 0.013 0.015 0.039
ODOREU 4.2 0.012 0.005 0.021
JIBOU 25.3 0.011 0.016 0.046

Initiation is much more difficult when there is a greater PDOP value and fewer satellites. The
reason for greater dispersion at certain times is the weak satellite geometry, which leads to a
higher PDOP value. It is responsible on many o ccasions, because ambiguities have to be set
each time.

4. CONCLUSIONS AND SUGGESTIONS

The precise RTK positioning on longer distances requires a GNSS reference stations network,
which presently has an average density of 60-70 km between them. In Romania, the
Romanian Positioning System named ROMPOS has b een used for almost 2 years. It is based
on Internet with the use of VRS and RTK technology, GPRS positioning infrastructure and
NTRIP which was developed and is used in Romania. The active operation of the multiple reference stations network in Romania and the various field tests in different locations in
Romania confirmed the fact that horizontal prec ision is much better, roughly 2-3 cm, and the
vertical one still depends on an exact determination of the quas i-geoid with 2-5 cm precision,
which can occur with an initiati on time of less than 1-2 minutes.
Based on the Internet, the system which us es VRS and RTK real-time positioning technology
has a precision of centimeters and is used at th e level of services in constructions, fast
topography and GIS. With a better communica tion through the wireless technologies and
RTK positioning using multiple VRS reference stations if used, we will be able to see it being
used, very soon, in different domains across the world and especially in Romania.
References [1] Chen X.M., Han S.W., Rizos C., Goh P.C. (2000) Improving real-time positioning
efficiency using the Singapore Integrated Multiple Refere nce Station Network (SIMRSN) , Proc
13th Int. Tech. Meeting of the Satellite Divisi on of the U.S. Inst. of Navigation, ION GPS-
2000, Salt Lake City, September 19-22, 9-16. [2] Fotopoulos G., Cannon M.E. (2001) An overview of multi-reference station methods for
cm-level positioning , GPS Solutions 4(3): 1-10.
[3] Han S.W. (1997) Carrier phase-based long-range GPS kinematic positioning , Ph.D.

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 9/11dissertation, rep. UNISURV S-49, School of Geomatic Engineer ing, The University of New
South Wales, Sydney, Australia. [4] Hu G.R., Khoo H.S., G oh P.C., Law C.L. (2002) Testing of Singapore In tegrated Multiple
Reference Station Network (SIMRSN) fo r precise fast static positioning , Proceedings of the
European Navigation Conference-GNSS2002, 27-30 May, Copenhagen, Denmark, CD-ROM.
[5] Muellerschoen, R., W. Bertiger, M. Lough (2000) Results of an Internet-Based dual-
frequency Global Differential GPS System , Proceedings of IAIN World Congress in
Association with the U.S. ION 56th Annual Meeting, San Diego, California, June 26-28,
2000.
[6] Teunissen P.J.G., Kleusberg A. (eds) (1998) GPS for Geodesy . 2nd enlarged edn.
Springer, Berlin Heidelberg New York. [7] Vollath U., Buecherl A., Landau H., Pagels C., Wager B. (2000) Multi-base RTK
positioning using virtual reference stations , Proc 13th Int. Tech. Me eting of the Satellite
Division of the U.S. Inst. of Navigation, ION GPS-2000, Salt Lake City, September 19-22,
123-131. [8] Wanninger L. (1997) Real-Time differential GPS-error modeling in regional reference
station networks , Proc. of the IAG Scientific Asse mbly, Rio de Janeiro, Sep. 1997, IAG-
Symposia 118, Springer Verlag, 86-92. [9] Wübbena G., Bagge A., Schmitz M. (2001) RTK network based on Geo++@ GNSMART-
concepts, implementation, results , Proc 14th International Techni cal Meeting of the Satellite
Division of the Institute of Navigation, Salt Lake City, USA, ION GPS-2001, September,
368-378.
BIOGRAPHICAL NOTES

Lecturer.univ.dr.ing. Geodesy Gabriel B ĂDESCU,
Birth date: March 27, 1973, Employment: The Northern University, Baia Mare, Teaching position: Lecturer, Undergradua te education: The Faculty of Geodesy, Bucharest, 1997,
Scientific titles and activity: PHD Doctor of Engineering Sciences, with the major of Civil Engineering, in the area of expertise of Ge odesy, Cartography, Fotogrammetry and Remote
Sensing, Astronomy, GPS, GIS. Professional activity: Geodesy engineer, 1997-1999, ISPE(RESEARCH AND DESIGN INSTITUTE OF ENERGY), Bucharest,

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 10/11Assistant, 1999-2005 TECHNICAL UN IVERSITY OF CIVIL ENGINEERING
BUCHAREST, Senior lecturer, 2006-pr ezent, the teaching lines of Geodesy, Cartography,
Fotogrammetry and Remote Sensing, Astr onomy, GPS, geodetic network design and
optimization , The Northern University, Baia Mare. Articles published abroad, in international field journals, in the books of some international scientific meetings;
170(60 ISI), Published Books, Manuals, Workbooks of problems and Tutorials: 10.

CONTACTS
PhD Lecturer .Gabriel N. B ĂDESCU,
North University Baia Mare,
Department Geodesy of Mines
str.Victor Babes nr.62 A
430083 BAIA MARE, Maramures, ROMANIA Phone 0040262289226, Mobile 0040723899714 ; 0040749387147 Fax 0040262276153 Email gabrielbadescu@yahoo.com , gabrielbadescu3000@gmail.com
Web site: www.ubm.ro

CONTACTS
PhD. Associate Prof. Eng. Ovidiu Ștefan,
North University Baia Mare,
Department Geodesy of Mines
str.Victor Babes nr.62 A
430083 BAIA MARE, Maramures, ROMANIA Phone 0040262289226, Mobile 0040744630254 Fax 0040262276153 Email o.stefan@ymail.com, Web site: www.ubm.ro
CONTACTS
Master.ing.Rodica B ĂDESCU,
North University Baia Mare,
Department Geodesy of Mines
str.Victor Babes nr.62 A
430083 BAIA MARE, Maramures, ROMANIA Phone 0040262289226, Mobile : 0040741395916 Fax 0040262276153 Email badescu_rodica@yahoo.com Web site: www.ubm.ro

TS03G – GNSS CORS Networks Case Studies (Flash), 5247
Gabriel B ădescu, Ovidiu Ștefan, Rodica B ădescu, ,Mircea Ortelecan and Samuel Ioel Veres
Positioning System GPS and RTK VRS Type, Using the Internet as a Base, a Network of Multiple Stations
FIG Working Week 2011
Bridging the Gap between Cultures Marrakech, Morocco, 18-22 May 2011 11/11CONTACTS

PhD University Professor Eng. ORTELECAN MIRCEA
ortelecanm@yahoo.fr
CONTACTS

PhD. Associate Prof. Eng. VERES IOEL SAMUEL
veresioel@yahoo.com