GPS NETWORKS AND GPS MEASUREMENTS IN THE REPUBLIC OF MACEDONIA

ITRF 94 Network During the conduct of this observation, the following precise GPS receivers were used: Trimble 4000 SSE and Trimble 4000 SSI. Based on the information received from the Inter -national GPS Service, obtained through calculation, the coordinates for the surveyed points in the reference system ITRF 94, for the epoch 1996.6 were obtained. The definition of the datum on the system ITRF 94 and the epoch 1996.6 was achieved by orientation of the surveys towards the four ITRF stations (Wettzell -1202,

Matera, Graz-Lustbuehel and Zimmerwald) which also belong to the same reference system and datum (Picture 2) Picture 2 GPS points encompassed by the strategy for triple definition of coordinates on the points for international merging with ITRF 94 –network SGEM 200 6 - Section III 245 Table No.1 contains approximate coordinates of all ITRF points included in the campaign. Table No.1 Survey location EUREF Number of point (o ') (o ') Wettzell –1202(D) 0035 49 08 12 52 Graz -Lustbuehel(A) 0061 47 04 15 29 Matera (I) 0068 40 38 16 42 Zimmerwald (CH) 46 53 07 28 Ankara (TR) 39 53 32 45 Penc (H) 47 47 19 17 Dionysos (GR) 7515 38 05 23 56 Ilin Vrh (HR) 0734 42 29 18 23 Sofia (BG) 0556 42 33 23 23 Korab (MK) 0801 41 46 20 32 Ramno (MK) 0802 42 11 21 27 Borova Cuka (MK) 0803 42 00 22 52 Bogoslovec (MK) 0804 41 42 21 58 Visoka Cuka (MK) 0805 41 20 22 47 Kajmakcalan (MK) 0806 40 56 21 47 Galicica (MK) 0807 40 56 20 50 Beside the seven points for international merging of Macedonia with the International Reference ITRF 94 Network, 25 points belonging to the zero series were additionally observed using GPS, from which a certain num ber of points are used to carry out GPS control in the air traffic. ESTABLISHMENT OF PERMANENT STATIONS During the conveyance of the GPS campaign in 1996, a permanent station in Ohrid was placed, as a point being part of the European GPS Network. In the area called “Tumba”, in the flat part of Ohrid, a pillar was built and an antenna was placed for permanent reception of signals, which are registered in a PC located in a specially built facility, positioned in the vicinity of the point. (Picture 3) The registration of the signals from the geodetic satellites in the permanent station in Ohrid is carried out continuously 24 hours a day, on every 15 seconds, and every registered signal is automatically transferred in the Federate Authority for Geodesy and Cartography in Frankfurt (Germany), where the signals are being 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 246 processed, and after the processing, they are transferred to other users using the INTERNET. In future, one of the top priorities of the modern Geodetic Authority in R. Macedonia shall be the establishment of more permanent stations – (local), in order to start the operation of the so called active network . Picture 3 Permanent GPS station in Ohrid LATEST GPS SURVEY S IN MACEDONIA At the beginning of 2004, for purposes of the survey conducted in order to produce new topographic maps in scale of 1:25000, large scale GPS surveys were undertaken by which a larger number of points on the territory of R. Macedonia were encompassed. (Picture 4). Picture 4 Scheme of closed polygons for GPS surveys required for production of new maps in scale 1:25000 SGEM 200 6 - Section III 247 By using 9 trigonometric points from I line, 17 points from the city trigonometric points and 24 newly defined points, the territory of R. Mac edonia was divided in 18 closed polygons, and between two neighboring polygons there were at least 2 colliding (mutual points). One-day three hour sessions were conducted on all points, in all polygons with appropriate GPS recei vers. Using this manner, a positioning of the largest number of points on the territory of Macedonia was carried out, after the campaign EUREF 1996 GPS. Although with much lower accuracy, these surveys are very important, because they are considered to be the groundwork for new GPS campaigns in R. Macedonia. CURRENT (SEPARATE) GPS SURVEYS IN R. MAC EDONIA In conditions when in Macedonia the condensing of the GPS networks has not been performed, and when there are no permanent stations (i.e. when the so called “active network” does not exist) and when the detail geoids undulation has not been defined, the separate GPS surveys are performed by using the locally defined parameters of the Helmert transformation. This most applicable transfor mation model which establishes a direct link between the local and the global geocentric coordinate system is presented with the well known matrix equation: localxy WGS Z

    In order to determine the unknown transformational parameters for the entire territory of R. Macedonia, the data of 14 identical points with the known geocentric (WGS 84) and rectangle (Gauss -Krieger) coordinates in the global and the local coordinate system have been used. The transformational parameters, for the entir e territory of R. Macedonia, acquired by adjustment, according to the method of indirect surveys, have the following values (Table No.2): Table No.2 Parameters Values Translation round the X axis 607.148 m Translation round the Y axis 242.159 m Translation round the Z axis 491.510 m Rotation around the X axis -4.9455" Rotation round the Y axis -0.3197" Rotation round the Z axis 15.2781" Scale (ppm) -16.4374 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org Int er nat ional Confer ence SGEM 200 6 248 It should be emphasized that by using this model, a relatively high pos itional accuracy has been obtained, from 0.14 m (for the Ograzden point) up to 0.48 m (for the Ruen point). This accuracy can satisfy all mapping needs, except the accuracy required for more exact field geodetic surveys. In order to achiev e positional accuracy in more acceptable limits, a definition of se-veral regional transformational parameters has been unde rtaken, which can be used to perform more accurate geodetic surveys. For the area of the capital city Skopje - with the use of 6 identical points of the urban trigonometric network, the following 7 parameters for tran sformation of the coordinates from the local coordinate system of Bessel ellipsoid into the global (WGS 84), have been obtained (Table No.3): Table No.3 Parameters Value s Translation round the X axis 809.310 m Translation round the Y axis 102.787 m Translation round the Z axis 467.907 m Rotation around the X axis -3.5984" Rotation round the Y axis 4.0441" Rotation round the Z axis 8.9323" Scale (ppm) -23.3757 The local transformational parameters for the cities of Stip, Kocani, Struga,

Kicevo, Debar, Gostivar are obtained by defining the coord inates through positioning of points of the urban trigonometric networks, with the help of which greater positional accuracy is acquired. An adequate equalized accuracy can not be obtained for the third dimension (the height), because the local geoids undulation is not known. SUMMARY From the above -stated, it can be concluded that with the help of the methodology for deter mining the regional transformational parameters, the positional errors of the performed GPS surveys can be reduced to acceptable limits, but this does not apply to the third (the height) dimension. However, in absence of fundamental solutions for performin g highly accurate GPS surveys in Republic of Macedonia, the method for determining the regional transformational parameters is an extorted, but useful sol ution. At the same time it can be concluded that the primary condition for solving this acute geodetic issue in R. Macedonia is to undertake adequate astro-geodetic surveys for defining the local geoid, after which, unique transformational parameters for uniform transformation of the local geodetic datum into the world geodetic system WGS84 could be determ ined. SGEM 200 6 - Section III 249 REFERENCES

Pecalevska M. (2005): Defining of GPS transformation parameters for territory of city of Skopje , Diploma work, Faculty of Civil

Engineering, Skopje.

Ribarovski R. (2005): High geodesy , University "St. Cyril and Methodius", Skopje.

Ribarovski R., Markoski B., Srbinoski Z., Jovanov J. (2003): Application of UTM projection and geodetic system WGS 84, like a basic NATO standards in cartographic production in Republic of

Macedonia, Scientific project , Faculty of Civil Engineering, Skopje.

Srbinoski Z. (2001): Supplement to investigation for defining of new states cartographic projection , Doctoral dissertation, Faculty of Civil

Engineering, Skopje. 6th International Multidisciplinary Scientific GeoConference SGEM2006 www.sgem.org