Survey Review ISSN: 0039-6265 (Print) 1752-2706 (Online) Journal homepage: http://www.tandfonline.com/loi/ysre20 Chronology of the development of geodetic reference networks in Serbia Oleg Odalović, Miljana Todorović Drakul, Sanja Grekulović, Jovan Popović & Danilo Joksimović To cite this article: Oleg Odalović, Miljana Todorović Drakul, Sanja Grekulović, Jovan Popović & Danilo Joksimović (2016): Chronology of the development of geodetic reference networks in Serbia, Survey Review, DOI: 10.1080/00396265.2016.1249998 To link to this article: http://dx.doi.org/10.1080/00396265.2016.1249998 Published online: 15 Nov 2016. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ysre20 Download by: [University of Otago] Date: 15 November 2016, At: 11:09 Chronology of the development of geodetic reference networks in Serbia Oleg Odalović Jovan Popović ∗ , Miljana Todorović Drakul and Danilo Joksimović , Sanja Grekulović , In this paper, the development of geodetic reference networks in Serbia is shown. This historical summary covers the time from the first organised work in 1855 until today. Special attention has been paid to the establishment of the modern network using Global Navigation Satellite Systems (GNSS). Within the networks established by GNSS, two last realised networks are especially distinguished. The first one is a classic spatial reference network SREF (Serbian Reference Frame) established in 2003, and the second one is a permanent stations network – AGROS (Active Geodetic Reference Network of Serbia) realised in 2006. Keywords: GNSS, Coordinate Reference Systems (CRS), Reference frame, Permanent stations, Coordinate transformation Introduction Works on the compilation of geodetic networks in Serbia have been continually performed in the last 150 years. Many institutions contributed to their creation in that period: . Military Geodetic Institute from Vienna (MGI), . Main Military Headquarters Geography Department of the Kingdom of Serbia (MMHGD), . Military Geographic Institute of the Kingdom of Serbia (MGIS), . Military Geographic Institute of the Kingdom of Serbs, Croats and Slovenians (MGISCS), . Military Geographic Institute of the Kingdom of Yugoslavia (MGIY), . Federal Geodesy Administration of the former Socialistic Federative Republic of Yugoslavia (FGAY), and . The Republic Geodetic Authority of Serbia (RGA). Work on the development of the first-order trigonometric network in the former Austro-Hungarian monarchy was commenced in 1855 by MGI. MMHGD continued with its work in 1899 for the development of trigonometric networks in the former Serbia, Macedonia and Montenegro. After the First World War, further work on finishing the first-order trigonometric network was done by MGIS, and after the Second World War, work on the network densification was continued by FGAY. In 1974, FGAY was transformed, and the maintenance and development of reference positioning networks passed into the jurisdiction of each republic of the former Socialistic Federative Republic of Yugoslavia. The same institutions established a levelling network across the Western Balkan countries. There was no organised maintenance or establishment of geodetic networks in Serbia between 1974 and 1996. Faculty of Civil Engineering – Department of Geodesy and Geoinformatics, University of Belgrade, Belgrade, Serbia ∗ Corresponding author, email: odalovic@grf.bg.ac.rs © 2016 Survey Review Ltd Received 7 June 2016; accepted 12 October 2016 DOI 10.1080/00396265.2016.1249998 Formal and legal conditions for the maintenance and future network development were secured through the establishment of RGA in 1992. A special department within RGA was formed in 1996 to be responsible for the establishment of geodetic reference networks. In the same year, work on creating the passive geodetic network using GNSS started, and the network was formally finished in 2003. At the same time, the network of permanent stations in Serbia was planned and realised (Active Geodetic Reference Network of Serbia – AGROS) which represents the latest network in Serbia. Trigonometric networks MGI started organised work on establishing geodetic networks in contemporary Serbia way back in 1855. MGI established the first-order trigonometric network of the former Austro-Hungarian monarchy, as well as a part of a trigonometric network in the states of the contemporary West Balkans, which at that time were an integral part of the Ottoman Empire (Kovács and Timár, 2009). MGI applied the concept of triangulation chains throughout the work, where the following chains were developed (Fig. 1): . In the region of northern Serbia (eastern part of contemporary Vojvodina) and the chain from Slovenia to Montenegro over Bosnia and Herzegovina from 1855 to 1857, . The chain covering a part of Slovenia, a part of Croatia and the northern part of contemporary Serbia was established in 1872, and . The chain over Bosnia and Herzegovina which was established later by connecting the above two chains. At the same time, MGI developed a triangulation chain throughout the central part of today’s Serbia, which was later used for the establishment of the first official trigonometric network in Serbia (Fig. 2). Survey Review 2016 1 Odalović et al. Chronology of the development of geodetic reference networks in Serbia 1 Triangulation chains in the west Balkans established by MGI 1855–1875 2 Trigonometric networks in Serbia, Macedonia and Montenegro dating from 1899 to 1923 2 Survey Review 2016 Odalović et al. Chronology of the development of geodetic reference networks in Serbia These chains were based on Bessel’s ellipsoid and classical geodetic datum: . The astronomical coordinates of the point Hermannskogel situated in the vicinity of Vienna were fixed, . The network itself was oriented by azimuth of the Hermannskogel–Hundsheim Berg trigonometric side. Astronomical coordinates of the points were determined mainly in cities (Kovács and Timár, 2009), and the figure of the chains was established by measuring angles and by base extension networks (Bratuljević et al., 1995). In the nineteenth-century triangulation, which was established by MGI Vienna, the longitudes of the points were originally referenced to the prime meridian of Ferro (Timar, 2007). In the twentieth century, Ferro was abandoned as the prime meridian, and Greenwich was adopted. Slightly different values for the Ferro–Greenwich longitude difference were adopted in the Balkans compared to Austria. In Greenwich terms, there is a discontinuity in the longitudes of the MGI Vienna network between Austria and Yugoslavia. The Greenwich longitude of the Hermannskogel origin adopted in Austria is 16°17′ 41.06′′ E and in Yugoslavia 16°17′ 55.04′′ E (Mugnier, 1997). The difference is equivalent to approximately 350 metres. This manifests itself in coordinate transformations between the MGI triangulation and the European Terrestrial System 89 (ETRS89) having significantly different parameter values in Austria and the former Yugoslavia. MMHGD relied on the works performed by MGI and the development of trigonometric networks in the former Serbia, Macedonia and Montenegro started in 1899 (Fig. 2). Work stopped during the First World War with the networks being formally finished in 1923 by the Military Geographic Institute of the Kingdom of Serbs, Croats and Slovenes (MGISCS). To resolve the problem of coordinate system origin and rotation of the network, 7 points on the shores of the river Drina determined by MGI were adopted (points marked by black dots in Fig. 2). To resolve the problem of network scale, several base extension networks were used (extension base lines are shown in Fig. 2 with thickened lines). By combining all the chains and networks over a few decades, the first trigonometric network in the present Serbia was formally established (Fig. 3). According to the first Law of Real Estate Cadastre and Surveying that took effect in 1932, trigonometric network was officially adopted as a base network for horizontal positioning in Serbia. This trigonometric network has never been adjusted as a whole, i.e. it consists of several sub-networks. From Fig. 3, it can be seen that the network consists of three parts. The largest part covers the central part of Serbia (the part is shown in Fig. 3 by full lines), then the part covering the northern part of Serbia (the part is shown in Fig. 3 by dotted lines) and the northwest part of Serbia (the part is shown in Fig. 3 by thickened lines). Densification of the network continued, so that by the end of the twentieth century there were over 57,000 trigonometric points in Serbia (Fig. 4). Nominal coordinates’ accuracy of trigonometric points was not greater than 10 centimetres. 3 First-order trigonometric network from 1932 4 Trigonometric network points after densification Survey Review 2016 3 Odalović et al. Chronology of the development of geodetic reference networks in Serbia It should be noted that all points have never been maintained in an organised manner, but only when needed, and in accordance with the Cadastre and Survey Law. Astrogeodetic network Along with establishing these points, especially after the Second World War, astro-geodetic determinations were established for the creation of an astro-geodetic network. However, plans for forming astro-geodetic networks have never been realised. The results of this survey can be found for only 25 points in archives in Serbia (Fig. 5). Levelling networks All of the above-mentioned institutions took part in the development of the levelling networks in the West Balkan countries. The levelling network in Slovenia, Croatia, and northern part of Serbia, western Bosnia and Dalmatia were developed by MGI from 1873 to 1909. This network consisted of 19 loops and is shown in Fig. 6. Measurements were done by applying geometric levelling, and all heights were connected to the tide gauge in Trieste (Bratuljević et al., 1995). MMHGD used the levelling network, developed by MGI, to extend the network into today’s central Serbia, Montenegro and Macedonia from 1909 to 1931. This network consisted of several parts and 15 loops (Fig. 7). The northern parts of this network were created in order to connect to the levelling network developed by MGI. On the basis of these two mentioned networks MGIS, with some additional measurements carried out between 1931 and 1941, established a network entitled as the First High Precision Levelling Network in the Kingdom of Yugoslavia (Fig. 8). The heights of benchmarks were treated as normal-orthometric heights (H ), but the network itself was never adjusted as a whole (Bratuljević et al., 1995). It is important to mention that this network was used as the base for the determination of heights for trigonometric points, mostly by applying the trigonometric levelling method. Besides this, heights of the benchmarks in the network were determined without any information about the gravity field. This network was also the base for all vertical positioning for the Socialistic Federative Republic of Yugoslavia till 1963. From 1963 to 1967, FGAY created plans for a completely new levelling network, which was established from 1970 to 1973, according to the suggestions of the International Association of Geodesy and was called the Second Levelling Network of Yugoslavia. All the necessary calculations for this network were done by the end of the 1990s, and the heights were calculated in all most used physical height systems. Accuracies of up to 2 centimetres were achieved on benchmark heights. Unfortunately, because of the situations in the former Yugoslavia and its disintegration, this network was never officially used in Serbia, but data from the network are still publicly available for scientific research. Modern reference frames The Department of Geodesy, Faculty of Civil Engineering, Belgrade University, conducted a study under the title Geodetic Reference Networks towards the end of 1995, where the creation of new geodetic networks in Serbia was suggested (Bratuljević et al., 1995) which . Included points from Serbia within the European Reference Frame (EUREF) network and . Created a totally new network using satellite technology. The first EUREF campaign 5 The spatial distribution of the points where geographic coordinates were determined by the astrogeodetic method 4 Survey Review 2016 The survey campaign, Balkan 98, was realised in 1998 with the aim of including the Republic of Serbia into EUREF (Altiner et al., 1999). It also included Bosnia and Herzegovina, Montenegro and Albania. There were 7 points of the first-order trigonometric network in Serbia (one of which is positioned on the border between Serbia and Montenegro). These points were established and named in administrative sense YUREF (Yugoslav Reference Frame) (Fig. 9). Between the 4 September 2008 and 9 September 1998, a GNSS survey was done at these stations by applying the static method using dual frequency receivers. Five 24-hour survey sessions were started with 15-second data registration interval for each point. The data were processed by State Cartography and Geodesy Institute of Federal Republic of Germany in Frankfurt/Main using the Bernese GPS Software version 4.0. The network was defined with the European Permanent Network (EPN) stations: Wettzell-1202 (Germany), Matera (Italia), Graz–Lustbuehel (Austria) and Zimmerwald (Switzerland) in International Reference Frame 1996 (ITRF96), epoch 1998.7. The average accuracy of the newly determined points was 2 millimetres for horizontal position and 6.5 millimetres for ellipsoid heights. Odalović et al. Chronology of the development of geodetic reference networks in Serbia 6 The Precise Levelling Network created by MGI 1873–1909 The final coordinates were obtained by transforming them into ETRS89. Serbian reference network (SREF) The Republic Geodesy Authority planned and realised the spatial reference network of the Republic of Serbia called SREF from 1998 to 2003. The network consists of a total of 838 permanently stabilised points regularly distributed over the area of the Republic of Serbia (Kosovo and Metohija province excluded) with an average spatial resolution of 10 kilometres (Fig. 9). In addition to the new planned points, points of the existing trigonometric network were included which complied with criteria primarily in the sense of spatial distribution (Blagojević , 2003). The SREF network was established to define a spatial reference system for the Republic of Serbia. Professionals of RGA accomplished all the necessary measurements for the realisation of SREF which they performed with 14 dual frequency GNSS receivers. The network was determined on the basis of the static GNSS method with sessions that lasted from 60 to 120 minutes, while the average duration of the GNSS survey was 90 minutes. A least squares adjustment of the SREF coordinates was computed using the coordinates of 7 YUREF points in ITRF96, epoch 1998.7 as fixed points. The average estimated accuracy of the newly determined coordinates was 6 millimetres horizontally and 10 millimetres for ellipsoid heights. This network has been in official use since 2003. The second EUREF campaign RGA participated in a new survey campaign EUREF 2010 in August 2010. The campaign goals were: . To densify the European Terrestrial Reference Frame in the Republic of Serbia and at the same time, densification was done for the FYR of Macedonia, during the campaign entitled MAKPOS2010, . To provide control for the State Reference System realised in previous campaigns, . To realise of a high precision reference base that will be used for scientific purposes, . Further integration of the Republic of Serbia into European geodetic activities. Twenty EPN stations, 48 stations of national permanent networks (Serbia, Macedonia, Bulgaria and Hungary) and 19 points of classic geodetic networks were included in the survey (Fig. 10). The latter 19 points included 6 points of the 1998 YUREF network, 6 points of the SREF network and 7 points in Macedonia determined within the EUREF 1996 campaign (Veljković and Lazić , 2011). The GNSS survey, which included all stations, was carried out between 1 August and 4 September 2010 using dual frequency geodetic grade receivers. The campaign consisted of five survey sessions that lasted 24 hours. The time interval between the end of one session and the start of another one was not longer than 15 minutes. A complete processing of the survey was done using the Bernese GNSS software 5.0 (Veljković and Lazić , 2011). Finally, ETRF2000 coordinates were compared to EUREF Balkan ‘98 campaign coordinates that were transformed from ITRF96 epoch 1998.7 into ETRF2000 of the same epoch. The campaign was in agreement with the previous one in the range of 20 millimetres horizontally, but there was change in height from 40 to 50 millimetres. A similar comparison was performed for SREF points which showed changes between 20 and 30 millimetres. All the coordinates in the network refer to European Terrestrial Reference System 1989 (ETRS89), i.e. to its realisation ETRF2000 for the epoch 2010.63 (SRB_ETRS89). Survey Review 2016 5 Odalović et al. Chronology of the development of geodetic reference networks in Serbia 7 The Precise Levelling Network created by MMHGD 1909–1931 Active geodetic reference network The RGA proposed the establishment of a network of permanent stations in 2001. The SAPOS network in Germany was used as a model. Using the SAPOS 8 The First High Precision Levelling Network 1 6 Survey Review 2016 model with an interstation spacing of approximately 30 kilometres, it was estimated that over 60 permanent stations would be required for this project. The EUPOS programme (European Position Determination System) Odalović et al. Chronology of the development of geodetic reference networks in Serbia Table 2 Transformation parameter values from Bessel to SRBETRS89 Transformation parameter tx ty tz ωx ωy ωz s 9 State reference network of the Republic of Serbia organised by the Berlin Senate Department for Urban Development, supported by the European Academy of the Urban Environment, was established in 2002. The members of the programme agreed to create a multifunctional Differential Global Navigation Satellite System (DGNSS) reference station system in the countries of Central and Eastern Europe using unique standards. One year later in Serbia and in concordance with EUPOS standards, the original project was changed whereby the maximum 70 kilometres distance between permanent stations was adopted. According to this, it was decided that only 34 permanent stations would be required. Two control centres and three customer services based on the concept of Virtual Reference Station (VRS) and Area Correction Parameters (ACP) were also planned. The network was finally realised in December 2005 with a configuration that partly differed from the planned one and included a total of 30 stations, one control centre in Novi Sad and fully established Real Time Kinematic (RTK) and DGNSS services both based on the VRS concept. Permanent stations were mainly installed at the buildings of the local Real Estate Cadastre offices. AGROS station coordinate values were determined by Table 1 Available AGROS services: 2016 status Current services RTK DGNSS PP Accuracy [m] 0.02–0.03 0.5–3.0 0.01 Value Standard deviation 574.02732 m 170.17492 m 401.54530 m −4.88786′′ 0.66524′′ 13.24673′′ 6.88933 ppm 0.015 m 0.015 m 0.015 m 0.032′′ 0.049′′ 0.044′′ 0.106 ppm using 6 EUREF points with coordinates referred to ITRF96 at epoch 1998.7 as well as to a series of network points: Bucharest, Graz, Istanbul, Matea, Padua, Penc and Sofia. The system was reorganised after activation, including a change of location of some AGROS network stations. Together with these changes, significant progress was made in customer services for providing VRS, RTK and Post Processing (PP) services (Table 1, Odalović et al., 2010). Presently ARGOS consists of 29 permanent GNSS stations, all equipped with Trimble receivers. Three AGROS stations (Šabac, Novi Pazar and Knjaževac) have been included in the EUREF permanent network (EPN) since September 2011. It is planned to connect AGROS with corresponding networks in neighbouring countries and with this in mind, some activities have already started (Fig. 11), namely the informal exchange of data with almost all neighbouring countries, while the contract with Hungary has already been signed. Horizontal coordinates transformation The Gauss–Krüger projection based on the Bessel ellipsoid was used in Serbia up until 1 January 2011 regardless of the realisation of EUREF and the establishment of SREF and AGROS in Serbia. As a consequence of adopting the new system, it became necessary to start the transformation of coordinates of all geodetic points in SRB_ETRS89 system as well as the transformation of all existing Cadastre and cartographic material. The first activity was to gather the coordinates of the trigonometric points in the SRB_ETRS89 system in an organised manner. Over 4000 points were gathered at an average of one point per 5 kilometres between 2001 and 2004 (Fig. 12). Using the newly determined points and the points taken over from RGA archives, seven parameters of Helmert transformation were estimated using the following equation:       X tx X Y  = (1 + s)R Y  + ty  (1) Z BESSEL tz Z SRB ETRS89 where the left side of the equation represents the geocentric coordinates X, Y, Z in SRB_ETRS89 system. The right side of the equation represents the X, Y, Z geocentric coordinates associated with the Bessel ellipsoid, tx, ty, tz are estimated translation parameters, s is the evaluated scale parameter. The rotation parameters ωx, ωy, Survey Review 2016 7 Odalović et al. Chronology of the development of geodetic reference networks in Serbia 10 Stations distribution of the second EUREF campaign in the territory of Serbia (Veljković and Lazić, 2011) 11 AGROS and neighbouring counties’ permanent stations locations 8 Survey Review 2016 Odalović et al. Chronology of the development of geodetic reference networks in Serbia 12 Spatial distribution of trigonometric points with coordinates determined in the SRB_ETRS89 from 2001 to 2004 13 Graphical representation (Popović, 2010) ωz are the elements of rotation matrix R:   v z −v y 1 1 vx  R =  −vz v y −v x 1 values themselves in grid points were determined using collocation (Moritz, 1980). The algorithm for coordinate transformations, using AGROS and transformation grids, is shown in Fig. 14b. The usage of AGROS for the determination of coordinates of new points is not burdened by any additional transformations (Fig. 14a). The above transformations refer only to horizontal position, while the problem of heights was solved by determining geoid model, i.e. a quasigeoid model for Serbia. (2) Normal-orthometric heights were used instead of the unknown ellipsoidal heights related to the Bessel ellipsoid in all transformations. Transformation parameters are publicly available, but the RGA has published parameters for only 1217 common points, which are shown in Table 2 (http://www. rgz.gov.rs). Transformation grids are also publicly available, but only with the special approval of RGA. It must be pointed that coordinate differences between the two epochs are treated as insignificant, so it can be said that ITRF96 at epoch 1998.7 and ETRF2000 at epoch 2010.63 can be considered to be equivalent for the purpose of transformation parameters estimation. Significant residuals along all three coordinate axes were noted after the transformation into coordinates related to SRB_ETRF89. Horizontal position residuals range from + 2 to −2 m (Fig. 13), while height residuals are two to three times greater. A further two grids were created to eliminate the effects of the remaining residuals when using AGROS in every day work. These grids are often called transformation grids, for both axes, i.e. a grid for residuals along the geodetic latitude and a grid for residuals along the geodetic longitude. Entering data for grid creation was represented by residuals along the corresponding axis. A grid resolution of 1 kilometre × 1 kilometre was adopted. Residual of horizontal residuals Geoid RGA started an initiative in 2001 to collect data for the determination of a geoid model, i.e. quasigeoid model for Serbia. A large amount of detailed gravimetric survey data were gathered from a number of institutions in Serbia. The total amount of data gathered between 2001 and 2007 resulted in over 80,000 gravity points, i.e. on average one point per square kilometre. The Military Geographic Institute of Serbia created a Digital Terrain Model (DTM) between 2001 and 2004 for Serbia with a resolution of 1 arc second in both directions. This DTM was made available to RGA to be used for the determination of geoid, i.e. quasigeoid model. The RGA itself gathered over 1000 discrete height anomaly values, i.e. undulations between 2001 and 2007. A database was created using all available data for the modelling of the geoid/quasigeoid surface. A preliminary geoid for Serbia was completed in 2008, which enabled ellipsoid heights to be transformed with the precision of 5 centimetres for Survey Review 2016 9 Odalović et al. Chronology of the development of geodetic reference networks in Serbia 14 Schematic representation of AGROS usage: a without any transformation, b transformation of archive data into new reference frame 95% for territory of Serbia (Odalović , 2008). After determining the preliminary geoid, the first official quasigeoid which originated within the mutual project of RGA and Swedish International Development Cooperation Agency (SIDA) was created in 2011 (Ägren et al., 2011). According to the technical reports, the resulting quasigeoid attained precision of several centimetres for the whole territory of Serbia. AGROS application Wherever possible, AGROS is used exclusively for positioning in Serbia today. Ellipsoid heights are transformed into normal heights using the 2011 quasigeoid model in combination with the relation HN = h − z (3) where H is the normal height, h is the ellipsoid height that results directly from GNSS survey and z is the height anomaly that results from the 2011 quasigeoid solution. Normal heights are obtained using (3) as shown in Fig 14a and b. N Conclusion and future activities In this paper, the chronological summary of the establishment and development of geodetic networks in Serbia is given. The period from the mid-nineteenth century until modern day is included. It can be said that the quality of the geodetic networks was influenced by available equipment and the development of different positioning techniques and certain political conditions. The first work on establishing trigonometric networks in Serbia was based on terrestrial survey techniques and was connected to the Austro-Hungarian monarchy. At that time, the monarchy established the first-order trigonometric network not only in Serbia, but also in other countries of Western Balkans which were being under 10 Survey Review 2016 the Ottoman Empire. After becoming independent and establishing the Kingdom of Serbia, further works on the development of the trigonometric network in contemporary Serbia, Macedonia and Montenegro were being performed, but this work was stopped during the First World War. The network was finally completed in 1923. Network densification was continued from after the Second World War until 1996. The network development and maintenance came to a standstill between 1974 and 1996. Economic conditions, frequent border alterations and territorial organisation changes have had, as a consequence, resulted in an inadequate trigonometric network. The same can be said about levelling networks. With the introduction of GNSS and its mass usage in the beginning of the 1990s, GNSS positioning techniques took priority over terrestrial techniques for two-dimensional (horizontal) positioning. So, the work to establish a passive reference network using GNSS was started in 1996 together with the establishment of network of permanent stations in Serbia – AGROS, which today represents the main base for positioning. At the same time, several European campaigns were realised which include the Republic of Serbia and surrounding countries in the European reference network. Today, the main task is to solve the question of integration of data obtained using AGROS with data obtained by terrestrial techniques based on the old reference system. It is necessary, therefore, to collect as many points as possible, so that any deformation of the Earth’s crust that may have arisen during the last 150 years can be described, for the creation of future transformation grids. Acknowledgements This work was supported by the Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja [grant number 36020]. Odalović et al. ORCID http://orcid.org/0000-0001-6004-824X Oleg Odalović http://orcid.org/0000-0002Miljana Todorović Drakul 8782-0890 http://orcid.org/0000-0002-2533-1100 Sanja Grekulović http://orcid.org/0000-0003-0479-2538 Jovan Popović http://orcid.org/0000-0002-4158Danilo Joksimović 0000 References Ägren, J., Djalovic, S., and Skrgunj, J., 2011. Plan for the future determination of a national geoid model for Serbia. Belgrade, Serbia: Republic Geodetic Authority, Tech. rep. 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Kent: Abacus Press. Mugnier, C. J., 1997. Grids & datums – Yugoslavia. Photogrammetric Engineering & Remote Sensing, 63, 1042–1062. Odalović , O., 2008. Preliminary geoid for Serbia. Belgrade, Serbia: Republic Geodetic Authority, Tech. rep. Odalović , O., Milenković , V., and Aleksić , I., 2010. AGROS: Present status and the future activities, IV Croatian Congress of real estate cadastre. Popović , J., 2010. Active geodesy reference base application in real-estate survey (in Serbian), Master thesis. Faculty of Civil Engineering, Department of Geodesy and Geoinformatics, University of Beograd. Timar, G., 2007. The Ferro prime meridian. Geodezia es Kartografia, 59 (12), 3–7. Veljković , Z. and Lazić , S., 2011. EUREF Serbia 2010 final report, republic geodetic authority of Republic of Serbia, 2011, Moldova. Survey Review 2016 11