COORDINATE TRANSFORMATION FROM KARBALA 1979 AND WORLD GEODETIC SYSTEM 1984 TO IRAQI GEOSPATIAL REFERENCE SYSTEM

: Nowadays, the transformation between coordinate systems is the major interested problems especially in Iraq. There are many coordinate systems used to produce maps and documentations due to different datums and spheroids. These coordinate systems are preferable to be unified in local countries. Thus, this paper deals with the transformation of coordinate systems of Karbala 1979 Polservice and World Geodetic System (WGS) 1984 to Iraqi Geospatial Reference System (IGRS). Accurate and well distributed control points are selected to cover the study area in Baghdad city, Iraq. Coordinate transformations are implemented using ArcGIS application mainly. Also, MATLAB software is used to convert geographic to map coordinates and vice versa by designing two MATLAB programs. The differences between the coordinate systems have been calculated. The results found that the discrepancies between Karbala 1979 Polservice and IGRS are about 278.6 m, -287.6 m, 0.01 second, and -11.2 second in northing, easting, latitude, and longitude, respectively. The WGS 1984 is superposed to IGRS and the distinction between them is negligible. The map coordinate differences between ArcGIS and MATLAB results are about -16 to 14 mm in northing and about -13 to 12 mm in easting, while the latitude and longitude differences are zero.


Introduction
The geodetic networks in Iraq have been passed through different stages. The progression of these networks includes Nahrwan 1934, Nahrwan 1967, Karbala 1979 Polservice, and the modern geodetic network of Iraqi Geospatial Reference System (IGRS). Geodetic networks consist of many control points defined by a datum and a spheroid. Table 1 illustrates the geodetic datums and spheroids used in Iraq. A datum provides a frame of reference for measuring locations on the surface of the earth [1]. The geodetic networks of Nahrwan 1934 and Nahrwan 1967 which have been established by British are called the English networks. These networks are based on Clarke 1880 Royal Geographical Society (RGS) spheroid. All English networks as well as the gravity points are almost completely extinct [2]. The geodetic network of Karbala 1979 Polservice was established by Polish State Enterprise for geodesy and cartography based on Karbala 1979 Polservice datum and Clarke 1880 RGS spheroid. The Iraqi geodetic control networks established by British and Polish are limited, destroyed, and their data documentations are difficult to obtain.
The American Institution of National Geodetic Survey (NGS) developed the geodetic network in Iraq called the IGRS during the period between (2004) to (2005). The control surveys of IGRS are based on Global Positioning System (GPS). The default GPS observations are based on World Geodetic System 1984(WGS 1984 datum and ellipsoid. Also, the WGS 1984 with Earth Gravitational Model (EGM 1996or EGM 2008 is the vertical datum used in GPS receivers [3]. IGRS is a series of six GPS Continuously Operating Reference Stations (CORS) which are spread geographically throughout the Iraq country [4]. The origin of IGRS is the International Terrestrial Reference Frame (ITRF2000) at epoch (1997.0). The original IGRS established in 2005 comprised six CORS and sixty-four High Accuracy Reference Network (HARN) points levelled in six southern provinces in Iraq [5]. Iraqi Ministry of Water Resource, State Commission on Survey installed seven CORS stations and continued establishing the HARN points for whole Iraq provinces [6]. HARN points have been established relative to the CORS network forming the IGRS control network [6]. HARN is like a first order survey control network, while IGRS is a three dimensional coordinate system. Nevertheless, up to the current IGRS, which was established with the help of the US and British Armies, the geographic coordinate reference systems were two dimensional, i.e. they excluded height information [7]. In most works, the geographic coordinates are measured and then transformed to map coordinates [8]. Universal Transverse Mercator (UTM) map projection is used for obtaining map coordinates. Each UTM zone has a false northing in the northern hemisphere: (0 m) and a false easting for every zone: (500000 m) [9]. A translational shift must be applied to convert coordinates from one datum to another. This situation is further complicated because the horizontal shifts are different for graticule and grid coordinates [10].

Study Objective and Software Used
The main objective of this study is to convert the commonly used coordinate systems in Iraq (karbala 1979 Polservice andWGS 1984) to IGRS using ArcGIS Desktop 10.8, and then develop equations that can be used to convert the karbala 1979 Polservice geographic and map coordinate systems to IGRS and vice versa within the study area. The coordinate transformations are done with the Project tool in ArcGIS software. In addition, two MATLAB programs are built using MATLAB software version 7.8.0.347 (R2009a) to convert the geographic coordinates to map coordinates and vice versa. The satellite image and control points are obtained from google earth pro 7.1.8.3036 build date 2017.

Study Area and Data Collection
The study area is placed in Baghdad city along the river of Tigris in Iraq. It is expanded from (33° 10′ 50″ N) to (33° 26′ 40″ N) latitude and from (44° 08ʹ 00″ E) to (44° 36′ 50″ E) longitude. The study area has been chosen because Baghdad city is the capital of Iraq and it meets the requirement of the research that represented by  WGS 1984WGS 1984GRS 1980 the possibility of reconnaissance the locations of points in the field. Fig.1 shows the location of Baghdad city on the map of Iraq and exhibits Baghdad map as well as the chosen control points (CPs). The map scale on the computer display is (1:250000) as shown in Fig.1. Twenty control points are scattered and distributed covering the whole region. The original data of satellite image and control points have been obtained from the google earth pro. The coordinate system of these data is according to WGS 1984 datum and spheroid. This coordinate system has been modified to IGRS datum and GRS 1980 spheroid using ArcGIS application.

Design of MATLAB Programs for Coordinate Transformations
Coordinate transformations are implemented by designing two MATLAB programs. The first program is used for the transformation of geographic coordinates [Latitude (Phi) and Longitude (Lambda)] to map coordinates [Northing (N) and Easting (E)] as shown in Fig.  2, while the second program is used for the inverse transformation of map coordinates to geographic coordinates as shown in Fig. 3. The adopted transformation equations are found in Snyder [11]. The designed programs are listed in Appendix-A.

Implementation and Results
The commonly available three coordinate systems in Iraq are Karbala 1979 Polservice, WGS 1984, andIGRS. The spheroidal parameters differences between Karbala 1979 Polservice and IGRS datum and between WGS 1984 and IGRS datum are calculated in Table 2 and Table 3, respectively. The source data include satellite image and twenty control points obtained from google earth pro. These data are based on the geographic coordinate system of WGS 1984.   0.01 second and −11.2 second, respectively, in the study area.
The transformations between the coordinate systems have been implemented using the Project tool in ArcGIS. Also, the Project tool has been used to convert between geographic and map coordinate systems. The geographic coordinates of Karbala 1979 Polservice datum with Clarke 1880 RGS spheroid, WGS 1984 datum with WGS 1984 spheroid, and IGRS datum with GRS 1980 spheroid are projected to UTM zone 38 north. The map coordinates of Karbala 1979 Polservice and IGRS are listed in Tables 5(a) and 5(b), respectively, while the northing differences (DN) and easting differences (DE) between these two coordinate systems are listed in Table 5(c). On the other hand, the first program designed by MATLAB is used to transform the geographic coordinates obtained by ArcGIS to map coordinates. The resulted Karbala 1979 Polservice and IGRS map coordinates are listed in Tables 6(a) and 6(b), respectively, while the differences between these two coordinate systems are listed in Table 6(c). The results of using ArcGIS and MATLAB show that the mean of northing and easting differences between Karbala 1979 Polservice and IGRS coordinate systems are about 278.6 m and −287.6 m, respectively, in the study area. Also, the second program designed by MATLAB is used to convert the map coordinates to geographic coordinates. The resulted geographic coordinates coincide with ArcGIS results.  Figure 4, Figure 5, Figure 6 and Figure 7 show latitude, longitude, northing and easing differences between Karbala 1979 Polservice and IGRS coordinate systems, respectively.
For both Karbala 1979 Polservice and IGRS, the map coordinate differences between ArcGIS and MATLAB results are about (− 16 mm to 14 mm) in northing and about (− 13 mm to 12 mm) in easting as represented in Figure 8, Figure 9, Figure 10, and Figure 11. The latitude differences and longitude differences between ArcGIS and MATLAB results are equal to zero. In addition, the WGS 1984 is approximately superposed to IGRS and the distinctions between them are negligible within the accuracy limits of coordinate conversion.

Conclusions
The following findings can be concluded:    Figure 11. IGRS easting differences between ArcGIS and MATLAB results differences between ArcGIS and MATLAB results are equal to zero.

Recommendation
There are different coordinate systems used in Iraq resulted from different geodetic networks. Some of these geodetic networks such as Nahrwan 1934 and Nahrwan 1967 are completely cancelled in Iraq. Others like Karbala 1979 Polservice network is still used in some projects. The user should take into account coordinate discrepancies before the work. Up to date, some of available maps and documents in Iraq offices and departments have been printed in Karbala 1979 Polservice with Clarke 1880 RGS coordinate system. These maps must be updated and adopted a uniform coordinate system such as IGRS.