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Figure 1 Model of the reference surface [2]. h is ellipsoidal height, H is orthometric height and N is geoid undulation

Figure 1 Model of the reference surface [2]. h is ellipsoidal height, H is orthometric height and N is geoid undulation

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Figure 2 The different surfaces and their heights [6].
Figure 2 The different surfaces and their heights [6].
The system includes at least ‘twenty-four satellites that orbit the earth at a height of 20,200 km and inclined 55 from the equator. Three satellites are enough to solve for any position [6]. The coordinates of GPS are on a Cartesian system (X-Y-Z) having the same origin as the WGS84 ellipsoid. WGS84 geocentric Cartesian system (X-Y-Z) can easily be converted into WGS84 ellipsoid coordinate's geodetic latitude, geodetic longitude and height of ellipsoid, see Fig. 4.
The system includes at least ‘twenty-four satellites that orbit the earth at a height of 20,200 km and inclined 55 from the equator. Three satellites are enough to solve for any position [6]. The coordinates of GPS are on a Cartesian system (X-Y-Z) having the same origin as the WGS84 ellipsoid. WGS84 geocentric Cartesian system (X-Y-Z) can easily be converted into WGS84 ellipsoid coordinate's geodetic latitude, geodetic longitude and height of ellipsoid, see Fig. 4.
Figure 5 Principles the geometric trilateration of GPS [6].
Figure 5 Principles the geometric trilateration of GPS [6].
Figure 6 Satellite Image of The Study Area (Google), 2016. The Baghdad University campus at Al-Jaderiyais the area of this study, see Fig. 6.Orthometric and Ellipsoidal heights for selected Control Points are observed accurately with Nikon Total Station (Nivo 5C) and Garmin GPS (map 78S) respectively. Geoid Undulation or the Geoidal height (N) for the Control Points can be calculated by using two different methods to compare between them, one of these was Geoid Model (EGM) method and the other was the difference between heights.
Figure 6 Satellite Image of The Study Area (Google), 2016. The Baghdad University campus at Al-Jaderiyais the area of this study, see Fig. 6.Orthometric and Ellipsoidal heights for selected Control Points are observed accurately with Nikon Total Station (Nivo 5C) and Garmin GPS (map 78S) respectively. Geoid Undulation or the Geoidal height (N) for the Control Points can be calculated by using two different methods to compare between them, one of these was Geoid Model (EGM) method and the other was the difference between heights.
Table1 Total station and GPS observations for the ground control points There are some differences in the results between total station and GPS observations because of each of that are acquired depend on the different datum. GPS provide ellipsoid heights, while the total station heights are based on a level surface called the geoid (M.S.L).The results in Table .1 represent a part of GCPs which are observed by using Total Station and GPS. The total number of these points was thirty- eight pointsdistributed in the site.Fig.8shows the whole points distributed along the survey line against heights.
Table1 Total station and GPS observations for the ground control points There are some differences in the results between total station and GPS observations because of each of that are acquired depend on the different datum. GPS provide ellipsoid heights, while the total station heights are based on a level surface called the geoid (M.S.L).The results in Table .1 represent a part of GCPs which are observed by using Total Station and GPS. The total number of these points was thirty- eight pointsdistributed in the site.Fig.8shows the whole points distributed along the survey line against heights.
Figure 7Orthometric and ellipsoid height 2.4. EGM 2008 Computation Method
Figure 7Orthometric and ellipsoid height 2.4. EGM 2008 Computation Method
Figure 8 Comparison between the orthometric and ellipsoid height.
Figure 8 Comparison between the orthometric and ellipsoid height.
Baghdad University Compus with Selected GCPs
Baghdad University Compus with Selected GCPs
Table 2Geoid undulation (N) computed by using (H-h) method and EGM 2008 model.
Table 2Geoid undulation (N) computed by using (H-h) method and EGM 2008 model.
Figure 11 Undulation or geoid height at each point using (h-H method) Fig. 11 and Fig. 12 are statistic figures that declare the relationship between points distributed along the survey line against the Geoid undulation by using the two different methods respectively. It can be noticed that, the EGM 2008 is the regular geometrical model which used to the local geodetic dataset.
Figure 11 Undulation or geoid height at each point using (h-H method) Fig. 11 and Fig. 12 are statistic figures that declare the relationship between points distributed along the survey line against the Geoid undulation by using the two different methods respectively. It can be noticed that, the EGM 2008 is the regular geometrical model which used to the local geodetic dataset.
Table 3 The comparison between (N) and (N ') and the differences between them.
Table 3 The comparison between (N) and (N ') and the differences between them.
Maximum and the minimum values for the Geoid Undulation are (1.6261 m), and (1.5964 m) respectively with average (1.61 meter) by using (EGM 2008). When it is used the difference method (h-H), maximum and the minimum values for the Geoid Undulation are (5 m), and (2 m) respectively. Finally, the model EGM-2008 represents the best method to determine the Geoid Undulation. dN value between the two different methods is a maximum (3.40) m, a minimum (0.40 m), the average value (1.5 m), and a standard deviation (SD)= +0.030. At last, image map was produced using Arc GIS 10.1.
Maximum and the minimum values for the Geoid Undulation are (1.6261 m), and (1.5964 m) respectively with average (1.61 meter) by using (EGM 2008). When it is used the difference method (h-H), maximum and the minimum values for the Geoid Undulation are (5 m), and (2 m) respectively. Finally, the model EGM-2008 represents the best method to determine the Geoid Undulation. dN value between the two different methods is a maximum (3.40) m, a minimum (0.40 m), the average value (1.5 m), and a standard deviation (SD)= +0.030. At last, image map was produced using Arc GIS 10.1.
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