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Levelling is the usual technique used to determine difference in height between ground points. Nowadays Global Positioning System (GPS) provides a quick modern technology to determine this difference. Because the datum surfaces are different in both techniques, different results may be expected. In this research work, difference in heights between numbers of points, in Khartoum State, were carried out using both ordinary levelling (in which Geoid is the reference datum) and GPS techniques (in which Ellipsoid is the reference datum). Results obtained showed that GPS data can be used directly to produce contour map up to 1:100,000 map scale with 25m interval. Results also assisted to determine the Geoid undulation in the area.
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