International Journal of Computational Engineering Research||Vol, 03||Issue, 4|| www.ijceronline.com ||April||2013|| Page 52 Geoidal Map and Three Dimension Surface Model Part of Port Harcourt Metropolis from “Satlevel” Collocation Model Olaleye J. B. 1 , J. O. Olusina 1 , O. T. Badejo 1 and K. F. Aleem 2, 3 1 Department of Surveying and Geoinformatics, University of Lagos. Akoka - Lagos, Nigeria 2 Department of Geomatics Engineering Technology, Yanbu Industrial College, Yanbu Industrial City, Saudi Arabia 3 Surveying and Geoinformatics Programme, Abubakar Tafawa Balewa University, Bauchi Nigeria I. INTRODUCTION 1.1 Geoidal Map: Geoidal map is similar to contour map which is made up of contour while geoidal map is made up of geoidal lines depicting the value of geoid for any points on the earth‟s surface. Three dimension surface models show the three dimension configuration of the area. The heights of points above the Mean Sea Level (MSL) are used for producing contour map, while geoidal values at different points are used for producing the geoidal map. It is also with reference to the geoid approximated by Mean Sea Level. Therefore, any line on a geoidal surface is an imaginary line drawn on the geoidal map to connect points of the same geoidal height value on, above or below the earth surface. The accuracy required for such maps necessitates the knowledge of the accurate and precise determination of the geoid at the same area. (Amin et al, 2005) 1.2. Geoid The geoid is the surface which coincides with that surface to which the oceans would conform over the entire earth, if free to adjust to the combined effects of the earth's mass attraction (gravitation) and the centrifugal force of the Earth's rotation. Specifically, it is an equipotential surface, meaning that it is a surface on which the gravitational potential energy has the same value everywhere with respect to gravity. The geoid surface is irregular, but considerably smoother than earth's physical surface. Sea level, if undisturbed by tides, currents and weather, would assume a surface equal to the geoid, when the observation is carried out for a numbers of years, usually 18.61years. (Deakin, 1996, Olaleye et al, 2010; Aleem, 2013) Determination of the geoid has been one of major challenges of geodesists. Gravity data have been used in the past with stokes integration and other approaches. One of such conventional methods was used by Hirvonen (1934) to carry out the first computation on a worldwide scale. He computed the geoidal undulation for 62 points distributed in an East –West band encircling the entire earth surface. For the first time, mean free air anomalies were estimated from the available gravity data covering 5˚ by 5˚ blocks. Also, Tanni (1948 and 1949) used large quantity of gravity data to compute the global geoidal heights. He employed the Prat-Hayford system‟s gravity reduction method and Airy Heiskanen system. He later computed the global geoidal undulation Abstract: Geoidal map depicts the geoid configuration of the area under study. Data acquisition for the production of such maps has been very tedious, time consuming and expensive with the use of classical and conventional geoid determination methods. "Satlevel" Collocation is a new method of geoid determination in which the ellipsoidal height from any satellite based system is combined with orthometric height from geodetic levelling to model the geoid. The method enables the geoid to be determined in patches. Geoid so determined can be applied with ellipsoidal height to get orthometric height which height users always prefer. In this work, "Satlevel" Collocation model along with the user‟s interactive computer program “Orthometric Height on Fly”, were used to generate geoidal values in part of Port Harcourt metropolis. The generated data was used to produce the Geoidal map of the study area using SURFER software. The map was overlaid on the Local government map of Rivers State of Nigeria. The production of Geoidal map from "Satlevel" Collocation is easier than the conventional methods, when the initial geoidal coefficients have been determined. This method can be extended to other parts of Nigeria and the world at large. Keywords: Geoid, Geoidal Map, Geoid Modelling, “Satlevel‟ Collocation, Three Dimension Surface and SURFER