Local Geoid Model Generation Using the Geometrical Approach

摘要

The global navigation satellite systems(GNSS)provide an accurate three-dimensional positioning including the geodetic(ellipsoidal)height(h),which is,in most cases,must be transformed to the local/regional orthometric height(H)to have physically the desired meaning of the elevation above the national vertical datum(e.g.,MSL(Mean Sea Level)).Usually,the local orthometric heights are determined based on the value of geoid undulation(N),which is obtained by methods of gravimetrical observations or derived by methods of interpolation utilizing the local geoid models(LGM).The current paper highlights one of the methods of generating LGM that is based on the geometrical relationship between the global datum WGS84 and the Iraqi datum Karbala 1979.The DGPS(Differential GPS)method is used to get the geodetic coordinates of about 97 selected points to cover the experimental area,within the boundaries of Erbil municipality,which has been partitioned into four parts.Therefore,four LGM were generated individually for each one of the four parts with an estimated uncertainty equal to±0.076 m.