Numerical modeling of gravitational field lines - the effect of mass attraction on horizontal coordinates

There are two basic types of geodetic projections by which the points locat ed on the Earth's surface can be projected onto a reference ellipsoid. Beca use of the different principles of Helmert's and Pizzetti's methods two set s of horizontal and vertical coordinates are obtained for the same set of s urface points. The difference is investigated in terms of offsets of horizo ntal coordinates. For an estimation of the offsets the field lines going th rough topographic masses are determined by three different numerical method s in 'flat Earth approximation' using a volume element model of the density distribution of the lithosphere in a part of central Europe. The maximum h orizontal offset reaches 20 cm on the investigated area at the level of the geoid.