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One of the important contents to achieve the goal of modernization of the height system is connect the levelling observations between national levelling order I, II to the national GNSS Continuous Operating Reference Stations and the national gravity marks. Today, Vietnamese surveyors commonly use Geoid model 2010 that built based on more than 3000 gravity marks and over 800 GPS-levelling points. The processing combined GNSS-levelling and gravity obervations to improve the Geoid model for archiving accuracy from 4 to 10 centimeters, that can be possible to apply topographic heigh using GNSS accurately instead of traditional levelling is necessary for geomatics and mapping in Vietnam. There are some researchs in the literature aim to improving geoid model. In these research, the interpolation methods are mainly discussed such as collocation, linear function order 1, 2 or spline function. In this paper, the objective is to consider and propose a method of data processing using theothy of adjustment with contrainned codition and analyze the covariance matrix of the input data.

Application of adjustment with contrainned codition in mixed GNSS, levelling control network and improving accuracy of the Geoid model