BALTIC QGEOID COMPUTATION AS HEIGHT COMPONENT OF THE GEODETIC INFRASTRUCTURE FOR GNSS POSITIONING SERVICES IN THE BALTIC STATES Reiner Jäger 1) , Janis Kaminskis 2) , Janis Balodis 3) , Janis Strauhmanis 2) and Ghadi Younis 1) 1) Faculty of Geomatics, Karlruhe University of Applied Sciences. Moltkestrasse 30, D-76133 Karlsruhe, Germany 2) Faculty of Civil Engineering, Riga Technical University (RTU). Azenes Iela 16/20 – 238A, Riga, LV-1048, Latvia 3) Institute of Geodesy and Geoinformation, University of Latvia, Riga. 19 Raina Blvd., Riga, LV–1586, Latvia The worldwide ongoing process of the establishment of high precise regional GNSS-positioning services (e.g. LATPOS), which are con- sistent to ITRF-related frames, leads to the new age of GNSS-posi- tioning. The process is further promoted by an increasing number of GNSS orbital segments as well as high precise global GNSS-services. So GNSS becomes an interdisciplinary tool with a broad spectrum, re- lated to precise positioning, precise navigation, robotics, mobile GIS and mobile IT applications. The determination of physical heights H by the transformation H=h-N of the ellipsoidal GNSS heights h to the Geoid or QGeoid height reference surface N as 2 nd component of the geodetic infrastructure for GNSS positioning services (GIPS), requires the computation of Geoid- or QGeoid-models N, and belonging RTCM capable databases, as a sustainable geodetic task in the establishment of GIPS. After an overview about the different GIPS components and the realization of concepts and software for all four different GIPS components, which have been developed in international cooperations and projects, the main target of the contribution is to present in detail the mathematical models of the general world-wide valid concept for the computation of height reference surfaces (HRS), namely geoid or quasi geoid (QGeoid) models N as essential part of GIPS. The concept is shown at the computation of the Baltic QGEoid over the territories of Estonia, Latvia an Lithuania. The computation was done in the frame of a research cooperation between the Riga Technical University (RTU), the University of Latvia and Karlsruhe University of Applied Sciences (HSKA), using the DFHRS-software developed at HSKA. Key Words Geodetic Infrastructures for GNSS-positioning Services (GIPS), Q-Geoid Compu- tation, Spherical Cap Harmonics, EGG97, EGM2008, Vertical Deflections, Gravity Data, RTCM-Transformation Messages 1. Geodetic Infrastructures for GNSS-Positioning Services (GIPS) To enable the full spectrum of GNSS usability, the establishment and maintenance of a respective geodetic infrastructure for GNSS positioning services and applica-