The DFHRS research project of the Hochschule Karlsruhe - University of Applied Sciences (HSKA) aims at the parametric modelling and computation of height reference surfaces (HRS) from geometric and physical observation components in a hybrid adjustment approach (DFHRS). The access to the parametric HRS model is enabled by DFHRS data-bases, which allow the direct conversion of GNSS-heights h into physical standard heights H. DFHRS data-bases are used for online GNSS-heighting in DGNSS-networks (SAPOS, ASCOS etc.) and in GIS, and have been computed for different states in Germany as well as several nations and regions in Europe, Africa and USA.