The International Terrestrial Reference System (ITRS) is realized by geodetic space techniques, which are linked by local-ties at the observation stations. Therefore, reliability and high accuracy are the main requirements for the determination of the different reference points in the corresponding local reference frame. At the Geodetic Institute of the University of Karlsruhe several scientific studies have been carried out to determine the reference point of radio telescopes at different observation stations and with different calculation models. Starting in 2002 the IVS reference point at Onsala Space Observatory was determined by 3D-circle fits with error propagation using full covariance information, which is custom procedure nowadays. In 2008 a completely new mathematical model was established able to fulfill future requirements as for example minimizing downtime of the telescope. Geodetic measurements with a tacheometer respectively a lasertracker at the Fundamentalstation Wettzell and the Onsala Space Observatory yielded a good verification of the model.
This contribution shows the evolution and obtained expertise in reference point determination at the Geodetic Institute of the University of Karlsruhe by comparing the results of different campaigns at the Onsala Space Observatory.