Evaluation procedure for coordinate transformation

With the use of the global positioning system, World Geodetic System 1984 (WGS84) [or The International Terrestrial Reference Frame (ITRF)] has been widely accepted as a global geodetic reference system and adopted by many international and national organizations (e.g.. the International Civil Aviation Organization and the International Maritime Organization). However, most existing maps are based on different local datums (i.e., UK OS36 and HK80 datums). The transformation of station coordinates between WGS84 and local datums is frequently required. Because of the distortions of the existing classical geodetic network, it is impossible to develop one transformation that is optimal for all cases. Various algorithms have been developed for the transformation between different reference frames. Therefore, the selection of a transformation for a specific geodetic network has to be evaluated case by case. In this paper, a simple procedure is proposed to evaluate the performance of a transformation, based on several predefined quality indicators, such as precision, invertability, uniqueness, conformality, and extensibility. As an example, the performances of three different transformations are evaluated for the transformation between the Ireland mapping datum (Ireland 1975) and the European Terrestrial Reference Frame 1989 (ETRF89), using the quality indicators proposed in this paper.