CROATIAN HEIGHT TRANSFORMATION MODEL

Abstract

After 1991, when the Republic of Croatia became independent, the “old” height reference system (HVRS1875) from the former Yugoslavia was still officially used. Soon the process of restoration and enhancement of geodetic datums and reference coordinate systems was initiated and in 2004, this resulted in the realisation of a new height reference system (HVRS71). In order to ensure the continuity of height data use along with an efficient height coordinates transformation between the two reference systems, the Croatian height transformation model (HTMV) was created. The model is based on height data of geometric levelling benchmarks of all levelling orders of accuracy, which are located on the Croatian territory, and which are included in both height reference systems. The HMTV was created on the basis of mutually independent modelling of datum and distortion components which are both comprised by the differences of the benchmarks' height coordinates. The model's datum component is a result of different height datums in the old (HVRS1875) and the new (HVRS71) height reference system. The referent height surfaces, realised by these datums, have different spatial orientation in respect to the Earth's body and are not mutually parallel. The model's distortion component is a result of different adjustment methods and procedures used to determine absolute benchmark heights and different geometric configurations of levelling lines and networks. Furthermore, it should be pointed out that levelling data from different time epochs were combined. The model's datum and distortion component were successfully integrated into a unique grid transformation model. The HMTV is a high accuracy transformation model, based on a homogenous density grid, meeting the criteria of efficiency, unambiguity and simplicity.