The real-time frames may develop a need for data originating from the concrete reference system. Sometimes this can refer to the Gauss-Krüger coordinates and UTM projections with a specific date. This paper analyses the connection between UTM projection with date WGS-1984 and Gauss-Krüger coordinates for a wider area of the City of Rijeka, without a precise need for making the reference to the specific reference coordinating system. Paper also includes the observations of mathematical frames which define Helmert transformations as tool which enables switching from one to another reference system. Additionally, it discusses the needs and possibilities of described tool within GIS and GPS navigation and possibilities of computer programmes which can modularly be implemented into the specialized programmes for Geodesic purposes.