## 1 Introduction
For relative models, leveling measurements are often used in combination with measurements on tide gauges as well as GNSS. Due to the way it is developed, this group also includes data acquired from Synthetic Aperture Radar (SAR) [7]. The vertical crustal movements absolute models are mainly based on GNSS data [8,9]. The vertical movements determined from GNSS data mainly depend on the duration of station operation, the way the data are processed [10] (e.g., Precise Point Positioning--PPP or double difference), and the methods adopted for time series analysis and trend determination, e.g., noise analysis [11], detecting offsets [12], and seasonal signals [13]. Permanent GNSS stations are not linked to each other by a fixed network structure and the distances between them range from a few up to almost a hundred kilometers. This may cause the vertical movements determined on them to show local or own station movements. The quality of leveling data is more predictable and depends mainly on the measurement technique adopted (usually precision leveling), which makes it possible to limit the influence of local ground deformations. The length of operation of permanent stations currently allows vertical movements to be determined with an accuracy comparable to that of those determined from leveling data. Merging these collections will allow for verification of the local nature of vertical movement at GNSS stations and increase the spatial resolution of the data. It is not only sets based on different measurement methods that can be combined but also sets of the same type but differing in processing, coverage and measurement epochs. Different approaches to this topic can be found in the literature [10]. The predominant methods are mainly based on a statistical-mathematical approach: velocity averaging, network (joint adjustment of several networks of vertical motions based on, for example, a triple or quadruple leveling network) [11], transformation [12] and interpolation (if the data used are developed as relative motions to the same datum) [13]. Tables 1 and 2 summarize the advantages and disadvantages of individual methods of modeling vertical movements of the Earth's crust. The selection of connections between GNSS stations can take place in any way. In [6], the connections were formed from one point (GNSS stations) to the others. In other work [14], GNSS stations were connected in a network structure based on the Delaunay triangulation algorithm, where the observations are vertical movements between GNSS stations constituting the vertices of the triangles. In [15], stations were connected into triangles based on criteria such as the closest location between the combined stations and the normal geometry condition. To perform the transformation process or simultaneously align two or more vertical motion networks from leveling, GNSS or other geodetic data, it is also necessary to define combined points. In [3,16], some general principles as to their location were indicated, while [17,18] present how to select relevant common points in hybrid networks based on the scale-free network theory using the example of the European leveling network (UELN) and the European GNSS permanent station network (EPN) [19,20, 21]. GNSS stations and leveling benchmarks are generally not physically the same points. Vertical tectonic deformations are usually characterized by a slow linear trend of subsidence or uplift, while seismically active regions may experience sudden changes (or events) in vertical movements [22]. If vertical deformation only concerns tectonics, tectonic movements should have similar movements for individual tectonic blocks [23]. It should then be assumed that two (or more) measured points are some distance apart (distance criterion) but are a single point (pseudo-nodal point) [18]. This study showed that for a hybrid network based on UELN and EPN points, up to 90% of the points are pseudo-nodal points. The determination of the distance criterion is arbitrary.