## 5 Conclusions  
The results of dynamic response measurements using two different methods--RTSs and SLDV--show that geodetic methods are suitable for monitoring the dynamic response of structures subjected to vibration. Despite the higher number of readings, the problem of sampling uniformity may still arise. By excluding the distance meter, more uniform readings can be obtained. When determining the dynamic response, it is sufficient to only capture the variation along the angular directions.  
When using RTSs to monitor the dynamic response of a structure, it is important to incorporate conventional physical methods into the monitoring. In this way, sufficient accuracy and visibility for changes in physical quantities that cannot be measured by geodetic methods can be ensured.  
In order to compare the results obtained by geodetic and physical methods, it is necessary to transform the geodetic results. This can be achieved using spectral analysis methods, such as the fast Fourier transform and the Lomb-Scargle algorithm, which were proven to be appropriate mathematical tools for the analysis and processing of the measured signals. Using the Lomb-Scargle algorithm, we were also able to check the consistency of the original signals in the case of the geodetic methods by means of a spectral approximation in the range from 0 to 1 Hz. Furthermore, in the case of the physical methods, we were able to conclude that the spectral analysis provided extremely important information about the measured signals, such as the dominant frequency and the corresponding amplitude. Spectral analysis was thus proven to be a good mathematical tool for advanced data processing when comparing data.  
The limitations of the presented model for monitoring the dynamic response of railway sleepers arise mainly when using contact methods on bridging facilities. If we want to monitor the response in a bridging object, it is necessary to provide an additional structure that is not tied to the observed object, since we have to install equipment on it to determine the responses of the observed object. Placing an additional structure--in the sense of construction scaffolding--is, of course, a problem for tall buildings, for inaccessible terrain under a building and, of course, for greater distances. The problem with the described measurement using the LDV equipment was also the range, as we were limited to maximum of 30 m. That is why we were looking for a solution to these problems and used a non-contact geodetic method, which can be used practically everywhere and at great distances and ranges. The method also has an advantage, as it provides the results for vertical movements in real time. Of course, this method also has its limitations, which mainly manifest in uneven and insufficient numbers of samples, presenting a problem in the calculation of the dynamic response. The overall conclusion is that the limits of the use of geodetic sensors for monitoring engineering structures have been greatly expanded, opening up new horizons in the monitoring of the condition of these structures during their service life.  
Conceptualization, B.K., S.T., R.P. and S.L.; methodology, B.K. and S.L.; software, B.K. and S.L.; validation, B.K., S.T., R.P. and S.L.; formal analysis, B.K. and S.L.; investigation, B.K., S.T., R.P. and S.L.; resources, B.K. and S.L.; data curation, B.K., S.T., R.P. and S.L.; writing--original draft preparation, B.K. and S.L.; writing--review and editing, B.K., S.T., R.P. and S.L.; visualization, B.K. and S.L.; supervision, B.K. and S.L.; project administration, S.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.