High industrial chimney inclination monitoring and analysis is crucial from a stability point of view because, if not maintained, it can pose a great potential hazard for its surroundings. Various modern approaches of chimneys’ geometrical parameters determination have been proposed and are actively in use. However, little research regarding the applicability of the unmanned aerial system (UAS)-based photogrammetric approach of chimney structural monitoring has been conducted and a comprehensive analysis with validated methods is lacking. Therefore, this research is focused on the determination of geometrical structural parameters of a masonry chimney whereby two independent methods have been applied. Reference values of the chimney geometrical parameters have been determined by precise total station (TS) measurements and, in relation to them, the applicability of the UAS-based photogrammetric approach is evaluated. Methodologically, the reference and validation values of the chimney geometrical parameters have been determined based on double modeling of the chimney structure. Firstly, cross-sectional elliptical regression has been applied to determine the geometrical values of the chimney at predefined above-ground levels (AGLs). Secondly, the spatial chimney axis has been derived by polynomial regression to determine the inclination of the full chimney structure. Lastly, the structural stability of the chimney is validated based on its axis inclination whereby permitted deviations are determined according to the European Standard EN 1996-1-1:2005. Experimental results of our research show that consistently better results are gained by TS-based surveys and, although the determination of the chimney’s geometrical values by the UAS-based approach is certainly possible, great attention must be given to the accuracy of the UAS-generated point cloud (PC) if high accuracy results are needed.

For high-precision Global Navigation Satellite Systems (GNSS) positioning based on carrier-phase measurements, knowledge of the GNSS receiver antenna electrical signal reception characteristics, i.e., phase center, is crucial. Numerous studies have led to the understanding of the influence of GNSS receiver antenna phase center corrections (PCCs) on GNSS positioning accuracy and other estimated parameters (e.g., receiver clock estimates, ambiguities, etc.). With the goal of determining the PCC model of GNSS receiver antennas, only a few antenna calibration systems/facilities are in operation or under development worldwide. The International GNSS Service (IGS) publishes type-mean PCC models for almost all geodetic-grade GNSS antennas. However, the type-mean models are not perfect and do not fully reflect the signal reception properties of individual GNSS receiver antennas. Relevant published scientific research has shown that the application of individual PCC models significantly improves the accuracy of GNSS positioning and other estimated parameters. In this article, the new automated GNSS antenna calibration system, recently developed at the Laboratory for Measurements and Measuring Technique (LMMT) of the Faculty of Geodesy of the University of Zagreb in Croatia, is presented. The developed system is an absolute field calibration system based on the utilization of a Mitsubishi MELFA 6-axis industrial robot. During calibration, the robot tilts and rotates the GNSS antenna under test (AUT) around a fixed point within the antenna. The antenna PCC modelling is based on time-differenced double-difference carrier-phase observations. Our preliminary results for the Global Positioning System (GPS) L1 (G01) frequency show a submillimeter repeatability of the estimated PCC model and a submillimeter agreement with the Geo++ GmbH calibration results.

This review provides an extensive overview of the modernization of Global Navigation Satellite System (GNSS), Regional Navigation Satellite System (RNSS), and Satellite-Based Augmentation System (SBAS) up to 28 September 2025. It covers a description of the individual systems, the new launched satellites, and the new civil signals. GNSS includes the United States’ GPS, Russia’s GLONASS, the European Union’s Galileo, and China’s BDS. In the last several years there has been an intensive development of RNSS, which primarily encompass the Japan’s QZSS, India’s IRNSS, and the South Korea’s KPS. The focus of this research is analyzing the possibilities of advancing Position, Navigation, and Timing (PNT) service as well as future perspective and trends in the field of satellite positioning and navigation. SBAS supports satellite systems by providing civil aviation users with corrections and integrity information. Additional to WAAS and EGNOS, this paper examines several more SBAS currently under development. Furthermore, it provides a concise overview and discussion of the above systems, as well as innovations in space technology in the Republic of Croatia. In addition, it emphasizes the influence of political events on the development of satellite systems as well as the role of aerospace companies.

Zbornik radova Građevinskog fakulteta Subotica, Journal of Faculty of Civil Engineering

Precise global navigation satellite system (GNSS) positioning is based on carrier phase observations, where the understanding of the receiver antenna’s phase center corrections (PCCs) is critical. With the main goal of determining the PCC models of GNSS receiver antennas, only a few antenna calibration systems are in operation or under development worldwide. In this paper, a new automated GNSS receiver antenna calibration system, recently developed at the Laboratory for Measurements and Measuring Technique (LMMT) of the Faculty of Geodesy of the University of Zagreb in Croatia, is briefly presented. The developed system is an absolute field calibration system based on the utilization of a Mitsubishi MELFA RV-4FML-Q 6-axis industrial robot. The antenna’s PCC modeling is based on triple-difference carrier phase observations and spherical harmonic (SH) expansion. Our early calibration results for the global positioning system (GPS) L1 frequency show sub-millimeter agreements with the IGS approved Geo++ GmbH values.