Dubravko Gajski

Dr. Dubravko Gajski

Department of Photogrammetry & Remote Sensing, University of Zagreb, Faculty of Geodesy, Zagreb, Zagreb, Grad, Croatia

Research Focus & Metrics

Academic Career Length

11Years (2016-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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9 October 2018 in Survey Review
Verified
Journal Article
Closed access
Admir MulahusicAdmir Mulahusic
Admir Mulahusic
NTNedim Tuno
Nedim Tuno
DGDubravko Gajski
Dubravko Gajski
JTJusuf Topoljak
Jusuf Topoljak
Laser scanning does not provide unlimited geometrical accuracy and integrity when scanning complex objects. Scanning systems have a minimum and maximum range in which they operate, depending on the technical characteristics. Scanning below or above these limits results in gross errors and registering of incorrect data. Laser scanners can have difficulties with certain materials such as marble and reflective surfaces. This paper presents the results of laser scanning of a complex monument of cultural and historical heritage using two different types of terrestrial laser scanners. Afterwards, the comparison and analysis of the results are shown. The scanners used were terrestrial laser scanners Faro Focus 3D (phase mode distance measurements) and STONEX X300 (pulse mode distance measurements).

6 June 2016 in The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Verified
Journal Article
Open access
Mateo GašparovićMateo Gašparović
Mateo Gašparović
DGDubravko Gajski
Dubravko Gajski
The development of unmanned aerial vehicles (UAVs) and continuous price reduction of unmanned systems attracted us to this research. Professional measuring systems are dozens of times more expensive and often heavier than "amateur", non-metric UAVs. For this reason, we tested the DJI Phantom 2 Vision Plus UAV. Phantom’s smaller mass and velocity can develop less kinetic energy in relation to the professional measurement platforms, which makes it potentially less dangerous for use in populated areas. In this research, we wanted to investigate the ability of such non-metric UAV and find the procedures under which this kind of UAV may be used for the photogrammetric survey. It is important to emphasize that UAV is equipped with an ultra wide-angle camera with 14MP sensor. Calibration of such cameras is a complex process. In the research, a new two-step process is presented and developed, and the results are compared with standard one-step camera calibration procedure. Two-step process involves initially removed distortion on all images, and then uses these images in the phototriangulation with self-calibration. The paper presents statistical indicators which proved that the proposed two-step process is better and more accurate procedure for calibrating those types of cameras than standard one-step calibration. Also, we suggest two-step calibration process as the standard for ultra-wideangle cameras for unmanned aircraft.

6 June 2016 in The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Verified
Journal Article
Open access
PDF file
Mateo GašparovićMateo Gašparović
Mateo Gašparović
DGDubravko Gajski
Dubravko Gajski
The development of unmanned aerial vehicles (UAVs) and continuous price reduction of unmanned systems attracted us to this research. Professional measuring systems are dozens of times more expensive and often heavier than "amateur", non-metric UAVs. For this reason, we tested the DJI Phantom 2 Vision Plus UAV. Phantom’s smaller mass and velocity can develop less kinetic energy in relation to the professional measurement platforms, which makes it potentially less dangerous for use in populated areas. In this research, we wanted to investigate the ability of such non-metric UAV and find the procedures under which this kind of UAV may be used for the photogrammetric survey. It is important to emphasize that UAV is equipped with an ultra wide-angle camera with 14MP sensor. Calibration of such cameras is a complex process. In the research, a new two-step process is presented and developed, and the results are compared with standard one-step camera calibration procedure. Two-step process involves initially removed distortion on all images, and then uses these images in the phototriangulation with self-calibration. The paper presents statistical indicators which proved that the proposed two-step process is better and more accurate procedure for calibrating those types of cameras than standard one-step calibration. Also, we suggest two-step calibration process as the standard for ultra-wideangle cameras for unmanned aircraft.

15 June 2016 in The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Verified
Journal Article
Open access
DGDubravko Gajski
Dubravko Gajski
ASA. Solter
A. Solter
Mateo GašparovićMateo Gašparović
Mateo Gašparović
Many valuable archaeological artefacts have the size of a few centimetres or less. The production of relevant documentation of such artefacts is mainly limited to subjective interpretation and manual drawing techniques using a magnifier. Most of the laser scanners available for the archaeological purposes cannot reach sufficient space resolution to gather all relevant features of the artefact, such as the shape, the relief, the texture and any damage present. Digital photogrammetric techniques make measuring with high accuracy possible and such techniques can be used to produce the relevant archaeometric documentation with a high level of detail. The approaches for shooting a good macro photograph (in the photogrammetric sense) will be explored and discussed as well as the design of a calibration test-field and the self-calibration methods suitable for macro photogrammetry. Finally, the method will be tested by producing a photorealistic 3D-model of an ancient figurine.

1 January 2018 in CATENA
Verified
Journal Article
Closed access
VGVlatko Gulam
Vlatko Gulam
DGDubravko Gajski
Dubravko Gajski
LPLászló Podolszki
László Podolszki

24 July 2025 in Remote Sensing
Verified
Journal Article
Open access
PDF file
AMAnte Marendić
Ante Marendić
DGDubravko Gajski
Dubravko Gajski
Ivan DuvnjakIvan Duvnjak
Ivan Duvnjak
Rinaldo Ivan PaarRinaldo Ivan Paar
Rinaldo Ivan Paar
The safety and longevity of engineering structures depend on precise and timely monitoring, especially during load testing inspections. Conventional displacement measurement methods—such as LVDT sensors, GNSS, RTS, and levels—each present benefits and limitations in terms of accuracy, applicability, and practicality. Photogrammetry has emerged as a promising alternative, offering non-contact measurement, cost-effectiveness, and adaptability in challenging environments. This study investigates the potential of photogrammetric methods for determining structural displacements during load testing in real-world conditions where such approaches remain underutilized. Two photogrammetric techniques were tested: (1) a single-image homography-based approach, and (2) a multi-image bundle block adjustment (BBA) approach using both UAV and tripod-mounted imaging platforms. Displacement results from both methods were compared against reference measurements obtained by traditional LVDT sensors and robotic total station. The study evaluates the influence of different camera systems, image acquisition techniques, and processing methods on the overall measurement accuracy. The findings suggest that the photogrammetric method, especially when optimized, can provide reliable displacement data with sub-millimeter accuracy, highlighting their potential as a viable alternative or complement to established geodetic and sensor-based approaches in structural testing.