Photogrammetry-based free jet trajectory 3D reconstruction technology

The subject of this study, which is the focus of this article, is the three-dimensional reconstruction of the trajectory of a free jet of fire-extinguishing agent based on full-scale tests of firefighting monitor systems. The resulting geometric shapes are used in the synthesis and debugging of computer vision systems, control algorithms for firefighting robots, and the construction and validation of mathematical and neural network models of the studied flow processes. Key features of free jets in this applied field include their large scale, dynamically changing boundary shapes, variable optical density across different regions, and more, which significantly complicates the application of existing 3D reconstruction methods. The aim of this work is to develop a technology for modeling the trajectories of fire-extinguishing agents that can address these challenges. This study proposes a methodology for conducting full-scale tests of monitor systems on a pre-marked experimental site with synchronized video recording of the free jet in three planes, including the use of an onboard camera from an unmanned aerial vehicle. Additionally, an algorithm for 3D trajectory reconstruction based on the obtained digital images was developed, taking into account the geometric features of the studied flow processes. The article presents the results of testing the developed technology in studying the motion of a fire-extinguishing agent stream from a fire monitor nozzle under the influence of crosswinds which can significantly deflect the jet laterally. A 3D model of the investigated trajectory was constructed using digital images captured during the experiment. A comparative analysis of the jet geometric characteristics (height, range, and lateral deflection) — calculated from the reconstruction results and measured during full-scale tests — showed a maximum relative error of 3.7 %, indicating the high accuracy of the proposed method. The practical significance of this technology lies in its ability to obtain high-spatial-resolution empirical data in free-jet studies. These data can be used to validate models describing jet motion based on computational fluid dynamics and machine learning methods, particularly in the development of computer vision systems and fire-extinguishing agent targeting algorithms that account for external disturbances in robotic firefighting systems.

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