Semi-automated high-accuracy 3D mapping of concrete arch bridges using UAV photogrammetry and intelligently optimized ground control point layouts

Unmanned aerial vehicles, equipped with various sensors and devices, are increasingly used to acquire geospatial data in geodesy, geoinformatics, and environmental studies. In this context, a new research and professional field has been developed – UAV photogrammetry – dealing with photogrammetry data acquisition and data processing, acquired by unmanned aerial vehicles. In this study, we analyse the selected factors that impact the quality of data provided using UAV photogrammetry, with the focus on positional accuracy; they are discussed in three groups: (a) factors related to the camera properties and the quality of images; (b) factors related to the mission planning and execution; and (c) factors related to the indirect georeferencing of images using ground control points. These selected factors are analysed based on the detailed review of relevant scientific publications. Additionally, the influence of the number of ground control points and their spatial distribution on point clouds' positional accuracy has been investigated for the case study. As the conclusion, key findings and recommendations for UAV photogrammetric projects are given; we have highlighted the importance of suitable lighting and weather conditions when performing UAV missions for spatial data acquisition, quality equipment, appropriate parameters of UAV data acquisition, and a sufficient number of ground control points, which should be determined with the appropriate positional accuracy and their correct distribution in the field.

UAV photogrammetry and laser scanning of bridges: a new methodology and its application to a case study

With the advent and development of UAV technologies, UAV images are widely used in various fields since UAV photogrammetry has many advantages in terms of cost and accessibility. In addition, UAV photogrammetry has the advantage of enabling precise 3D surveying because it acquires images of higher spatial resolution with higher overlap compared to traditional aerial photogrammetry. UAV photogrammetry requires ground control points (GCPs) that are dense and evenly distributed throughout the study area. GCP surveying is generally conducted on-site, unlike automated UAV flight and image acquisition, which is a primary factor hindering time and labor cost reduction. In addition, pre-processing, such as UAV orthophoto, point cloud data, and digital elevation model (DEM) production, is performed automatically according to designated parameters, whereas matching GCP survey information with the images involves the intervention of an analyst. Therefore, in this study, the automatic extraction of UAV GCP targets and their centroids was investigated to increase the utilization of UAV photogrammetry and reduce the cost. Sequential steps of image thresholding, boundary detection, and buffered labeling detected a candidate area where ground targets exist. Then, the Hough transform was applied to the target candidates to extract two dominant lines and their intersection point representing the target center. The proposed method extracts the GCP targets from the images with high accuracy, and it was confirmed that it could be applied to complex urban areas. In addition, the GCP targets and their centroid points were successfully extracted from various land covers.

Assessment of UAV-photogrammetric mapping accuracy based on variation of ground control points

This paper reviews international practice in the inspection of bridges, and looks at the NDE of post-tensioned concrete and of masonry arch bridges. Key continental European practice is compared with the UK and the USA. Given the wide range of langua

The most common historic bridge type in California is the concrete bridge. These concrete bridges have a distinct local imprint, the technology is innovative and the designers have placed great emphasis on the aesthetics. The most graceful are the concrete arch bridges, often located in the rugged wilderness of the State.' Many of these historic concrete bridges show sign of deterioration due to corrosion or excessive cracking. They do not meet the current requirement for traffic loading and they no longer have an acceptable safety margin against seismic failure. The present technology for the preservation and seismic strengthening of historic concrete arch bridges in California is demonstrated in case studies. These include the Donner Summit Bridge, a fixed type open spandrel arch bridge in the Sierra Nevada, the Colorado Street Bridge, an eleven span arch bridge in Pasadena, and the Diestelhorst Bridge, a five span concrete arch bridge across the Sacramento River in Northern California.

Structural optimization of concrete arch bridges using Genetic Algorithms

This study examines the impact of the number and placement of Ground Control Points (GCPs) on the accuracy of photogrammetric results using low-cost UAVs. The relevance of this research stems from the growing popularity and applicability of UAV photogrammetry, particularly in areas with diverse terrains and requirements for precise spatial data. The experiment leverages modern photogrammetric techniques, including Structure from Motion (SfM) algorithms, to analyze how GCP configurations affect error distribution and model accuracy. The study's first phase focused on evaluating the influence of GCP placement at varying heights. A photogrammetric survey was conducted at the Kyiv Hippodrome, utilizing terrestrial laser scanning (TLS) to establish high-precision coordinates for control points. The data acquisition involved the DJI Phantom 4 Pro V2 UAV, with multiple flight missions capturing images at 30-degree camera deviations from the nadir. Points were systematically analyzed by alternating their roles as GCPs and Control Points (CPs). The results demonstrated that errors significantly increased when CPs were located further from the UAV camera, emphasizing the need for proximity in GCP placement. The second phase analyzed how GCP configurations and quantities influence photogrammetric model accuracy. By forming 12 groups of GCPs, each varying in distribution and number, the study identified optimal setups for minimizing errors. Groups with evenly distributed points across the survey area, comprising at least eight GCPs, exhibited the lowest root mean square errors (RMSE). Conversely, configurations with GCPs concentrated along a single side or solely on the survey area's edges resulted in substantial inaccuracies. Key findings reveal that an effective GCP placement strategy involves prioritizing proximity to the UAV camera and achieving even distribution across the surveyed area. Additionally, configurations with fewer than eight GCPs tend to suffer from sharp declines in accuracy. The research underscores the importance of balancing GCP quantity and placement for achieving reliable photogrammetric outputs in low-cost UAV applications

Recently, China has made good progress in the construction of concrete arch bridges, which can provide development and experience for bridge engineers worldwide. Data from 313 concrete arch bridges with span lengths of no less than 100 m are studied. The investigation and analysis results indicate that both the number and the span lengths of these concrete arch bridges increased after 2007. Railway bridge applications have been increasing rapidly, while lightweight concrete arch bridges were not built anymore. The material strength of main arches has continuously improved. Ultra-high performance concrete (UHPC) is a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement. Some UHPC arch bridges with small span lengths have been built. The cantilever method continues to be the main erection method used. The innovation-involving introduction of the Concrete-Filled Steel Tube (CFST) trussed arch into the Melan method enables construction economically, and it significantly reduces the required steps in casting of the main concrete arch. This approach has been used for all arch bridges with span lengths greater than 250 m after 2007. The core concrete is generally of higher strength grade than that of the concrete encasing the CFST. Finally, two concrete arch bridges are introduced as case studies, one has the current span record and the other would have the new span record when completed.

The rapid, up-to-date, cost-effective acquisition and tracking of intertidal topography are the fundamental basis for timely, high-priority protection and restoration of the intertidal zone. The low cost, ease of use, and flexible UAV-based photogrammetry have revolutionized the monitoring of intertidal zones. However, the capability of the RTK-assisted UAV photogrammetry without ground control points, the impact of flight configuration difference, the presence of surface water in low-lying intertidal areas on the photogrammetric accuracy, and the potential of UAV/satellite Synergy remain unknown. In this paper, we used an RTK-assisted UAV to assess the impact of the above-mentioned considerations quantitatively on photogrammetric results in the context of annual monitoring of the Chongming Dongtan Nature Reserve, China based on an optimal flight combination. The results suggested that (1) RTK-assisted UAVs can obtain high-accuracy topographic data with a vertical RMSE of 3.1 cm, without the need for ground control points. (2) The effect of flight altitude on topographic accuracy was most significant and also nonlinear. (3) The elevation obtained by UAV photogrammetry was overestimated by approximately 2.4 cm in the low-lying water-bearing regions. (4) The integration of UAV and satellite observations can increase the accuracy of satellite-based waterline methods by 51%. These quantitative results not only provide scientific insights and guidelines for the balance between accuracy and efficiency in utilizing UAV-based intertidal monitoring, but also demonstrate the great potential of combined UAV and satellite observations in identifying coastal erosion hotspots. This establishes high-priority protection mechanisms and promotes coastal restoration.

Abstract. Nowadays UAVs have been widely used for large scale surveying and mapping. Compared with traditional surveying techniques, UAV photogrammetry is more convenient, cost-effective, and responsive. Aerial images, Position and Orientation System (POS) observations and coordinates of ground control points are usually acquired during a surveying campaign. Aerial images are the data source of feature point extraction, dense matching and ortho-rectification procedures. The quality of the images is one of the most important factors that influence the accuracy and efficiency of UAV photogrammetry. Image processing techniques including image enhancement, image downsampling and image compression are usually used to improve the image quality as well as the efficiency and effectiveness of the photogrammetric data processing. However, all of these image processing techniques bring in uncertainties to the UAV photogrammetry. In this work, the influences of the aforementioned image processing techniques on the accuracy of the automatic UAV photogrammetry are investigated. The automatic photogrammetric data processing mainly consists of image matching, relative orientation, absolute orientation, dense matching, DSM interpolation and orthomosaicing. The results of the experiments show that the influences of the image processing techniques on the accuracy of automatic UAV photogrammetry are insignificant. The image orientation and surface reconstruction accuracies of the original and the enhanced images are comparable. The feature points extraction and image matching procedures are greatly influenced by image downsampling. The accuracies of the image orientations are not influenced by image downsampling and image compression at all.

The two-dimensional finite element method can be used to calculate the thermal field distribution of prestressed concrete bridge girders. However, this method is not appropriate for the concrete box-girder arch bridges, because they have different azimuth and dip angles at the top and bottom flanges along arch axis. Thus, an experimental and analytical study was conducted on a concrete box-girder arch bridge located in Guizhou, China, to investigate the thermal behavior under convection and the solar radiations. To determine the vertical temperature gradients, a two-dimensional plane finite element model was used to calculate the thermal field based on meteorological parameter methods. In addition, the three-dimensional beam finite element model was proposed to study the thermal stress and displacement of arch bridges using the vertical temperature gradients. Finally, the thermal behavior of the concrete box-girder arch bridges determined by the two-dimensional plane and three-dimensional beam finite element model was verified by three-dimensional solid finite element model.

Concrete-Filled Steel Tube Arch Bridges in China

The arch bridge is one of the main bridge types utilized in China, and many concrete arch bridges have been built there. Concrete with its high strength in compression and limited strength in tension is an ideal construction material for the arch since its primary internal force is compression. This paper briefly introduces the construction of concrete arch bridges in China in recent years, provides basic statistics on concrete arch bridges worldwide with a span of more than 200 m, analyses the development of concrete arch bridges, and focuses on the Nanpanjiang and Beipanjian Railway Bridges. Furthermore, this study introduces the common construction methods for concrete arch bridges, and describes the recent progress of research on concrete arch bridges using new materials and structures. Finally, future trends in the research and development of concrete arch bridges are discussed including applications of new materials, structures and construction methods.

Concrete arch bridge with steel webs is a modification of the conventional reinforced concrete arch bridge by replacing the concrete webs with the corrugated or plain steel webs. In this study, a finite element model of the reinforced concrete arch bridge and the concrete arch bridge with corrugated or plain steel webs were developed using a nonlinear finite element program, NL_Beam3D. Their nonlinear seismic responses were studied and compared. The results demonstrate that axial force and out-of-plane bending moment are predominant under out-of-plane seismic excitations, and the materials at the arch springing have reached the plastic stage. On the other hand, axial force and in-plane bending moment are predominant under longitudinal seismic excitations, and the materials still remain in the elastic state. It is also found that seismic responses under out-of-plane excitations are greater than that under longitudinal excitations. For concrete arch bridges with steel webs, it is unnecessary to consider the effects of synchronous out-of-plane and longitudinal seismic excitations. RC-PSW arch bridge has better seismic performance than RC-PSW arch bridge.