Attitude Mounting Misalignment Estimation Method for the Calibration of UAV LiDAR System by using a TIN-based Corresponding Model

In traditional attitude mounting misalignment estimation methods for the calibration of unmanned autonomous vehicle (UAV) based light detection and ranging (LiDAR) system, signalized targets and iterative corresponding models are required, which makes it highly cost and computationally time-consuming. This paper presents an attitude mounting misalignment estimation (AMME) method for the calibration of UAV LiDAR system. The proposed method is divided into the coarse registration of LiDAR strips and the estimation of the attitude mounting misalignment. Firstly, 3D keypoints are extracted in the point clouds using the scale-invariant feature transform (SIFT) algorithm. Afterwards, the point feature transform (PFH) descriptor is used for 3D keypoint matching. Then, the coarse registration is executed. In the second part of the contribution, the systematic errors in the attitude mounting misalignment are estimated by incorporating the proposed triangular irregular network (TIN) corresponding model into the calibration modelling. Using the TIN-based corresponding model saves time and cost for AMME method. Furthermore, it provides two important effects: practical and computational, as no designed calibration boards, segmentation and iterative matching are needed. The performance of the proposed method is demonstrated under an UAV LiDAR data onboarded with lightweight navigation sensors. The experimental results show the efficacy of the method in comparison with a state-of-the-art method.

Procjena prostorne raspodjele oborina u GIS okruženju

Oborine su izrazito varijabilna komponenta bilance voda, koja ovisi o nizu faktora, kao što su geografski položaj, udaljenost od mora i nadmorska visina, a ključne su u razumijevanju hidroloških procesa nekog područja. Mjerenja oborina provode se na diskretnim lokacijama meteoroloških postaja (osim u slučaju radarskih opažanja oborina) te su saznanja o njihovoj varijabilnosti u prostoru rezultat primjene različitih metoda interpolacije izmjerenih vrijednosti u točki na analiziranom prostoru. U GIS okruženju, oborina može biti prikazana u formi diskretnog ili kontinuiranog polja pa će o tome ovisiti i odabir metode interpolacije. U radu su, na primjeru srednjih godišnjih količina oborina za razdoblje 1961. – 1990. na području Istre, prikazane i uspoređene tri najčešće primjenjivane metode prostorne interpolacije: Thiessenovi poligoni, TIN (Triangular Irregular Network) te VLR (metoda višestruke linearne regresije). Prve dvije metode ne uzimaju u obzir faktore koji utječu na količinu palih oborina, već su procijenjene vrijednosti u funkciji udaljenosti promatrane točke od oborinskih postaja. Za razliku od njih, metoda višestruke linearne regresije omogućuje određivanje vrijednosti oborina u prostoru u ovisnosti o drugim čimbenicima; u ovome slučaju to su geografski položaj, udaljenost od mora te nadmorska visina.

PS Selection Method for and Application to GB-SAR Monitoring of Dam Deformation

Ground-based synthetic aperture radar (GB-SAR) is a relatively new technique that can be used to monitor the deformation of large-volume targets, such as dams, slopes, and bridges. In this study, the permanent scatterer (PS) technique is used to address the issues encountered in the continuous monitoring of the external deformation of an arch-gravity dam in a hydraulic and hydropower engineering structure in Hubei, China; the technique includes large image data sizes, high accuracy requirements, a susceptibility of the monitoring data to atmospheric disturbances, complex phase unwrapping, and pronounced decoherence. Through an in-depth investigation of PS extraction methods, a combined PS selection (CPSS) method is proposed by fully taking advantage of the signal amplitude and phase information in the monitored scene. The principle and implementation of CPSS are primarily studied. In addition, preliminarily selected PS candidates are directly used to construct and update a triangular irregular network (TIN) to maintain the stability of the subsequent Delaunay TIN. To implement this method, a differential-phase standard-deviation threshold method is proposed to extract PSs that are highly spatially coherent and consistent. Finally, the proposed CPSS was applied to the safety monitoring of the dam. The monitoring results are compared with conventional inverted plumb line monitoring results, and the proposed CPSS is found to be effective and reliable.

Inverse Distance Weight Spatial Interpolation for Topographic Surface 3D Modelling

Topographic modelling is an important aspect in engineering work and planning such as dam design, road planning, volumetric calculation, water flow analysis and so forth. To get topographic data, usually a land survey or topographic measurement is taking for a region or an area under study. A number of points that represent an area are measured to get a height dataset. The dataset which is consist of height points will be used to model topographic condition of the area with generating contour map and also 3D model. There are some methods can be used to generate topographic surface in 3D model like linear interpolation in Triangular Irregular Network (TIN), Kriging and Inverse Distance Weight (IDW). This research implemented IDW spatial interpolation algorithm to model earth surface or topographic model in 3D. The IDW method was implemented in Python programming language using Numpy library for computation and Plotly graphic library to visualize the 3D Model. Using 2500 and 10000 interpolation points with 100 random sampling points that extracted from Digital Surface Model (DSM), IDW was successfully estimated the height at unsampled locations. The results show, more higher interpolation point number will produce more detail surface texture. Keywords : IDW, Topographic, 3D Modelling

Use of Drones for the Topo-Bathymetric Monitoring of the Reservoirs of the Segura River Basin

The Segura River Basin (SRB), located in the South East of Spain, has the lowest percentage of renewable water resources of all the Spanish basins. Therefore, knowledge of the annual rate of water reservoir sedimentation is an important issue to be resolved in one of the most water-stressed regions in the western Mediterranean basin. This paper describes the sensors developed in collaboration with technology-based enterprises (aerial drone, floating drone, and underwater drone), and the methodology for integration of the different types of data acquired to monitor the reservoirs of the SRB. The proposed solution was applied to 21 reservoirs of the SRB. The proposed methodology is based on the use of unmanned aerial vehicles (UAV) for photogrammetry of the reservoir surface area. For each reservoir, two flights were completed, with 20 cm and 5 cm resolution, respectively. Then, a triangular irregular network mesh was generated by GIS techniques. Surface water vehicles (USV) and underwater remote-operated vehicles (ROV) were used to undertake bathymetric surveys. In addition, water quality measurements were made with an ROV device. The main results consist of topographic and bathymetric measurements for each reservoir, obtained by using equipment based on OpenSource technology. According to the results, the annual rate of storage capacity loss of water resources in the SRB´s reservoirs is 0.33%.

An Improved Progressive TIN Densification Filtering Method Considering the Density and Standard Variance of Point Clouds

The progressive TIN (triangular irregular network) densification (PTD) filter algorithm is widely used for filtering point clouds. In the PTD algorithm, the iterative densification parameters become smaller over the entire process of filtering. This leads to the performance—especially the type I errors of the PTD algorithm—being poor for point clouds with high density and standard variance. Hence, an improved PTD filtering algorithm for point clouds with high density and variance is proposed in this paper. This improved PTD method divides the iterative densification process into two stages. In the first stage, the iterative densification process of the PTD algorithm is used, and the two densification parameters become smaller. When the density of points belonging to the TIN is higher than a certain value (in this paper, we define this density as the standard variance intervention density), the iterative densification process moves into the second stage. In the second stage, a new iterative densification strategy based on multi-scales is proposed, and the angle threshold becomes larger. The experimental results show that the improved PTD algorithm can effectively reduce the type I errors and total errors of the DIM point clouds by 7.53% and 4.09%, respectively, compared with the PTD algorithm. Although the type II errors increase slightly in our improved method, the wrongly added objective points have little effect on the accuracy of the generated DSM. In short, our improved PTD method perfects the classical PTD method and offers a better solution for filtering point clouds with high density and standard variance.

VIRTUAL GRAPHIC REPRESENTATION OF CONSTRUCTION EQUIPMENT FOR DEVELOPING A 3D EARTHWORK BIM

BIM provides a visualization of the construction design that allows a construction manager to review the construction process and the information that is associated with the progress. BIM is usually applied to modeling struc­tural objects with parametric geometry where the sequence of process can be predefined. However, BIM technology can also be applied to objects with irregular shape where parametric modeling is not possible such as earthwork topography based on TIN (Triangular Irregular Network).The objective of this research is to develop a 3D earthwork BIM method­ology and provide a graphic simulation that is capable of assisting construction equipment operators during excavation work. The 3D earthwork BIM presents a modeling technique that involves integrating hardware and software technolo­gies. This combination of technologies is used to represent the actual excavator configuration in a 3D virtual environ­ment. When it is applied to actual excavation work, it was proved that the 3D earthwork BIM could synchronize the virtual excavator configuration with the actual excavator configuration during excavation work in real time.