Segments-based progressive TIN densification filter for DTM generation from airborne LIDAR data

Airborne light detection and ranging( LIDAR) has revolutionized conventional methods for digital terrain models( DTMs) acquisition. Ground filtering for airborne LIDAR is one of the core steps taken to obtain a high quality DTM. This paper presents a segments-based progressive TIN( triangulated irregular network) densification( SPTD) filter that can automatically separate ground points from non-ground points. The SPTD method is composed of two key steps: point cloud segmentation and clustering by iterative judgement. The clustering method uses the dual distance to obtain a set of seed points as a coarse spatial clustering process. Then the rest of the valid point clouds are classified iteratively. Finally,the datasets provided by ISPRS are utilized to test the filtering performance.In comparison with the commercial software Terra Solid,the experimental results show that the SPTD method in this paper can avoid single threshold restrictions. The expected accuracy of ground point determination is capable of producing reliable DTMs in the discontinuous areas.

Three-dimensional calculation of roadway earthwork volume

To solve the inaccuracy problem caused by the two existing methods (averageend-area method and prismoidal method) used for the calculation of roadway earthwork volume, thispaper puts forward a new concept of the 3-dimensional algorithm that takes all the roadway geometricdesign procedures as a kind of geometrical operation between the ground model (original terrainmodel) and the roadway model (designed model) under certain constraints, and then presents acomplete 3-dimensional algorithm of roadway earthwork volume as well as its executable computerprogram. The algorithm benefits from the re-triangulation technique of constrained delaunaytriangulation (CDT), which can yield a true volume value theoretically. Through a number ofpractical testscovering varied intervals between adjacent cross sections, it is proven to possess ahigher accuracy compared with that of traditional methods. All the work involved in this paperindicates that the 3-dimensional calculation of roadway earthwork volumeis feasible, more accurateand should have further application in practice.

An integrated multiscale approach for characterization of rock masses subjected to tunnel excavation

The design of tunnels must be conducted based on the knowledge of the territory. The longer the structure, the larger the area to be investigated, and the greater the number of surveys and tests to be performed in order to thoroughly examine all the relevant features. Therefore, optimization of the investigation process is strongly required to obtain complete and reliable data for the design of the infrastructure. The fast development of remote sensing technologies and the affordability of their products have contributed to proving their benefits as supports for investigation, encouraging the spreading of automatic or semi-automatic methods for regional scale surveys. Similarly, considering the scale of the rock outcrop, photogrammetric and laser scanner techniques are well-established techniques for representing geometrical features of rock masses, and the benefits of non-contact surveys in terms of safety and time consumption are acknowledged. Unfortunately, in most cases, data obtained at different scales of investigations are only partially integrated or compared, probably due to the missing exchange of knowledge among experts of different fields（e.g. geologists and geotechnical engineers）. The authors,after experiencing such a lack of connection among the results of different surveys concerning tunnels,propose a multiscale approach for the optimization of the investigation process, starting from the regional scale, to obtain the data that can be useful not only for planning more detailed surveys in a preliminary phase, but also for making previsions on the discontinuity sets that are present in the rock masses subjected to excavations. A methodological process is proposed and illustrated by means of a case study. Preliminary results are discussed to highlight the potentiality of this method and its limitations.

Analysis of the factors affecting LiDAR DTM accuracy in a steep shrub area

The creation of a quality Digital Terrain Model(DTM)is essential for representing and analyzing the Earth in a digital form.The continuous improvements in the acquisition and the potential of airborne Light Detection and Ranging(LiDAR)data are increasing the range of applications of this technique to the study of the Earth surface.The aim of this study was to determine the optimal parameters for calculating a DTM by using an iterative algorithm to select minimum elevations from LiDAR data in a steep mountain area with shrub vegetation.The parameters were:input data type,analysis window size,and height thresholds.The effects of slope,point density,and vegetation on DTM accuracy were also analyzed.The results showed that the lowest root mean square error(RMSE)was obtained with an analysis window size of 10 m,5 m,and 2.5 m,rasterized data as input data,and height thresholds equal to or greater than 1.5 m.These parameters showed a RMSE of 0.19 m.When terrain slope varied from 0
10%to 50
60%,the RMSE increased by 0.11 m.The RMSE decreased by 0.06 m when point density was increased from 4 to 8 points/m2,and increased by 0.05 m in dense vegetation areas.

不同机载LiDAR点云滤波算法对比分析

针对目前各种机载点云滤波算法缺乏详细对比的问题,分别从定性和定量两方面对常用的3种滤波算法进行了对比分析,得出了滤波误差最小的滤波方法,以及各滤波算法对不同地形数据的适应情况。利用国际摄影测量与遥感学会(International Society for Photogrammetry and Remote Sensing,ISPRS)提供的标准滤波数据进行实验。结果表明,6组实验数据中,布料模拟滤波算法的总误差都是最小的;对于平坦地形数据,布料模拟滤波算法最合适,对于地形起伏的复杂地形数据,布料模拟滤波算法和渐进三角网滤波算法总误差值接近,但后者的滤波时间更短。