机载LiDAR点云数据精度评定方法的研究

基于机载LiDAR系统组成及工作原理,对激光点云数据精度评定方法进行研究,主要包括内插特征点对比分析法、统计分析法、斜面几何分析法、误差传播定律分析法。各种方法都有各自的优缺点,在进行具体精度评定时,几种方法要结合使用。     

Updating digital elevation models via change detection and fusion of human and remote sensor data in urban environments

OpenStreetMap (OSM) currently represents the most popular project of Volunteered Geographic Information (VGI): geodata are collected by common people and made available for public use. Airborne Laser Scanning (ALS) enables the acquisition of high-resolution digital elevation models that are used for many applications. This study combines the advantages of both ALS and OSM, offering a promising new approach that enhances data quality and allows change detection: the mainly up-to-date 2D data of OSM can be combined with the high-resolution – but rarely updated – elevation information provided by ALS. This case study investigates building objects of OSM and ALS data of the city of Bregenz, Austria. Data quality of OSM is discerned by the comparison of building footprints using different true positive definitions (e.g. overlapping area). High quality of OSM data is revealed, yet also limitations of each method with respect to heterogeneous regions and building outlines are identified. For the first time, an up-to-date Digital Surface Model (DSM) combining 2D OSM and ALS data is achieved. A multitude of applications such as flood simulations and solar potential assessments can directly benefit from this data combination, since their value and reliability strongly depend on an up-to-date DSM.     

3-D voxel-based solid modeling of a broad-leaved tree for accurate volume estimation using portable scanning lidar

We developed a method to produce a 3-D voxel-based solid model of a tree based on portable scanning lidar data for accurate estimation of the volume of the woody material. First, we obtained lidar measurements with a high laser pulse density from several measurement positions around the target, a Japanese zelkova tree. Next, we converted lidar-derived point-cloud data for the target into voxels. The voxel size was 0.5 cm × 0.5 cm × 0.5 cm. Then, we used differences in the spatial distribution of voxels to separate the stem and large branches (diameter > 1 cm) from small branches (diameter ⩽ 1 cm). We classified the voxels into sets corresponding to the stem and to each large branch and then interpolated voxels to fill out their surfaces and their interiors. We then merged the stem and large branches with the small branches. The resultant solid model of the entire tree was composed of consecutive voxels that filled the outer surface and the interior of the stem and large branches, and a cloud of voxels equivalent to small branches that were discretely scattered in mainly the upper part of the target. Using this model, we estimated the woody material volume by counting the number of voxels in each part and multiplying the number of voxels by the unit voxel volume (0.13 cm³). The percentage error of the volume of the stem and part of a large branch was 0.5%. The estimation error of a certain part of the small branches was 34.0%.     

机载激光雷达数据滤波和人工编辑

高精度的DTM/DEM是获取基础地理信息数据进行建筑物重建、道路提取、植被分析的重要数据源。机载LiDAR系统的主要任务之一就是解决如何得到高质量的DTM的问题。文中针对机载LiDAR数据滤波和滤波后人工编辑展开研究。由于任何一种滤波算法,都有一定的局限性,从实际应用的角度来说,人工编辑仍然起着重要的作用,因此,研究重点围绕滤波后的人工编辑展开,旨在探求工程应用中高效、快速、准确的DTM获取途径,为工程实践提供技术支持。     

机载LiDAR数据逐航带平差与航带区域网平差对比

机载LiDAR系统获取的点云数据在经过预处理解算后仍会残余部分系统误差,因此,在利用点云数据生成DEM等相关数字产品之前,必须检查并改正这部分系统误差。以此为主要目标,本文对机载LiDAR数据的逐航带平差与航带区域网平差展开研究,并以Microsoft Visual Studio 2008 C++为开发平台、基于实测数据对比了两者在完成多航带构成的测区平差时的精度,结果表明:机载LiDAR数据的航带区域网平差方法相较于LZD算法可有效降低逐航带平差导致的误差累积,精度更高。     

机载LiDAR数据的多回波信息分析及应用研究

本文通过分析机载LiDAR系统获取的激光数据的多回波特性,阐述了多回波信息对地物类型信息的揭示作用,并将多回波特性用于减少参与滤波的激光脚点数量。实验证明,本文提出的滤波方案,可以预先剔除掉大部分的植被激光脚点和部分的建筑物激光脚点,既减少了参与滤波的数据量,又可以改善滤波算法对建筑物和植被的滤除效果。     

复杂地区机载SAR数据获取航线规划

本文主要论述机载SAR数据获取航线规划,提出了适合于地形复杂地区机载SAR航摄的航线规划方案。详细说明了航线设计方法,并引入低分辨率的DEM数据,对航线规划结果进行了模拟;最后对机载合成孔径雷达航摄进行三维模拟,以期更好地显示并检验航线规划结果。     

航空地球物理勘探资料微调平处理

航空物探测量中测线间水平往往存在差异,表现为沿测线方向的条带。调平处理旨在减少或消除测线间的水平差,是航空物探资料处理中的关键,对航空物探资料处理和解释具有重要作用。笔者以实际的航磁资料处理为例,详细介绍了航空物探资料微调平处理的原理与实现。微调平处理中首先通过方向滤波从原始资料中提取噪声网格,并按飞行测线提取噪声网格中的数据并分离有用的地质信息,最终将分离后的测线水平误差从原始资料中去除得到调平后资料,以此实现航空物探资料的微调平处理。同时,针对资料处理中遇到的诸如滤波器选取、异常分离阈值确定、最终调平效果检验等实际问题进行讨论,这对理解微调平并应用于实际资料处理均具有意义。     

向下延拓航空重力数据的Tikhonov双参数正则化法

为了避免正则化参数对向下延拓过程可靠成分的修正影响,提出了Tikhonov双参数正则化法。引进截断参数,将法矩阵的奇异值分为相对较大的奇异值（可靠部分）和相对较小的奇异值（不可靠部分）;引进正则化参数,只对法矩阵的小奇异值进行修正,以抑制高频误差对向下延拓解的影响。采用改进的广义交互确认法（GCV）确定截断参数和正则化参数。基于EGM2008重力场模型仿真了一组航空重力数据,验证了该方法对航空重力数据向下延拓过程的有效性。     

顾及地形特征的机载LiDAR数据桥梁提取算法研究

提出了一种从机载LiDAR点云数据中提取水陆桥梁的新算法,采用先滤波分类再识别桥梁的策略用于桥梁主体及其与地面连接处脚点的提取。首先对机载LiDAR点云数据进行严格滤波,在此基础上利用多个阈值对非地面脚点进行初步提取;然后引入Alpha-shapes算法对初步提取结果进行分割,并辅以面积阈值提取出属于桥梁主体部分的脚点;最后提出一种顾及地形特征的点云区域生长算法,用于准确提取桥梁主体与地面连接部分的脚点。实验证明,本文算法对水面和陆地桥梁提取均有很好的效果。