DATA PROCESSING TECHNOLOGY OF AIRBORNE 3D IMAGE

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基于DSM点云纠正的正射影像房屋边缘锯齿消除

当前无人机低空航空摄影测量生成的数字正射影像DOM中,房屋边缘大量存在锯齿失真的现象,严重影响了对影像建筑物的判读和提取,降低了无人机航测数字正射影像的使用效益。提出一种利用数字表面模型DSM点云数据,提取其房屋边缘,并进行规则化处理,然后在此基础上进行数字微分纠正,生成正射影像的方法。实验结果表明,利用该方法可有效防止数字正射影像中房屋边缘存在的锯齿失真现象。     

不同格网密度的DSM/DEM对影像分类精度的影响研究

在无控制点的卫星影像正射校正中,大多采用DSM/DEM数据作为辅助数据来消除或限制因地形起伏引起的形变,然而经不同格网密度的DSM/DEM正射校正后的影像对后续处理会产生不同程度的影响,如对地物分类精度产生影响。针对这一问题,本文分别采用不同的DSM/DEM数据(China DSM 15 m、ASTER GDEM 30 m和SRTM 90 m)对资源三号影像进行正射校正,然后对正射校正后影像利用支持向量机进行分类,比较正射校正后影像结果的分类精度。结果表明:在相同重采样方法下,影像经China DSM 15 m DSM正射校正后结果的分类精度优于ASTER GDEM 30 m DEM和SRTM 90 m DEM。     

平坦地区DSM到DEM的试验

讨论了平坦地区根据影像匹配的结果将DSM修正成DEM的方法,针对平坦地区一般都有建筑物和树木,利用其本身的地形特点,提出附近最小值方法自动修正DSM以获得近似正确DEM的方法。并对试验结果的精度进行了检查,发现试验的结果比影像匹配后的结果要精确许多,将建筑物和树木等植被的高程去掉,得到比较精确的DEM数据。     

从DSM数据中自动提取建筑物的方法研究

现今,DSM的获取日趋方便、快捷、精确,充分利用DSM所提供的信息,可以解决很多实际问题.本文提出了一种从DSM自动提取建筑物的方法,首先从DSM中提取DTM,差值后得到消除了地形影响的规格化的DSM(即NDSM),然后对NDSM进行改进型"标记控制的分水岭"分割,得到地上物目标;最后根据这些目标的各自特点进行过滤,祛除非建筑物对象,留下我们所要的建筑物对象.     

基于机载LIDAR技术快速建立3维城市模型研究

传统的3维数据获取方法已不能满足城市日益加快的发展速度,机载LIDAR技术作为一种方便、快捷、高效的3维数据获取方法,正在逐步得到广泛认同.目前,机载LIDAR硬件和系统集成发展已比较完善,研究重点主要集中在数据后处理及应用等方面.本文结合国际上最新研究进展,系统介绍了机载LIDAR数据的后处理过程,提出了一种实用的3维城市模型,实现了基于LIDAR数据3维城市模型的快速重建,使该技术能更好地服务于城市信息化建设.     

海量DSM数据的网络轻量化可视化方法

网络环境下海量DSM数据的轻量化可视化是当前网络三维GIS研究的前沿问题之一。针对已有的海量三维模型数据网络可视化效率低、交互性差等问题,提出一种海量DSM数据的网络轻量化可视化方法。针对WebGL技术的特点,通过优化海量DSM数据的组织管理、LODs自适应选择与动态调度等关键技术,设计实现了海量DSM数据网络轻量化可视化算法,研发了原型系统,并以城市倾斜摄影测量DSM数据为例进行了典型实验与分析。实验结果表明,网络可视化实时帧率稳定在40 FPS左右,证明了该方法的有效性与可行性。     

Creating high-resolution bare-earth digital elevation models (DEMs) from stereo imagery in an area of densely vegetated deciduous forest using combinations of procedures designed for lidar point cloud filtering

For areas of the world that do not have access to lidar, fine-scale digital elevation models (DEMs) can be photogrammetrically created using globally available high-spatial resolution stereo satellite imagery. The resultant DEM is best termed a digital surface model (DSM) because it includes heights of surface features. In densely vegetated conditions, this inclusion can limit its usefulness in applications requiring a bare-earth DEM. This study explores the use of techniques designed for filtering lidar point clouds to mitigate the elevation artifacts caused by above ground features, within the context of a case study of Prince William Forest Park, Virginia, USA. The influences of land cover and leaf-on vs. leaf-off conditions are investigated, and the accuracy of the raw photogrammetric DSM extracted from leaf-on imagery was between that of a lidar bare-earth DEM and the Shuttle Radar Topography Mission DEM. Although the filtered leaf-on photogrammetric DEM retains some artifacts of the vegetation canopy and may not be useful for some applications, filtering procedures significantly improved the accuracy of the modeled terrain. The accuracy of the DSM extracted in leaf-off conditions was comparable in most areas to the lidar bare-earth DEM and filtering procedures resulted in accuracy comparable of that to the lidar DEM.     

Recording inter-annual changes on a boulder beach in Galicia,NW Spain using an unmanned aerial vehicle

An unmanned aerial vehicle (UAV) was flown over a boulder beach (area 20 000 m²) on the southern coast of Galicia (northwestern Spain) in May 2016, continuing earlier work based on flights over the same beach in July 2012, May 2013, and late March 2014. Digital surface models (DSMs) with 1.8 cm resolution were constructed from the 2014 and 2016 data to identify changes in beach morphology over the intervening period. Analyses were conducted using a Limit of Detection (LoD) of 0 cm and 3.71 cm. In both cases, the analyses showed that erosion dominated over 19% of the beach area. Accretion occurred over the rest of the beach, which acquired an additional 1500 m³ of material over the study period. Re-analysis of the data from earlier flights suggested that erosion dominated on the beach in 2012–2013 and deposition in 2013–2014. Without any clear relationship between beach behaviour and storm severity during each winter period, it is proposed that gravitationally induced erosion and storm-wave induced deposition are the result of perturbations about an equilibrium beach gradient. The UAV data also suggested that an essentially random component modulates regional patterns of movement. © 2018 John Wiley & Sons, Ltd.     

基于小波多分辨率方向高程限差的LiDAR数据滤波

本文在研究了小波多分辨率分析原理的基础上,将小波变换引入到机载LIDAR数据滤波中,利用金字塔分层理论实现原始DSM数据的快速组织,加快计算速度,提高滤波效率。同时在滤波阈值选择中顾及整个区域的方向高程差,使判断条件更加符合地形特点,提高滤波的准确度。本文最后利用实际的LIDAR数据进行了实验和精度分析。