三维几何体的验证规则及修复方法研究

为满足三维应用的需要,人们开始关注真三维几何体的创建来支撑现实世界中的各种三维对象,这些三维对象可能是一般三维体,也可能是非流形的三维几何体。给出了一种满足现实世界对象要求的三维几何体定义,详细分析了这种三维几何体所需要满足的各种规则,进而结合实例给出了相应的验证方法,同时就三维建模时三维几何体数据的修复问题进行了讨论。     

无人机倾斜摄影测量在规划竣工测量中的辅助应用

宁波市建设项目竣工测量成果(高精度实景三维模型)统一提交于建设项目竣工测验合一审批服务平台,以更加便捷、高效、直观和智能地实现“竣工测验合一”工作。针对传统竣工测量难以完成三维建模的现状,本文在竣工施测后运用无人机倾斜摄影技术对天御府小区进行了三维建模。实验表明,无人机获取的三维模型精度较高,不存在扭曲悬挂和碎片漏洞,也不存在纹理缺失。通过与全站仪测量数据对比,发现基于三维模型的平面精度、高程精度和地物点间距精度也能满足“竣工测验合一”的精度要求。     

真彩色城市影像地图统一协调性研究

从认知地图和城市景观差异的角度分析了融合的基本原则,从地图色彩、美学的角度,提出可行的影像预处理以及道路和符号的设计方案,有效地提高了影像地图的统一协调性.     

Amplitude Preserving Kirchhoff Migration: A Traveltime Based Strategy

Amplitude versus offset information is a key feature to seismic reservoir characterization. Therefore amplitude preserving migration was developed to obtain this information from seismic reflection data. For complex 3-D media, however, this process is computationally expensive. In this paper we present an efficient traveltime based strategy for amplitude preserving migration of the Kirchhoff type. Its foundations are the generation of traveltime tables using a wavefront-oriented ray-tracing technique, and a generalized moveout relation for 3-D heterogeneous media. All required quantities for the amplitude preserving migration are computed from coarsely gridded traveltime tables. The migration includes the interpolation from the coarsely gridded input traveltimes onto the fine migration grid, the computation of amplitude preserving weight functions, and, optionally, the evaluation of an optimized migration aperture. Since ray tracing is employed for the traveltime computation the input velocity model needs to be smooth, i.e. velocity variations of spatial dimensions below the wavelength of the considered reflection signals are removed. Numerical examples on simple generic models validate the technique and an application to the Marmousi model demonstrates its potential to complex media. The major advantage of the traveltime based strategy consists of its computational efficiency by maintaining sufficient accuracy. Considerable savings in storage space (10⁵ and more for 3-D data with respect to no interpolation at all) can be achieved. The computational time for the stack can be substantially reduced (up to 90% in 3-D) with the optimized migration aperture since only those traces are stacked which really contribute to the image point under consideration.     

Shaking table tests of 1:4 reduced‐scale models of masonry infilled reinforced concrete frame buildings

Two models of masonry infilled reinforced concrete frame buildings were tested at the shaking table. Models were built in the reduced scale 1:4 using the materials produced in accordance to modelling demands of true replica modelling technique. The first model represented a one‐storey box‐like building and the second one the two‐stories building with plan shaped in the form of a letter H. Models were shaken with the series of horizontal sine dwell motions with gradually increasing amplitude. Masonry infills of tested models were constructed of relatively strong bricks laid in weak mortar. Therefore, typical cracks developed and propagated along mortar beds without cracking of bricks or crushing of infill corners. Data collected from tests will be used in future evaluation, verification and development of computational models for prediction of in‐plane and out‐of‐plane behaviour of masonry infills. The responses of tested models can be well compared with global behaviour of real structures using the modelling rules. The similarity of local behaviour of structural elements, e.g. reinforced concrete joints, is less reliable due to limitations in modelling of steel reinforcement properties. The model responses showed that buildings designed according to Eurocodes are able to sustain relatively high dynamic excitations due to a significant level of structural overstrength. Copyright © 2001 John Wiley & Sons, Ltd.     

城市大比例尺真正射影像阴影与遮挡问题的研究

为解决城市大比例尺正射影像生成的问题,从真正射影像的关键技术入手,着重研究其中的阴影与遮挡问题并提出相应解决方法。将这些方法应用在美国丹佛城区的真正射影像生成的项目中,取得了令人满意的效果。     

真正射影像生成的遮蔽检测和纹理修复方法

针对真正射影像在生产中遮蔽检测和纹理修复的问题,该文提出了一种基于面元和投影方向自适应确定检测路径的高程遮蔽检测方法用于解决真正射影像生产中遮蔽区域的检测问题;提出了一种基于影像方位和建筑物倒向判断的遮蔽补偿方式,用于解决真正射影像生产中遮挡区域的纹理修复问题。实验表明,本文方法提高了真正射影像生产的精度和效率,遮蔽检测效率较普通的高程射线追踪方法可提高一个数量级以上。     

双模三维环境下的态势标绘技术研究

针对虚拟三维环境态势标绘存在精度低、交互操作难以控制的缺点,提出了一种双模三维环境下的态势标绘与显示技术。首先利用遥感正射影像和DEM制作立体辅助影像,构建由立体辅助影像对形成的真实三维环境,并将其与传统虚拟三维环境无缝集成;利用立体辅助影像的高精度量测的特性,在真实三维环境中精确采集态势符号定位点,根据标绘规范形成三维态势符号;最后在虚拟三维环境中进行态势的逼真显示。实验结果表明:双模三维环境下的态势标绘技术能够有效避免三维符号与地形之间的混叠,提高态势标绘精度,是高分辨率遥感卫星影像的一种新应用模式。     

光线追踪遮挡检测算法

遮挡检测是真正射影像制作中关键的一步。本文根据光线追踪法遮挡检测的原理,将TIN数据分为基本面三角网和墙面三角网分别进行遮挡检测,对格网数据则采用光线与DSM表面的高程差值的变化规律来确定遮挡关系,从而得到改进的遮挡检测算法。实验证明改进后的算法能够准确地检测出复杂建筑物的遮挡区域。特别是格网数据的光线追踪遮挡检测更简单、更有效。     

基于滤波及起算数据误差的验后估计法

针对起算数据具有误差时现有处理方法的缺陷,巧妙地利用了真值和估值之间的关系处理起算数据误差,提出了基于滤波的顾及起算数据误差的验后估计法,剔除了起算数据误差的影响,得出相对于起算数据误差基准的平差结果。平差计算与随机模型的验后估计同时进行,使数据处理得更加完善。