3维模型检索的特征提取技术分析

首先介绍了一个完整的3维模型检索系统的研究内容,然后对其中的关键技术3维模型特征提取方法中的统计特征提取方法、骨架提取方法、基于几何学的提取方法进行了分析比较。最后提出了3维模型检索技术今后需要研究的一些问题。     

Applications of Lodrigues Matrix in 3D Coordinate Transformation

Three transformation models (Bursa-Wolf, Molodensky, and WTUSM) are generally used between two data systems transformation. The linear models are used when the rotation angles are small; however, when the rotation angles get bigger, model errors will be produced. In this paper, we present a method with three main terms: ① the traditional rotation angles θ , φ ,ψ are substituted with a , b, c which are three re-spective values in the anti-symmetrical or Lodrigues matrix; ② directly and accurately calculating the formula of seven parameters in any value of rotation angles; and ③ a corresponding adjustment model is established. This method does not use the triangle function. Instead it uses addition, subtraction, multiplication and division, and the complexity of the equation is reduced, making the calculation easy and quick.     

基于BP神经网络的三维激光测高数据拟合方法

针对三维激光测高拟合问题，本文采用BP神经网络进行拟合，该方法可以有效地消除或减弱数据中的系统误差影响，提高计算精度。实际算例证明，在数据无粗差情况下，BP神经网络的内符合与外符合精度优于传统的二次曲面拟合的精度。     

基于面向对象技术的3D量测系统

本文主要阐述可量测立体像对的3D坐标量测系统的设计与实现。由于现存的全数字摄影测量产品要么是价格非常高昂的高端专业设备（一般为具有高端图像卡的工作站），要么是功能受约束的简单设备。本文将说明如何在非高端图形PC设备上，运用面向对象程序设计、软件模块化和硬件无关性等技术实现所要求的立体量测系统功能。     

斜拉桥索塔三维相对基准定位方法研究

结合斜拉桥索塔基准放样及斜拉索预埋钢管的精密定位的需要，提出了一种新的基于测量机器人的三维相对基准放样方法，并成功用于灌河特大桥斜拉桥主桥的施工放样。实践证明，与传统的方法相比，该方法具有方便、高效、精度高等特点。     

3S集成技术在城镇土地利用变更调查中的应用研究

城镇地区由于建筑物密集、土地利用类型变化快、土地利用现状图比例尺较大等特点,土地利用变更调查主要依靠专业部门利用全站仪完成,但全站仪需要通视的特点限制了其工作效率。而采用3S集成技术进行城镇地区土地利用变更调查的技术方法,则可以相应提高工作效率。基于3S集成技术城镇地区土地利用变更调查的应用模式为:通过GPS接收机与笔记本电脑(已配置GIS软件系统)通讯,实现GPS与GIS的集成,并调用RS影像作为底图,既可实现实时的数据采集、存储和编辑。对于城镇地区部分GPS信号弱的地区,采用测边交会的方法则可以完成这些点的数据采集,克服了GPS使用盲区的限制。     

激光法气相合成纳米Si/C/N复相粉体

用大功率５ｋＷＣＯ２激光器为能源,以六甲基二硅胺烷［（ＣＨ３）３Ｓｉ］２ＮＨ（简称ＨＭＤＳ）和ＮＨ３为原料,合成纳米非晶Ｓｉ／Ｃ／Ｎ复相粉体。研究了ＨＭＤＳ流量和ＮＨ３对纳米复相粉体组成的影响。ＮＨ３的加入可以大幅度降低纳米复相粉体的碳含量,提高氮含量。Ｓｉ／Ｃ／Ｎ纳米复相粉体的粒径分布范围为１０～５０ｎｍ,为非晶态。     

Three-dimensional geometrical ray theory and modelling of transmitted seismic energy of data from the Nevada Test Site

This paper presents a geometrically based algorithm for computing synthetic seismograms for energy transmitted through a 3-D velocity distribution. 3-D ray tracing is performed to compute the traveltimes and geometrical spreading (amplitude). The formulations of both kinematic and dynamic ray-tracing systems are presented. The two-point ray-tracing problem is solved by systematically updating the initial conditions and adjusting the ray direction until the ray intersects the specified endpoint. The amount of adjustment required depends on the derivatives of the position with respect to the given starting angles between consecutive rays. The algorithm uses derivatives to define the steepest-descent direction and to update the initial directions. The convergence rate depends on the complexity of the model.
Test seismograms compare favourably with those from a 2-D asymptotic ray theory algorithm and a 3-D Gaussian-beam algorithm. The algorithm is flexible in modelling arbitrary source and recorder geometries for various smoothly varying 3-D velocity distributions. The algorithm is further tested by simulating surface-to-tunnel vibroseis field data. Shear waves as well as compressional waves may be approximately included. Application of the algorithm to a data set from the Rainier Mesa of the Nevada Test Site produced a good fit to the transmitted (first arrival) traveltimes and amplitudes, with approximately 15 per cent variation in the local 3-D velocity.     

Oxygen isotope fractionation in mantle minerals

The increment method is adopted to calculate oxygen isotope fractionation factors for mantle minerals, particularly for the polymorphic phases of MgSiO₃ and Mg₂SiO₄. The results predict the following sequence of¹⁸O-enrichment:pyroxene (Mg, Fe, Ca)₂Si₂O₆>olivine (Mg, Fe)₂SiO₄ > spinel (Mg, Fe)₂SiO₄> ilmenite (Mg, Fe, Ca) SiO₃>perovskite (Mg, Fe, Ca) SiO₃. The calculated fractionations for the calcite-perovskite (CaTiO₃) System are in excellent agreement with the experimental calibrations. If there would be complete isotopic equilibration in the mantle, the spinel-structured silicates in the transition zone are predicted to be enriched in¹⁸O relative to the perovskite-structured silicates in the lower mantle but depleted in¹⁸O relative to olivines and pyroxenes in the upper mantle. The oxygen isotope layering of the mantle might result from differences in the chemical composition and crystal structure of mineral phases at different mantle depths. Assuming isotopic equilibrium on a whole earth scale, the chemical structure of the Earth’s interior can be described by the following sequence of¹⁸O-enrichment:upper crust>lower crust>upper mantle>transition zone>lower mantle>core. Project supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences.     

北京天文台的WET三通道高速光度计

对北京天文台新近改造成的三通道高速光度计的结构和性能进行介绍,并给出了在兴隆站85公分望远镜的一些实测结果.