AutoCAD DXF图形的批量无损投影转换方法

详细研究AutoCADDXF图形数据文件结构,实现AutoCAD图形批量无损投影换带转换的有效技术方法,采用VB程序设计编程,开发配套应用程序,具有工程效益和推广价值。     

用logistic映射混沌点修正选权迭代法估计残差方法

选权迭代法获得的结果往往含有较大的残差,修正其残差是一个值得关注的问题.联系logistic映射产生混沌点的理论概率分布特点,用其产生的修正值,在L范数最小的条件下,逐次获得修正值.同时给出了测绘实际工作实践,模拟计算得到了较好的效果.     

一种新的球面三角投影:等角比投影(EARP)

设计一种面向球面三角形的新的投影--等角比投影(Equal Angle Ratio Projection,EARP),该投影包括平行以及同轴两种模式,支持正六面体、正八面体、正二十面体等柏拉图立体(Plato Polvhedron)[1～3]以及任意Voronoi球面三角剖分.可以选择任意形状的投影平面三角,投影坐标由球面弧角度与特征球面弧角度之比决定,弧线族上的均分点与2维投影面上均匀分布的三角网格顶点相对应.本文给出了该模型正八面体以及正二十面体(EARPIH)的具体方程式的求解,证明了基于QTM的GoodChild[4]和Otoo[5 ]的离散投影方程是该投影的两种特例,并探讨了面积比性质,发现EARPIH投影的面积比变动范围相对狭小.支持该投影的球面剖分模型的地理坐标与球面三角格网之间的坐标转换可转换为均分三角网格的计算问题.     

Observations on the extended Matsuoka–Nakai failure criterion

The equivalent Mohr–Coulomb (M‐C) friction angle ? (J. Geotech. Eng. 1990; 116 (6):986–999) of the extended Matsuoka–Nakai (E‐M‐N) criterion has been examined under all possible stress paths. It is shown that ? depends only on the ratio of cohesion to confining stress c^′/σ and the frictional angle ?, where ? is the friction angle measured in triaxial compression (or extension) to which the E‐M‐N surface is fitted. It is also shown that ? is independent of c^′, when σ=0 and of σ when c^′=0, with the former representing an upper bound and the latter a lower bound of ? for any particular stress path. The closest point projection method has also been implemented successfully with the E‐M‐N criterion, and plane strain and axisymmetric element tests performed to verify some theoretical predictions relating to failure and post‐yielding behavior. Finally, a bearing capacity problem was analyzed using both E‐M‐N and M‐C, highlighting the conservative nature of M‐C for different friction angles. Copyright © 2009 John Wiley & Sons, Ltd.     

Decreasing Arctic Sea Ice Mirrors Increasing CO2 on Decadal Time Scale

Arctic sea ice is a keystone indicator of greenhouse-gas induced global climate change, which is expected to be amplified in the Arctic. Here we directly compare observed variations in arctic sea-ice extent and CO2 since the beginning of the 20th century, identifying a strengthening linkage, such that in recent decades the rate of sea-ice decrease mirrors the increase in CO2, with r ~ –0.95 over the last four decades, thereby indicating that 90% (r2 ~ 0.90) of the decreasing sea-ice extent is empirically “accounted for” by the increasing CO2 in the atmosphere. The author presents an empirical relation between annual sea-ice extent and global atmospheric CO2 concentrations, in which sea-ice reductions are linearly, inversely proportional to the magnitude of increase of CO2 over the last few decades. This approximates sea-ice changes during the most recent four decades, with a proportionality constant of 0.030 million km2 per ppmv CO2. When applied to future emission scenarios of the Intergovernmental Panel on Climate Change (IPCC), this relationship results in substantially faster ice decreases up to 2050 than predicted by IPCC models. However, departures from this projection may arise from non-linear feedback effects and/or temporary natural variations on interannual timescales, such as the record minimum of sea-ice extent observed in September 2007.Citation: Johannessen, O. M., 2008: Decreasing arctic sea ice mirrors increasing CO2 on decadal time scale, Atmos. Oceanic Sci. Lett., 1, 51-56     

考虑实际投影成像平面位置的扇束滤波反投影(FFBP)算法

扇束滤波反投影(Fan-beam Filtered Back Projection- FFBP)算法理论公式中,投影成像平面位于旋转中心;而实际CT扫描系统中,投影成像平面与旋转中心都存在一定距离.考虑到实际投影成像平面位置,本文推导了它的FFBP算法(即IFFBP-Improved Fan-beam Filtered Back Projection算法),比较了此两种情况下(即忽略成像平面与旋转中心距离)FFBP、IFFBP算法重建质量.计算机模拟和实验结果证明了IFFBP算法的正确性.     

地图投影反解变换的一种新方法

通常地图投影反解变换有2种方法,即多项式拟合法和投影方程解析法.多项式法利用已知控制点的坐标对应关系,通过最小二乘法拟合求解地图投影反解变换的多项式函数,其优点是反解模型与地图投影无关,算法具有通用性,缺点是反算精度较低.解析法根据地图投影正算公式,在一定条件下通过解方程求得地图投影反解变换解析式,其优点是反解变换精度高,缺点是解法复杂.本文利用计算数学方法,根据地图投影变换的基本数学原理,提出了一种新的地图投影反解变换方法,双向迭代逼近法(BDIRA).具有反解变换精度高、收敛速度快、算法通用和GIS软件编程实现方便等特点.     

关于微分圆投影变成变形椭圆的分析与研究

针对各种地图学教材中关于变形椭圆的证明提出了三个问题,通过对地图投影中的微分圆垂直投影或 斜投影分析,不仅证明了微分圆投影变成了变形椭圆,而且利用几何分析解决了各种地图学教材中关于变形椭圆 证明出现的三个问题,对进一步了解地图投影的变形分布规律有着重要的意义。     

斜轴高斯投影在跨带物探长剖面测量中的应用

在高精度物探重力测量中,需要提供高精度的平面位置和高程。在物探长剖面测量中,对东西跨度较大的线路进行控制测量时,高斯-克吕格投影分带和高程引起的投影变形较大,不能满足长距离重力测量对精度的要求。基于高斯-克吕格投影的基本理论,采用斜轴变形椭球高斯投影方法,结合最小二乘法、坐标转换理论及椭球变换,将原始椭球构建斜轴变形椭球,可以减小高斯投影横坐标和高程投影变形的影响,避免高斯投影分带过多对应用的影响。以漠河—呼和浩特物探长剖面测地数据为例,利用GPS快速静态测量获得平面和高程位置,测点距离约1km,通过斜轴高斯投影进行投影,最大平面精度为67.87mm/km,最大高程精度为53.039mm/km,最大投影综合变形的中误差为88.51 mm/km,大大减小了投影变形,提高了地图投影精度。因此,该投影在跨度物探长剖面测量中的应用具有一定优势。     

Model Projections of Precipitation Minus Evaporation in China

Changes in precipitation minus evaporation (P -E) are analyzed to investigate the possible impacts of climate change on water resource conditions in China. Simulations of SRES A1B and 20C3M scenarios from the WCRP CMIP3 GCMs are employed in the study. Time slice analysis shows that there would be more annual mean P -E across China in 2040-2055 and 2080-2099, compared to 1980-1999, with the largest percentage change over Northwest China and the Bohai Rim area. Precipitation and evaporation would also increase over entire China during these two periods. Annual mean P -E, precipitation, and evaporation averaged over the whole China and its eight sub-areas all yield generally upward trends during the 21st century. This indicates that on annual mean scale, the global warming related precipitation dominates the hydroclimate conditions in China. On seasonal mean scale, although precipitation is projected to increase over China, P -E exhibits both decreasing and increasing trends over certain regions of China. This suggests that the variation of global warming related evaporation dominates hydroclimate conditions over some parts of China, especially in northern China. Therefore, in hydroclimate condition projections, considering both evaporation and precipitation changes should be more reasonable than considering only precipitation.