基于调制方案的抗投影变换数字水印算法     

杨辉  闵连权  侯翔 《测绘科学》2015,40(4):19-22

针对传统数字水印算法无法抵抗投影变换攻击的问题,该文提出了一种对投影变换具有较高鲁棒性的数字水印算法。结合投影变换具有拓扑关系不变性以及在小范围内近似等特点,该文选择定位点和经纬线网格之间的包含关系作为水印载体,通过修改包含关系嵌入水印。实验证明该方法不仅对多种投影变换具有鲁棒性,而且能够抵抗裁剪、压缩等常见攻击,算法能够有效提高对矢量地图数据版权保护的能力。  相似文献   

基于仿射变换的线状符号绘制算法研究     

王继周  赵占杰  孙伟 《测绘科学》2015,40(7):92-97

针对目前线状符号绘制方法在转折处无法很好地保证复杂图元的几何关系,从而影响显示效果的问题,该文提出一种基于仿射变换的线状符号绘制算法,解决了在保证任意复杂符号的几何拓扑关系不变情况下转折处的平滑过渡难题,实现了线状符号的高效、美观绘制。最后经实际应用验证,该方法能够满足地理信息系统符号化显示和计算机制图需求。  相似文献   

一种基于边界搜索的栅格矢量化算法     

魏金标  陈振杰  周琛  任沂斌 《测绘科学》2015,40(3):115-118

栅格数据的矢量化是GIS领域重要的研究内容。针对栅格数据矢量化准确率低和效率低等问题,该文提出了一种基于边界搜索的矢量化算法,通过对栅格图像的一次遍历,提取结点和中间点,生成弧段,构建多边形;并在构建多边形中,提出了一种简单易行的最右侧方向判断方法,综合运用最小外接矩形和射线法判定逆时针多边形的归属。实验表明,该文提出的矢量化算法能够较准确矢量化复杂的栅格图像,具有较好的效率,可为多值栅格图像快速矢量化及相关研究提供借鉴。  相似文献   

Correlation －SVM 模型在大坝变形预测中的应用     

朱涛  刘慕溪 《测绘与空间地理信息》2015,(8):37-40

引起大坝变形的影响因素很多,即在利用支持向量机（ SVM）模型进行大坝变形分析和预报的过程中,需要将所有的影响因子都输入到SVM模型中,这样会造成输入因子的不侧重性,基于此,本文对大坝变形的影响因子进行相关性分析,根据大坝变形影响因子和大坝变形量之间的关系来确定最优的影响因子,即将比重比较大的影响因子输入到SVM模型中,从而提高了SVM模型运行效率及预测的精度和速度。  相似文献   

基于地理视角的智慧城市规划与建设的理论思考   总被引：8，自引：4，他引：4  

甄峰  席广亮  秦萧 《地理科学进展》2015,34(4):402-409

智慧城市建设是推动城镇化发展的重要动力,其建设除了技术支撑之外,还应充分考虑信息技术对城市政府、企业和居民活动及其空间的影响。本文在对国内智慧城市建设现状与问题分析思考的基础上,认为智慧城市的出现是适应当前城市化战略转型、公共服务提升、社区发展和城市问题解决的必然趋势,从多源异构数据整合、信息系统和空间分析平台两个方面梳理智慧城市建设的关键技术,从流动空间以及新的人地关系、时空协调发展等方面提出智慧城市的理论支撑,并进一步明确地理学应对和研究重点。同时,提出基于城市地理研究的智慧城市规划与建设实践的主要方向,包括顶层设计、功能和空间布局、基础设施整合、城乡治理等内容。  相似文献   

Specific Relationship between the Surface Air Temperature and the Area of the Terra Nova Bay Polynya,Antarctica   总被引：1，自引：0，他引：1  

Yifan DING  Xiao CHENG  Xichen LI  Mohammed SHOKR  Jiawei YUAN  Qinghua YANG  Fengming HUI 《大气科学进展》2020,37(5):532-544

Antarctic polynyas play an important role in regional atmosphere?ice?ocean interactions and are considered to help generate the global deep ocean conveyer belt.Polynyas therefore have a potential impact on the Earth’s climate in terms of the production of sea ice and high-salinity shelf water.In this study,we investigated the relationship between the area of the Terra Nova Bay polynya and the air temperature as well as the eastward and northward wind based on the ERA5 and ERAInterim reanalysis datasets and observations from automatic weather stations during the polar night.We examined the correlation between each factor and the polynya area under different temperature conditions.Previous studies have focused more on the effect of winds on the polynya,but the relationship between air temperature and the polynya area has not been fully investigated.Our study shows,eliminating the influence of winds,lower air temperature has a stronger positive correlation with the polynya area.The results show that the relationship between the polynya area and air temperature is more likely to be interactively influenced.As temperature drops,the relationship of the polynya area with air temperature becomes closer with increasing correlation coefficients.In the low temperature conditions,the correlation coefficients of the polynya area with air temperature are above 0.5,larger than that with the wind speed.  相似文献   

An Empirical Tropical Instability Wave-induced Wind Stress Model in the Equatorial Pacific and its Incorporation into the Ocean Model     

Yanzhou Wei  Xianbiao Kang  Yuhua Pei 《大气与海洋》2013,51(5):350-361

Abstract

Satellite observations revealed that there is a close relationship between perturbations of sea surface temperature (SST) and wind stress (τ) induced by tropical instability waves (TIWs; SST_TIW and τ _TIW). Using the empirical relationship observed between TIW-induced wind stress divergence (curl) and downwind (crosswind) SST gradients, this study establishes a TIW-induced wind stress field perturbation model τ _TIW?=?F(SST). This empirical model solves τ _TIW from the TIW-induced wind stress divergence and curl, which are estimated from the downwind and crosswind SST gradients. This empirical τ _TIW?=?F(SST) model can be incorporated into the ocean model to take into account the effect of τ _TIW. By comparing two experiments with and without the τ _TIW effect, this study demonstrates that τ _TIW has a substantial effect on the equatorial Pacific heat budget and induces the long-term mean SST to exhibit a 0.2°C difference, which is consistent with previous studies.  相似文献   

统计方法与淹没模型结合的山洪灾害风险评估方法及其应用   总被引：1，自引：0，他引：1  

张容焱  游立军  高建芸  林昕  唐振飞 《气象》2013,39(12):1642-1648

本文针对有水位资料,但没有流量观测的流域,同时又有历史罕见洪水记载、流域断面洪水警戒水位和自动站记载的近年几次小洪水过程,采用统计分析方法确定雨 洪关系,得到致灾临界雨量;再应用淹没模型模拟洪水淹没情况,得到洪水的风险等级评估。通过对历史特大山洪个例的淹没反演,可以看到由数理统计与淹没模型相结合的方法确定出的山洪风险等级,与实际情况基本相符。由于洪水记载和考察资料,往往对洪水淹没的高度记录准确,而对发生的具体时间通常是模糊的,本文得到的临界雨量指标是否能够预见洪水需要实例检验。通过2012年前汛期强降水过程的检验,虽然预警了低风险洪水事件,但是风险发生时间有差异,经过合理调整低风险临界雨量,满足了能够预见洪水的目的。对于其他等级的临界雨量的检验,有待于日后更多的实例,进行合理的调整,逐步完善翠江流域的山洪临界雨量指标。  相似文献   

国家资源环境安全要素的综合评价   总被引：5，自引：0，他引：5  

张雷 《地球信息科学学报》2002,4(4):86-92

资源环境安全问题始终是世界各国持续发展的核心任务和基本需求。考虑到单要素和整体两大分析方法的不足 ,作者提出了一种具有针对性的要素综合分析方法。根据世界 10个人口 1亿以上国家的抽样分析表明 ,土地、水资源、矿产及生态环境的整体状态是决定国家资源环境安全的基本要素群体。与此同时 ,为了改善国家 ,特别是发展中国家的资源环境脆弱状态和提高其稳定程度 ,第一是严格控制人口增长 ;第二是努力推进本国资源环境开发的国际化进程 ;第三是增大智力投入以提高资源深化加工程度 ;第四是加大本国生态环境保护力度。  相似文献   

An approximated method for the solution of elliptic problems in thin domains: Application to nonlinear internal waves     

A. Scotti  S. Mitran   《Ocean Modelling》2008,25(3-4):144-153

Realistic numerical simulations of nonlinear internal waves (NLIWs) have been hampered by the need to use computationally expensive nonhydrostatic models. In this paper, we show that the solution to the elliptic problem arising from the incompressibility condition can be successfully approximated by a few terms (three at most) of an expansion in powers of the ratio (horizontal grid spacing)/(total depth). For an n dimensional problem, each term in the expansion is the sum of a function that satisfies a one-dimensional second-order ODE in the vertical direction plus, depending on the surface boundary condition, the solution to an n-1 dimension elliptic problem, an evident saving over having to solve the original n-dimensional elliptic problem. This approximation provides the physically correct amount of dispersion necessary to counteract the nonlinear steepening tendency of NLIWs. Experiments with different types of NLIWs validate the approach. Unlike other methods, no ad hoc artificial dispersion needs to be introduced.  相似文献