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减少数据量将为减少计算机数据储存空间和数据处理时间提供许多便利。本文描述了一种三维数字高程数据压缩过程，文章首先简要地概述了数字地形数据获取的某些方法，与实际试验一起，详细描述了这种新的 过程，提供了本文所建议的算法与目前备择算法的比较研究结果。 相似文献
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Organochlorine pesticide residues in sediments and biota from the coastal area of Dar es Salaam city,Tanzania 总被引：1，自引：0，他引：1
Sediment and biota samples were collected from Msimbazi and Kizinga rivers and from the coastal marine environment of Dar es Salaam during both dry and wet seasons. The samples were analyzed for various organochlorine pesticide residues using GC-ECD and GC-MS. Dieldrin, p,p′-DDT, p,p′-DDE, p,p′-DDD, o,p′-DDT and γ-HCH were detected at significantly greater concentrations above the method detection limits. Recoveries of pesticide residues ranged 86.5–120% in sediments and 62–102% in biota. The average concentrations of total DDT in sediments for the two seasons were almost the same. Biota samples showed significant difference in levels of residues depending on mode of feeding and age of analyzed biota. p,p′-DDT to total DDT ratios in all matrices indicated recent use of DDT. The levels of residues in sediments suggest possible adverse effects to humans consuming biota that are directly exposed to the sediments. This effect, which is associated with bio-concentration of residues in the tissues of edible aquatic biota, should not affect wildlife. In spite of concern on the adverse effect to humans posed by pesticide residues in sediments, edible biota from the examined water bodies were found to be safe for human consumption. 相似文献
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本文考察了地理信息系统（ＧＩＳ）用户界面问题，概述了现行界面的不足，定义了从数据库到用户相关的通用语言界面（如ＵＧＩＸ），数据库通讯方法以及与这种交互形式相应的屏幕提示，本文认为ＧＩＳ界面应当是符合用户习惯并且以结构查询语言（ＳＱＬ）高级空间扩展形式为基础，这种结构有可能在现有的空间数据库上执行ＵＧＩＸ。 相似文献
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城市信息系统是城市工程及资源规划、开发与管理决策者受益的经济资源。本研究建立了基于城市地理信息系统（ＵＧＩＳ）原型的设计模型，开发该系统所需的基本图及视觉属性由航片获取。本研究使用了沙特阿拉伯首都中的一个新区，所建的模型对城市的某一应用（人口估计）是实用的。对特殊应用的测试结果表明：该系统具有满意的精度，并且在人口及社会特征类似的国家、城市也具有很好的应用前景。 相似文献
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Effective tools for monitoring the status of ecological restoration projects are critical for the management of restoration programs. Such tools must integrate disparate data comprised of multiple variables that describe restoration status, including the condition of environmental stressors, landscape connectivity, ecosystem resilience, and ecological structure and function, while communicating these concepts effectively to a wide range of stakeholders. In this paper we describe the process of constructing multimetric indices (MMIs) for monitoring restoration status for restoration projects currently underway on the eastern coast of Saudi Arabia. During this process, an initial suite of measurements is filtered for response and sensitivity to ecosystem stressors, eliminating measurements that provide little information and reducing future monitoring efforts. The retained measurements are rescaled into comparable domain metrics and assembled into MMIs. The MMIs are presented in terms of established restoration theories, including restoration trajectory and restoration endpoint targets. 相似文献
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