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881.
882.
Stien Heremans Bert Bossyns Herman Eerens Jos Van Orshoven 《International Journal of Applied Earth Observation and Geoinformation》2011
Artificial neural networks (ANNs) are a popular class of techniques for performing soft classifications of satellite images. They have successfully been applied for estimating crop areas through sub-pixel classification of medium to low resolution images. Before a network can be used for classification and estimation, however, it has to be trained. The collection of the reference area fractions needed to train an ANN is often both time-consuming and expensive. This study focuses on strategies for decreasing the efforts needed to collect the necessary reference data, without compromising the accuracy of the resulting area estimates. Two aspects were studied: the spatial sampling scheme (i) and the possibility for reusing trained networks in multiple consecutive seasons (ii). Belgium was chosen as the study area because of the vast amount of reference data available. Time series of monthly NDVI composites for both SPOT-VGT and MODIS were used as the network inputs. The results showed that accurate regional crop area estimation (R2 > 80%) is possible using only 1% of the entire area for network training, provided that the training samples used are representative for the land use variability present in the study area. Limiting the training samples to a specific subset of the population, either geographically or thematically, significantly decreased the accuracy of the estimates. The results also indicate that the use of ANNs trained with data from one season to estimate area fractions in another season is not to be recommended. The interannual variability observed in the endmembers’ spectral signatures underlines the importance of using up-to-date training samples. It can thus be concluded that the representativeness of the training samples, both regarding the spatial and the temporal aspects, is an important issue in crop area estimation using ANNs that should not easily be ignored. 相似文献
883.
884.
建立高精度、高分辨率的区域似大地水准面模型是GPS高程测量在实际应用中必须解决的首要问题,分别介绍BP神经网络、曲面拟合的模型及算法,并基于焦作市GPS测量数据,通过MATLAB编程计算和分类实验,验证几种算法的有效性与可靠性,结果证明神经网络算法要优于其它算法,最后给出有益的结论. 相似文献
885.
Acquisition and registration of terrestrial 3D laser scans is a fundamental task in mapping and modeling of cities in three dimensions. To automate this task marker-free registration methods are required. Based on the existence of skyline features, this paper proposes a novel method. The skyline features are extracted from panoramic 3D scans and encoded as strings enabling the use of string matching for merging the scans. Initial results of the proposed method in the old city center of Bremen are pre-sented. 相似文献
886.
Car routing solutions are omnipresent and solutions for pedestrians also exist.Furthermore,public or commercial buildings are getting bigger and the complexity of their internal structure has increased.Consequently,the need for indoor routing solutions has emerged.Some prototypes are available,but they still lack semantically-enriched modelling (e.g.,access constraints,labels,etc.) and are not suitable for providing user-adaptive length-optimal routing in complex buildings.Previous approaches consider simple rooms,concave rooms,and corridors,but important characteristics such as distinct areas in huge rooms and solid obstacles inside rooms are not considered at all,although such details can increase navigation accuracy.By formally defining a weighted indoor routing graph,it is possible to create a detailed and user-adaptive model for route computation.The defined graph also contains semantic information such as room labels,door accessibility constraints,etc.Furthermore,one-way paths inside buildings are considered,as well as three-dimensional building parts,e.g.,elevators or stairways.A hierarchical structure is also possible with the presented graph model. 相似文献
887.
本文主要介绍了三维模型数据的内容,分析了基于数字摄影测量方式的三维模型数据的质量分析与控制,并总结了实际生产过程中特殊问题的处理方法。 相似文献
888.
主要介绍了数字城市中地上、地下数据的管理以及3维可视化技术,对地上地下场景进行了综合比较,讨论了地上地下3维一体化的表现思想,精确的表现地形地貌、地上建筑、地下管线分布,让设计人员和决策者可以在宏观层面把握城市空间形态的要点和亮点,体现城市特色. 相似文献
889.
主要研究了3维城市模型的相关理论与技术,提出了拓扑关系、尺度及可视化等问题,讨论了3维城市模型的建设方法及关键技术,并对3维城市模型的发展进行了展望。 相似文献
890.
Pictometry倾斜摄影技术及其在3维城市建模中的应用 总被引:4,自引:0,他引:4
倾斜摄影技术是国际测绘领域近些年发展起来的一项高新技术.它颠覆了以往正射影像只能从垂直角度拍摄的局限,通过在同一飞行平台上搭载多台传感器,同时从一个垂直、四个倾斜等五个不同的角度采集影像,将用户引入了符合人眼视觉的真实直观世界.倾斜影像技术的引进和应用,使得目前高昂的3维城市建模成本将得以大大降低.由于倾斜影像为用户提... 相似文献