A graph edit dictionary for correcting errors in roof topology graphs reconstructed from point clouds

In the task of 3D building model reconstruction from point clouds we face the problem of recovering a roof topology graph in the presence of noise, small roof faces and low point densities. Errors in roof topology graphs will seriously affect the final modelling results. The aim of this research is to automatically correct these errors. We define the graph correction as a graph-to-graph problem, similar to the spelling correction problem (also called the string-to-string problem). The graph correction is more complex than string correction, as the graphs are 2D while strings are only 1D. We design a strategy based on a dictionary of graph edit operations to automatically identify and correct the errors in the input graph. For each type of error the graph edit dictionary stores a representative erroneous subgraph as well as the corrected version. As an erroneous roof topology graph may contain several errors, a heuristic search is applied to find the optimum sequence of graph edits to correct the errors one by one. The graph edit dictionary can be expanded to include entries needed to cope with errors that were previously not encountered. Experiments show that the dictionary with only fifteen entries already properly corrects one quarter of erroneous graphs in about 4500 buildings, and even half of the erroneous graphs in one test area, achieving as high as a 95% acceptance rate of the reconstructed models.     

立体测图数据在AutoCADMap3D中的自动预处理

从各种常用的摄影测量工作站的比较分析出发,针对原来的数字摄影测量工作站所生产的立体测图数据给后期数据编辑工作带来的数据拓扑问题,进行数据分析,并结合实际工作经验,给出一种在AutoCADMap3D软件中进行编辑前自动预处理的方法,以供读者参考。     

Planar and non-planar topologically consistent vector map simplification

This article contains a mathematical analysis of strategies for determining topological consistency of vector map simplifications. Such techniques exploit assumptions that can be made regarding the similarity of corresponding objects in successive simplifications. We propose that all topological relationships may be classified as planar or non-planar. A formal analysis of techniques for determining topological consistency of a simplification in terms of such relationships is presented. For each technique we analyse any corresponding constraints that are imposed. This provides a unified understanding of the benefits and limitations of individual techniques and the relationships that exist between techniques. Subsequently, a new strategy for determining the topological consistency of a simplification is proposed. This technique integrates the benefits all methods studied to provide a solution which is subject to less constraints. The effectiveness of this approach is demonstrated through fusion with an existing simplification technique resulting in simplifications that have equal topology and similar shaped features to the original map.     

利用双重索引快速构建道路网络连通拓扑

路网拓扑关系的生成是进行最优路径规划的基础。本文针对ISO GDF4.0模型对道路连通拓扑的定义,结合最优路径规划对道路网络连通拓扑的要求,提出一种使用R-tree空间索引和B-tree索引双重索引方式快速生成道路连通拓扑的算法。连通拓扑快速构建算法包括新道路生成和网络拓扑提取两部分,新道路生成过程中,首先,自上而下地打断道路形成直线段集并求交点,然后,自下而上地重构直线段集以生成新道路。在打断道路求交点过程中,对道路建立R-tree空间索引,显著提高了几何要素的查找速度。在网络拓扑提取过程中对序列化数据建立B-tree索引,使得其查找速度大大加快。通过对双重索引算法的时间复杂度分析与验证表明,本文提出的拓扑生成算法具有较高的执行效率。     

面状水系伪增量剔除的拓扑量化法

针对定量过滤法剔除伪增量时存在的真增量被过度过滤、伪增量不能完全过滤等缺陷,结合国家1∶5万数据库更新工程的实际需求,提出一种新的伪增量剔除方法——拓扑量化法,主要思想是结合拓扑空间关系判断与缓冲区量化分析来识别伪增量,进而得到更加准确的增量信息。     

利用BP网络识别点状地图符号的研究

在利用BP网络识别点状地图符号的过程中,提出了三项改进措施,简化了数据获取,提高了网络收敛速度。通过对训练样本图像的格式分析,实现了输入神经元的简单获取;对神经元、权值数组采取堆内存动态分配的方式,减少了内存占用,极大地提高了权收敛速度;通过对网络拓扑的分析,调整了节点的输出方式,加快了权值改正。     

基于GDF的道路网完全拓扑生成算法

拓扑关系生成是导航空间数据库构建的一个关键环节。该文根据ISOGDF4.0的要求和道路网拓扑关系的特点,研究了一种道路网完全拓扑关系的生成算法,即根据点的几何坐标生成结点—边拓扑关系的算法,以及从标识点出发利用Qi算子生成部分非传统面拓扑关系的算法。实验表明,此算法的时间效率较高,特别是部分面拓扑关系的定义及生成算法能满足实际导航应用的需要。     

地籍测量信息处理系统若干问题的探讨

简要介绍了信息时代对地籍信息的要求和地籍信息的拓扑结构，探讨了如何实现地籍测量信息处理系统与GIS系统的无缝结合。