Directed lines are fundamental geometric elements to represent directed linear en-tities. The representations of their topological relations are so different from those of simple lines that they cannot be solved exactly with normal methods. In this paper,a new model based on point-set topology is defined to represent the topo-logical relations between directed lines and simple geometries. Through the inter-sections between the start-points,end-points,and interiors of the directed lines and the interiors,boundaries,and exteriors of the simple geometries,this model identifies 5 cases of topological relations between directed lines and points,39 cases of simple lines,and 26 cases of simple polygons. Another 4 cases of simple lines and one case of simple polygons are distinguished if considering the exteri-ors of the directed lines. All possible cases are furthermore grouped into an exclu-sive and complete set containing 11 named predicts. And the conceptual neigh-borhood graph is set up to illustrate their relationship and similarity. This model can provide a basis for natural language description and spatial query language to present the dynamic semantics of directed lines relative to the background fea-tures.
GAO Yong1,ZHANG Yi1,TIAN Yuan1 & WENG JingNong2 1 Institute of Remote Sensing and Geographic Information System,Peking University,Beijing 100871,China
Constrained Delaunay Triangular Irregular Networks (CD-TIN),a kind of special data structure,have many practical applications in Geoinformatics,especially in the representation of linear constrained triangulation for DTM and DSM,such as in digital city and digital mine. Past researches on D-TIN mainly focused on point in-sertion and deletion without consideration of constraint,and that on CD-TIN usu-ally paid more attention to the insertion algorithms for points and edges,but little to the deletion algorithms. The presented algorithms are far insufficient for the dy-namic updating of CD-TIN. In this paper,the constraint edge in CD-TIN is consid-ered to be any set of broken lines,i.e.,polygon edges,broken lines and simple segments. The constraint edge may be composed of one or more constraint seg-ments,and it is allowed to be in any form: Open or close,intersection or self-in-tersection. By improving to present insertion and deletion algorithms for D-TIN,two new algorithms for CD-TIN updating are presented. According to the polymorphism of the constraints in CD-TIN,virtual point is adopted to represent the crossing node between constraint edges when a constraint edge is inserted in CD-TIN. Two new algorithms named as Integral Ear Elimination (IEE) and Influence Domain Retrian-gulation for Virtual Point (IDRVP) are presented,the former is for constraint point deletion,while the later is for the insertion and deletion of constraint edge. The principle of IDRVP is that to divide the influence domain of a virtual point into some parts by the constraint-keeping edges,and to retriangulate each part of the influ-ence domain individually referring to the constraint visible property and constraint empty circle (CEC) criterion. Finally,a prototype system is developed with VC++,one case on the integration of 3D terrain and buildings is demonstrated to test the correctness of new algorithms. It shows that the new algorithms are effective for the updating of CD-TIN.
WU LiXin1,2,WANG YanBing2,3 & SHI WenZhong2,4 1 Institute for Geo-informatics & Digital Mine Research,Northeastern University,Shenyang 110004,China
Digital Earth has been a hot topic and research trend since it was proposed,and Digital China has drawn much attention in China.As a key technique to implement Digital China,grid is an excellent and promising concept to construct a dynamic,inter-domain and distributed computing environment.It is appropriate to process geographic information across dispersed computing resources in networks effectively and cooperatively.A distributed spatial computing prototype system is designed and implemented with the Globus Toolkit.Several important aspects are discussed in detail.The architecture is proposed according to the characteristics of grid firstly,and then the spatial resource query and access interfaces are designed for heterogeneous data sources.An open-up hierarchical architecture for resource discovery and management is represented to detect spatial and computing resources in grid.A standard spatial job management mechanism is implemented by grid service for convenient use.In addition,the control mechanism of spatial datasets access is developed based on GSI.The prototype system utilizes the Globus Toolkit to implement a common distributed spatial computing framework,and it reveals the spatial computing ability of grid to support Digital China.
WU Lun,YAN MengLong,GAO Yong,YANG ZhenZhen,ZHAO Yong & CHEN Bin Institute of Remote Sensing and Geographic Information System,Peking University,Beijing 100871,China
A wiki system is a typical Web 2.0 application that provides a bi-directional platform for users to collaborate and share much useful information online.Unfortunately,computers cannot well understand the wiki pages in plain text.The user-generated geographical content via wiki systems cannot be manipulated properly and efficiently unless the geographical semantics is explicitly represented.In this paper,a geographical semantic wiki system,Geo-Wiki,is introduced to solve this problem.Geo-Wiki is a semantic geographical knowledge-sharing web system based on geographical ontologies so that computers can parse and storage the multi-source geographical knowledge.Moreover,Geo-Wiki mashed up with map services enriches the representation and helps users to find spatial distribution patterns,and thus can serve geospatial decision-making by customizing the Google Maps APIs.
GAO Yong,GAO Song,LI RunQiang & LIU YuInstitute of Remote Sensing and Geographical Information Systems,Peking University,Beijing 100871,China
Landslide susceptibility mapping is a typical two-class classification problem where generating pseudo absence (non-slide) data plays an important role.In this paper,a new method,target space exteriorization sampling method (TSES),is presented to generate pseudo absence data based on presence data directly in feature space.TSES exteriorizes a presence sample to become a pseudo absence one by replacing the value of one of its features with a new one outside the value range of this feature of all presence data.This method is compared with two existing methods,buffer controlled sampling (BCS) and iteratively refined sampling (IRS),in a study area of Shenzhen city.The pseudo absence data generated by each of these three methods are organized into 20 subsets with increasing data sizes to study the effects of the proportion of pseudo absence data to presence data.The landslide susceptibility maps of the study area are calculated with all these datasets by general additive model (GAM).It can be concluded that,through a 10-fold validation,TSES and IRS-based models have similar AUC values that are both greater than that of BCS,but TSES outperforms BCS and IRS in prediction efficiency.TSES results also have more reasonable spatial and histogram distributions than BCS and IRS,which can support categorization of an area into more susceptibility ranks,while IRS shows a tendency to separate the whole study area into two susceptibility extremes.It can be also concluded that when using BCS,the pseudo absence data proportion to the presence data would be about 50% to get a considerable result,while for IRS or TSES the minimum proportion is 40%.
With the rapid development of Internet,much spatial information contained in non-structured or semi-structured documents is available on the World Wide Web.In such documents,localities are always textually described using spatial relationships and named places,instead of numerical coordinates.Hence,extracting positional information from locality descriptions is an important task.In this paper,we bridge two aspects of locality descriptions,namely generating locality descriptions and positioning localities,and provide a method to compute probability density according to the selection probability of a reference object to describe the position of the target object.Refinement operation on uncertainty field is used to deal with locality description involving multiple reference objects.Three metrics are introduced to measure the results of positioning localities.We choose the mixed selection probability function based on Euclidean distance and Voronoi stolen-area to compute probability density function.Finally,we use three cases to demonstrate the proposed methods.
GONG YongXi 1,2,3,LI GuiCai 1,LIU Yu 2 & YANG Jian 1 1 Shenzhen Key Lab of Recycling Economy,Peking University Shenzhen Graduate School,Shenzhen 518055,China
