Faculty of Geosciences and Environmental EngineeringSouthwest Jiaotong University
Faculty of Geosciences and Environmental EngineeringSouthwest Jiaotong University
Nanyang Technological University
The Chinese University of Hong Kong
The Hong Kong Polytechnic University
Southwest Jiaotong University
Surveying and Mapping
North Jiaotong University
Southwest Jiaotong University
Southwest Jiaotong University
Virtual Geographic Environments (VGEs) are proposed as a new generation of geographic analysis tool to contribute to human understanding of the geographic world and assist in solving geographic problems at a deeper level. The development of VGEs is focused on meeting the three scientific requirements of Geographic Information Science (GIScience) — multi-dimensional visualization, dynamic phenomenon simulation, and public participation. To provide a clearer image that improves user understanding of VGEs and to contribute to future scientific development, our research group is now focusing on some aspects of VGEs.
Generally, three major aspects are studied by our group: digital photogrammetry, multi-dimensional dynamic GIS and the Virtual Geographic Environments.
Prof. Zhu has supervised more than 50 Ph.D students, more than 100 masters and 5 postdocs, among which Li Yuan has won the best youth paper on the 2008 ISPRS Congress, the Ph.D dissertation of Dr. Bo Wu has been nominated as the best 100 Ph.D in 2008 and Dr. Tarek has won the scholarship of overseas students in 2008.
The filtering of point clouds is a ubiquitous task in the processing of airborne laser scanning (ALS) data; however, such filtering processes are difficult because of the complex configuration of the terrain features. The classical filtering algorithms rely on the cautious tuning of parameters to handle various landforms. To address the challenge posed by the bundling of different terrain features into a single dataset and to surmount the sensitivity of the parameters, in this study, we propose an adaptive surface filter (ASF) for the classification of ALS point clouds. Based on the principle that the threshold should vary in accordance to the terrain smoothness, the ASF embeds bending energy, which quantitatively depicts the local terrain structure to self-adapt the filter threshold automatically. The ASF employs a step factor to control the data pyramid scheme in which the processing window sizes are reduced progressively, and the ASF gradually interpolates thin plate spline surfaces toward the ground with regularization to handle noise. Using the progressive densification strategy, regularization and self-adaption, both performance improvement and resilience to parameter tuning are achieved. When tested against the benchmark datasets provided by ISPRS, the ASF performs the best in comparison with all other filtering methods, yielding an average total error of 2.85% when optimized and 3.67% when using the same parameter set.
This paper proposes a reliable feature point matching method for oblique images using various spatial relationships and geometrical information for the problems resulted by the large view point changes, the image deformations, blurring, and other factors. Three spatial constraints are incorporated to filter possible outliers, including a cyclic angular ordering constraint, a local position constraint, and a neighborhood conserving constraint. Other ancillary geometric information, which includes the initial exterior orientation parameters that are obtained from the platform parameters and a rough DEM, are used to transform the oblique images geometrically and reduce the perspective deformations. Experiment results revealed that the proposed method is superior to the standard SIFT regarding both precision and correct matches using images obtained by the SWDC-5 system.
In recent years, there has been tremendous growth in the field of indoor and outdoor positioning sensors continuously producing huge volumes of trajectory data that has been used in many fields such as location-based services or location intelligence. Trajectory data is massively increased and semantically complicated, which poses a great challenge on spatio-temporal data indexing. This paper proposes a spatio-temporal data indexing method, named HBSTR-tree, which is a hybrid index structure comprising spatio-temporal R-tree, B*-tree and Hash table. To improve the index generation efficiency, rather than directly inserting trajectory points, we group consecutive trajectory points as nodes according to their spatio-temporal semantics and then insert them into spatio-temporal R-tree as leaf nodes. Hash table is used to manage the latest leaf nodes to reduce the frequency of insertion. A new spatio-temporal interval criterion and a new node-choosing sub-algorithm are also proposed to optimize spatio-temporal R-tree structures. In addition, a B*-tree sub-index of leaf nodes is built to query the trajectories of targeted objects efficiently. Furthermore, a database storage scheme based on a NoSQL-type DBMS is also proposed for the purpose of cloud storage. Experimental results prove that HBSTR-tree outperforms TB*-tree in some aspects such as generation efficiency, query performance and query type.
Our study proposes a new local model to accurately control an avatar using six inertial sensors in real-time. Creating such a system to assist interactive control of a full-body avatar is challenging because control signals from our performance interfaces are usually inadequate to completely determine the whole body movement of human actors. We use a pre-captured motion database to construct a group of local regression models, which are used along with the control signals to synthesize whole body human movement. By synthesizing a variety of human movements based on actors’ control in real-time, this study verifies the effectiveness of the proposed system. Compared with the previous models, our proposed model can synthesize more accurate results. Our system is suitable for common use because it is much cheaper than commercial motion capture systems.
三维GIS 是当今乃至未来GIS 技术的主要标志性内容之一，它突破了空间信息在二维地图平面中单调表现 的束缚，为各行各业以及人们的日常生活提供了更有效的辅助决策支持。本文重点介绍了三维GIS 的数据模型、 数据库管理和可视化分析等关键技术及其研究进展，并以武汉市为例展示了三维GIS 对城市立体空间的整体表 达，为大城市、全市域的三维数字城市建设奠定了基础，最后探讨了在智慧城市建设与城市安全中三维GIS将发挥 日益重要的时空信息承载引擎与空间智能技术支撑作用。
Abstract Virtual Geographic Environments (VGEs) are proposed as a new generation of geographic analysis tool to contribute to human understanding of the geographic world and assist in solving geographic problems at a deeper level. The development of VGEs is focused on meeting the three scientific requirements of Geographic Information Science (GIScience) — multi-dimensional visualization, dynamic phenomenon simulation, and public participation. To provide a clearer image that improves user understanding of VGEs and to contribute to future scientific development, this article reviews several aspects of VGEs. First, the evolutionary process from maps to previous GISystems and then to VGEs is illustrated, with a particular focus on the reasons VGEs were created. Then, extended from the conceptual framework and the components of a complete VGE, three use cases are identified that together encompass the current state of VGEs at different application levels: 1) a tool for geo-object-based multi-dimensional spatial analysis and multi-channel interaction, 2) a platform for geo-process-based simulation of dynamic geographic phenomena, and 3) a workspace for multi-participant-based collaborative geographic experiments. Based on the above analysis, the differences between VGEs and other similar platforms are discussed to draw their clear boundaries. Finally, a short summary of the limitations of current VGEs is given, and future directions are proposed to facilitate ongoing progress toward forming a comprehensive version of VGEs.
The Chinese Government and citizens face enormous challenges of disaster management as widespread devastation, economic damages, and loss of human lives caused by increasing natural disasters. Disaster management requires a complicated iterative process that includes disaster monitoring, early detection, forecasting, loss assessment, and efficient analysis of disaster reduction. Each task typically involves the use of technologists and multiple geospatial information resources, including sensors, data sources, models, geo-tools, software packages, and computing resources. However, most existing disaster management systems operate in a typical passive data-centric mode, where resources cannot be fully utilized. This impediment is partially being addressed by the increasingly complex application requirements and the growing availability of diverse resources. In this paper, we summarize and analyze the practical problems experienced by the National Disaster Reduction Application System of China. To address the issues of data-centric, centralized, isolated solutions, we propose a novel Focusing Service Mechanism, which is capable of scheduling and allocating for optimum utilization of multiple resources, to dynamically generate collaborative and on-demand disaster information services. We also demonstrate the design and implementation of the Integrated Disaster Information Service System (IDISS). Through the service strategies of Virtualizing, Wrapping, and Integrating, disaster-related resources are constructed into services in the IDISS. These services are dynamically aggregated into focusing service chains, for diverse disaster management tasks. Actual applications illustrate that the proposed service system can significantly improve the capability of disaster management in China.
A complex 3D city model contains detailed descriptions of both its appearance and its internal structure, including architectural components. Because of the topological complexity and the large volumes of data in such models, profiling is an effective method to present the internal structure, the distributed characteristics, and the hierarchical relationships of the model to provide intuitive visual information to the viewer and to reveal the relationships between the elements of the model and the whole. However, with commonly used boundary descriptions, it is difficult to comprehensively preserve the consistency of three-dimensional profiling using existing algorithms based on geometric constraints. This paper proposes a novel semantics-constrained profiling approach to ensure the consistency of the geometrical, topological, and semantic relationships when profiling complex 3D city models. The approach transforms the 3D model’s boundary description, defined using the CityGML standard of the Open Geospatial Consortium (OGC), into a set of unified volumetric features described as solids. This approach is characterized by (1) the use of the concepts of semantic relationships, virtual edges, and virtual surfaces; (2) the semantic analysis of 3D models and the extraction of volumetric features as basic geometric analytic units; (3) the completion of structural connectivity and space coverage for each volumetric feature, which is represented as a solid model; and (4) the use of a reliable 3D Boolean operation for efficient and accurate profiling. A typical detailed 3D museum model is used as an example to illustrate the profiling principle, and the experimental results demonstrate the correctness and effectiveness of this approach.
This paper presents a flexible method for zoom lens calibration and modeling using a planar checkerboard. The method includes the following four steps. First, the principal point of the zoom-lens camera is determined by a focus-of-expansion approach. Second, the infl uences of focus changes on the principal distance are modeled by a scale parameter. Third, checkerboard images taken at varying object distances with convergent image geometry are used for camera calibration. Finally, the variations of the calibration parameters with respect to the various zoom and focus settings are modeled using polynomials. Three different types of lens are examined in this study. Experimental analyses show that high precision calibration results can be expected from the developed approach. The relative measurement accuracy (accuracy normalized with object distance) using the calibrated zoom-lens camera model ranges from 1:5 000 to 1:25 000. The developed method is of significance to facilitate the use of zoom-lens camera systems in various applications such as robotic exploration, hazard monitoring, traffic monitoring, and security surveillance.
The difference between real-time CSCW systems and traditional distributed systems is that the former one is supposed to provide a natural, free and fast interface for multi-user interaction. However, the typical multi-user interaction method applied in 3D CAD systems is strict consistency maintenance, such as locking mechanism and floor control, which may generate a stagnant and unnatural interface. This paper proposes a 3D semanticbased Operational transformation (OT) to support less constrained multi-user interaction and to achieve consistency in collaborative CAD editing (co-CAD) systems, and it can be used in many collaborative CAD/CAM industries.
The real-time visualization of 3D GIS at a whole city scale always faces the challenge of dynamic data loading with high-efficiency. Based on the multi-tier distributed 3D GIS framework, this paper presents a multi-level cache approach for dynamic data loading. It aims to establish in 3D GIS spatial database engine (3DGIS-SDE) the unified management mechanism of caches on three levels, including: the client memory cache (CMC) oriented to sharing application, the client file cache (CFC) organized by index, as well as the application server memory cache (ASMC) of structural consistency. With the help of the proposed optimized cache replacement policy, multi-level cache consistency maintenance as well as multithread loading model designed in the paper, the engine is able to adaptively make full use of each-level caches according to their own application properties and achieve effective coordination between them. Finally, a practical 3D GIS database based on Oracle 11g is employed for test. The experimental results prove this approach could satisfy multi-user concurrent applications of 3D visual exploration.
A complex 3D building model contains a detailed description of both its appearance and internal structure with authentic architectural components. Because of its high complexity and huge data volumes, using a less detailed representation for the distant visual application of such a model is preferable. However, most mesh simplification algorithms cannot preserve manmade features of such models, and the existing 3D generalization algorithms are mainly proposed for regular-shaped buildings. More importantly, neither method can consistently express geometry, topological relations, and semantics in multiple discrete Levels of Details (LoDs). This paper presents a novel mathematical morphology-based algorithm that generalizes the complex 3D building model in a unified manner using the following steps: (1) semantic relationships between components, which reflect structural connectivity in the building at a certain LoD, are defined and extracted; (2) semantically connected components are merged and trivial geometric features of the components are eliminated simultaneously, with semantics associated with components then updated according to the merging; and (3) post-process is carried out to further reduce the redundancy of facets. The semantic relationships extracted ensure the proper generalization of topological relations and semantics of building components, and mathematical morphological operations implemented in the algorithm are capable of handling closed two-manifold components of various shapes. Experiments on both complex 3D building models in the classical Chinese style and prismatic 3D city models prove the effectiveness of the proposed method.
Typical characteristics of remote sensing applications are concurrent tasks, such as those found in disaster rapid response. The existing composition approach to geographical information processing service chain, searches for an optimisation solution and is what can be deemed a “selfish” way. This way leads to problems of conflict amongst concurrent tasks and decreases the performance of all service chains. In this study, a non-cooperative game-based mathematical model to analyse the competitive relationships between tasks, is proposed. A best response function is used, to assure each task maintains utility optimisation by considering composition strategies of other tasks and quantifying conflicts between tasks. Based on this, an iterative algorithm that converges to Nash equilibrium is presented, the aim being to provide good convergence and maximise the utilisation of all tasks under concurrent task conditions. Theoretical analyses and experiments showed that the newly proposed method, when compared to existing service composition methods, has better practical utility in all tasks.
Vehicle-borne laser-scanned point clouds have become increasingly important 3D data sources in fields such as digital city modeling and emergency response management. Aiming at reducing the technical bottlenecks of management and visualization of very large point cloud data sets, this paper proposes a new spatial organization method called 3DOR-Tree, which integrates Octree and 3D R-Tree data structures. This method utilizes Octree index rapid convergence to generate R-Tree leaf nodes, which are inserted directly into the R-Tree, thus avoiding time-consuming point-by-point insertion operations. Furthermore, this paper extends the R-Tree structure to support LOD (level of detail) models. Based on the extended structure, a practical data management method is presented. Finally, an adaptive control method for LODS of point clouds is illustrated. Typical experimental results show that our method possesses quasi-real-time index construction speed, a good storage utilization rate, and efficient visualization performance.
This paper presents a triangulation-based hierarchical image matching method for wide-baseline images. The method includes the following three steps: (a) image orientation by incorporating the SIFT algorithm with the RANSAC approach, (b) feature matching based on the self-adaptive triangle constraint, which includes point-to-point matching and subsequent point-to-area matching, and (c) triangulation constrained dense matching based on the previous matched results. Two new constraints, the triangulation-based disparity constraint and triangulation-based gradient orientation constraint, are developed to alleviate the matching ambiguity for wide-baseline images. A triangulation based affine-adaptive cross-correlation is developed to help find correct matches even in the image regions with large perspective distortions. Experiments using Mars ground wide-baseline images and terrestrial wide-baseline images revealed that the proposed method is capable of generating reliable and dense matching results for terrain mapping and surface reconstruction from the wide-baseline images.
This paper presents an innovative image matching method for reliable and dense image matching on poor textural images, which is the integrated point and edge matching based on the self-adaptive edge-constrained triangulations. Firstly, several seed points and seed edges are obtained on the stereo images, and they are used to construct a pair of initial edge-constrained triangulations on the images. Then, points and edges are matched based on the triangle constraint and other constraints. The newly matched points and edges are inserted into the triangulations and the constrained triangulations are updated dynamically along with the matching propagation. The final results will be the final edge-constrained triangulations generated from the successfully matched points and edges. Experiments using typical space-borne, airborne, and terrestrial images with poor textures revealed that the integrated point and edge matching method based on self-adaptive triangulations is able to produce dense and reliable matching results. Moreover, from the final matched points and edges, 3D points and edges preserving the physical boundaries of objects can be further derived based on photogrammetric techniques, which is ideal for further object modeling applications.
Reliable image matching is an essential and difficult task in digital photogrammetry and computer vision. Possible problems from geometric distortions, illumination changes, scale changes and difficult texture conditions will result in matching ambiguity, especially for close-range image matching. This paper presents a multiple close-range image matching method for surface reconstruction based on a self-adaptive triangle constraint. This method features two aspects. First, the triangles constructed from the previously matched interest points provide strong geometric constraints for the subsequent point matching combined with gradient orientation and disparity constraints. The dynamic update of the triangulation adapts automatically to the changes of image textures. Secondly, a consistency check in object space is performed to remove possible mismatches. Using three sets of actual triple overlapped close-range images for the experiment, the results revealed that the proposed method provides improved matching reliability.
The paper presents an automatic method for the reconstruction of building models from video image sequences. These videos may be recorded using a hand-held camera or a camera mounted on a moving car. Such terrestrial video sequences are economic and flexible. Presenting buildings as geometric models–rather than for instance a representation from a simple meshing of 3D points–enables one to perform a wide range of analyses. However, sparse 3D points and 3D edges do not contain topological relations. Therefore, integrating building structure knowledge into the reconstruction steps plays an important role in our method. First, some rules are applied to reasonably group the extracted features. Then, a suitable outline and normal direction are specified for each surface patch. Based on these surface patches, a hybrid model- and data-driven method is used to recover a building model from both the extracted surface patches and hypothesized parts. Using the building structure knowledge leads to a simple and fast reconstruction method, and also enables one to obtain the main structures of buildings. The results show that this method correctly sets up topological relationships between generated surface patches and also obtains reasonable structure models in occluded areas. Therefore, the reconstructed models satisfy requirements for both visualization and analysis.
Aiming at the fundamental issue of optimal design of discrete levels of detail (LOD) for the visualization of complicated 3D building façades, this paper presents a new quantitative analytical method of perceptible 3D details based on perceptual metric. First, the perceptual metric is defined as the quantitative indicator of the visual perceptibility of façade details at a given viewing distance. Then, according to the human vision system, an algorithm employing 2D discrete wavelet transform and contrast sensitivity function is developed to extract the value of perceptual metric from the rendered image of the façade. Finally, a perceptual metric function is defined, based on the perceptual metric values extracted at equal interval viewing distances. The minimum detail redundancy model is then proposed for the optimal design of discrete LODs. This method provides a quantitative instruction for generating discrete LODs. The experimental results prove the effectiveness and great potential of this method.
Aiming at the increasing critical issues of existing 2D plans and map‐based methodology for integrated management of advanced buildings and related dynamic property rights in complicated 3D built environments, a novel semantics‐based 3D dynamic house property model with hierarchical levels of detail is proposed in this paper, based on comprehensive analysis of 3D house property objects and various application requirements. This model is characterized by: (1) 3D geometric semantics: a 3D geometry hierarchy of exterior and interior of buildings is defined; (2) thematic semantics, comprehensive house property object and related property right relationships are illustrated; (3) temporal semantics, dynamic representation of house property driven by both geometric events and property right events is involved. This model facilitates comprehensive data mining to analyze spatial relationships and dynamic change of property rights in real 3D built environments and can also support the sale and lease of real estate, facility management, house planning and so on.
The extraction of object features from massive unstructured point clouds with different local densities, especially in the presence of random noisy points, is not a trivial task even if that feature is a planar surface. Segmentation is the most important step in the feature extraction process. In practice, most segmentation approaches use geometrical information to segment the 3D point cloud. The features generally include the position of each point (X, Y and Z), locally estimated surface normals and residuals of best fitting surfaces; however, these features could be affected by noisy points and in consequence directly affect the segmentation results. Therefore, massive unstructured and noisy point clouds also lead to bad segmentation (over-segmentation, under-segmentation or no segmentation). While the RANSAC (random sample consensus) algorithm is effective in the presence of noise and outliers, it has two significant disadvantages, namely, its efficiency and the fact that the plane detected by RANSAC may not necessarily belong to the same object surface; that is, spurious surfaces may appear, especially in the case of parallel-gradual planar surfaces such as stairs. The innovative idea proposed in this paper is a modification for the RANSAC algorithm called Seq-NV-RANSAC. This algorithm checks the normal vector (NV) between the existing point clouds and the hypothesised RANSAC plane, which is created by three random points, under an intuitive threshold value. After extracting the first plane, this process is repeated sequentially (Seq) and automatically, until no planar surfaces can be extracted from the remaining points under the existing threshold value. This prevents the extraction of spurious surfaces, brings an improvement in quality to the computed attributes and increases the degree of automation of surface extraction. Thus the best fit is achieved for the real existing surfaces
Depth contours on a chart are important for safe navigation. The ambiguity problem can appear when points of equal depth are joined in contouring. Unreasonable solutions may mistake a shallow area for a deep one, which could result in a potential danger for navigation. A solution is presented to solve the ambiguity problem using constrained lines formed by two shallow depths. The constrained lines are used to limit the joining of the points with equal depth. Experimental results demonstrate that the proposed solution can reduce the dangers of producing non-existent deep areas in bathymetric contouring.
The efficient display of flooding in intertidal zones is crucial to coastal applications (e.g., coastal zone management and anti-flood directing systems). This paper proposes a new algorithm to plot flooded intertidal areas. Initially, a digital tide-coordinated shoreline (DTS) is traced on the basis of creating a digital intertidal zone model (DIZM) and an instantaneous water surface model (IWSM). Then unconnected depressions are obtained depending on the type of DTS. At the same time, the algorithm detects unconnected depressions by considering the influences of the changing water level, and creates an index from different water levels to corresponding depressions. Finally, unconnected depressions are effectively handled and flooded areas are plotted correctly. Experimental results demonstrate that the proposed algorithm results in a more accurate and efficient display than with traditional algorithms.
The existing road‐network models based on the 2D link‐node of roadway centrelines have inhibited lane‐oriented network flow analysis and multi‐dimensional inventory management in complicated 3D urban environments. This paper proposes a hierarchical lane‐oriented 3D road‐network model (HL‐3DRNM), with a unified modelling language (UML) diagram. HL‐3DRNM is a non‐planar topological model with the support of a 3D lane ribbon cartographic display, which is characterized by: (1) multiple topological and cartographic representations and various abstraction levels (street, road segment, carriageway and lane); and (2) referenced multi‐dimensional road information (point, line, area and volume) at lane level. HL‐3DRNM provides solid mathematical foundations for a more detailed inventory management, effective network analysis and realistic navigation in the increasingly complicated 3D urban transportation systems.
The sub-pixel location of interest points is one of the most important tasks in refined image-based 3D reconstruction in digital photogrammetry. The interest point detectors based on the Harris principles are generally used for stereoscopic image matching and subsequent 3D reconstruction. However, the locations of the interest points detected in this way can only be obtained to 1 pixel accuracy. The Harris detector has the following characteristics: (1) the Harris interest strength, which denotes the distinctiveness of an interest point, is a grey scale descriptor which computes the gradient at each sample point in a region around the point, and (2) the Harris interest strengths of the pixels in a template window centred on the interest point exhibit an approximately paraboloid distribution. This paper proposes a precise location method to improve the precision of the interest points on the basis of these characteristics of the Harris interest strength. Firstly, a least squares fit of a paraboloid function to the image grey scale surface using the Harris interest strength is designed in a template window and a Gaussian-distance algorithm is employed to determine the weight. Then, the precise coordinates of this interest point are obtained by calculating the extremities of the fitting surface. The location accuracy of this method is studied both from the theoretical and the practical point of view. Experimental analysis is illustrated with synthetic images as well as actual images, which yielded a location accuracy of 0·15 pixels. Furthermore, experimental results also indicate that this method has the desired anti-image-noise and efficiency characteristics.
For the purpose of reliable stereo image matching, this paper discusses a novel propagation strategy of image matching under the dynamic triangle constraint. Firstly, the construction and the dynamic updating method for the corresponding triangulations on the stereo pairs are introduced, which are used as both constraints and carriers during the matching propagation. Then, three propagation strategies: the stochastic propagation, the adjacent propagation based on the topological relationship of triangles, and the self-adaptive propagation, which considers the texture features are proposed. The detailed algorithms of these three propagation strategies are also presented. To compare these strategies, a stereo pair with typic texture features is employed to describe the different propagation manners of these three strategies, and an experimental analysis is illustrated with different aerial stereo pairs. From test results, the following has been found: (1) stochastic propagation gives the worst matching results; (2) self-adaptive propagation performs better than the adjacent propagation by making use of the global “best first” strategy. From these conclusions, the self-adaptive propagation strategy is recommended for reliable stereo image matching under the dynamic triangle constraint.
A three-dimensional (3D) spatial index is required for real time applications of integrated organization and management in virtual geographic environments of above ground, underground, indoor and outdoor objects. Being one of the most promising methods, the R-tree spatial index has been paid increasing attention in 3D geospatial database management. Since the existing R-tree methods are usually limited by their weakness of low efficiency, due to the critical overlap of sibling nodes and the uneven size of nodes, this paper introduces the k-means clustering method and employs the 3D overlap volume, 3D coverage volume and the minimum bounding box shape value of nodes as the integrative grouping criteria. A new spatial cluster grouping algorithm and R-tree insertion algorithm is then proposed. Experimental analysis on comparative performance of spatial indexing shows that by the new method the overlap of R-tree sibling nodes is minimized drastically and a balance in the volumes of the nodes is maintained.
This paper compares several stereo image interest point detectors with respect to their repeatability and information content through experimental analysis. The Harris-Laplace detector gives better results than other detectors in areas of good texture; however, in areas of poor texture, the Harris-Laplace detector may be not the best choice. A featurerelated filtering strategy is designed for the Harris-Laplace detector (as well as the standard Harris detector) to improve the repeatability and information content for imagery with both good and poor texture: (a) the local information entropy is computed to describe the local feature of the image; and (b) the redundant interest points are filtered according to the interest strength and the local information entropy. After the filtering process, the repeatability and information content of the final interest points are improved, and the mismatching then can be reduced. This conclusion is supported by experimental analysis with actual stereo images.
Depression filling and direction assignment over flat areas are critical issues in hydrologic analysis. This paper proposes an efficient approach for the treatment of depressions and flat areas, based on gridded digital elevation models. Being different from the traditional raster neighborhood process which is time consuming, a hybrid method of vector and raster manipulation is designed for depression filling, followed by a neighbor-grouping scan method to assign the flow direction over flat areas. The results from intensive experiments show that there is a linear relationship between time efficiency and data volume, and the extracted hydrologic structures of flat areas are also more reasonable than those proposed by the existing methods.
In order to select proper seed points for triangle constrained image-matching propagation, this letter analyzes the affects of different numbers and different distributions of seed points on the image-matching results. The concept of distribution quality is introduced to quantify the distribution of seed points. An intensive experimental analysis is illustrated using two different stereo aerial images and, based on the experimental results, a seed point selection strategy for triangle constrained image-matching propagation is proposed. An automatic selection method is then introduced that gives good distribution quality for a defined number of seed points.
This study demonstrates the utilization of the well-defined points to improve the reliability and accuracy of image matching. The basic principle is: (a) to triangulate a few well-defined points within the stereo model area to form a coarse triangulation; (b) to detect certain amount of corners within each triangle for further matching; (c) to propagate the matching of corner points from the reference points (i.e., the three triangle vertices) to obtain the best matching for each of these corners; (d) to dynamically update the triangulation by inserting the newly matched corner; and (e) to further detect corners and perform matching for them until a pre-defined criteria (the minimum size of triangle or the largest number of points matched) is reached. Experimental results reveal: (a) the false matching caused by the occlusion and repetitive texture is diminished; (b) the accuracy is improved, i.e., with a reduction of RMSE of check points (located in different types of terrain areas) by 12 percent to 62 percent, and a reduction of the largest error by up to two times; and (c) most building corners and boundary points of main objects could be matched directly and accurately.
This paper examines the differences between CyberCity, three-dimensional (3D) geographic information systems (GIS) and CyberCity GIS (CCGIS). A CyberCity is defined as a virtual representation of a city that enables a user to explore and interact in cyberspace with the vast amount of environmental and cultural information gathered about the city. The technical characteristics of a CyberCity GIS prototype software are reported, including the 3D hierarchical modeling technique, the integrated database structure, and the interactive method of visualization of the 3D data of urban environments. The effective integrated data organization strategy for dynamical loading and progressive rendering, which enables CCGIS to support the development, design and presentation of a large CyberCity, is stressed. A pilot application for municipal planning and land information publications has been implemented. This pilot application proved that the hierarchical 3D modeling method and data model are significant to the 3D GIS; the real-time visualization of a large CyberCity needs elaborate data organization and a dynamic loading strategy.
This paper describes a series of tests that measured the effects of 4 factors (accuracy, density of source data, characteristics of the terrain surface, and modeling approaches) on the accuracy of digital elevation models (DEMs). A large area covered by 2 1:10,000-scale maps was selected for testing. The terrain types ranged from flat to hilly to mountainous. Results and conclusions are provided.
Digital terrain modeling has been a research area for more than 40 years in geo-sciences and has become a rather self-contained subject. Digital Terrain Modeling: Principles and Methodology is the only authored book to provide comprehensive coverage of recent developments in the field. The topics include terrain analysis, sampling strategy, acquisition methodology, surface modeling principles, triangulation algorithms, interpolation techniques, on-line and off-line quality control in data acquisition, DTM accuracy assessment and mathematical models for DTM accuracy prediction, multi-scale representation, data management, contouring, visual analysis (or visualization), the derivation of various types of terrain parameters, and future development and applications
Large-scale 3D models are the cutting edge of computer technology
for understanding and planning our urban environments and
infrastructures. These models have emerged from two modelling
structures — systems for architecture, engineering, and construction
(AEC) and geographic information systems (GIS). The problems and
challenges facing today’s modelers, developed for different
purposes, focus almost exclusively on data integration — the ability
to use data originally developed in one modeling system in the other
and vice versa. This need for data transportability is not new, as
evidenced by several authors in this volume. What is new is the
desire to go beyond various conversion programs into an environment
where data is truly integrated, where the modeling framework is more
universal, and where data standards cut across software programs and
This book captures the excitement of researchers, organizations, and vendors in this quest. The border between data structures used within GIS and AEC continues to diminish. As these two principal forms of modeling continue to merge, as the result of increased interest in large-scale 3D models, the need for data structures capable of supporting both types of modeling efforts, as well as new types of modeling efforts that combine the best features of both simple efforts, is manifest.
When disaster occurs, the response phase is viewed as the most critical in terms of saving lives and protecting property. Exploring the development of increased efficiency in emergency services, this volume covers technological advances that allow wider, faster, and more effective utilization of geospatial information. It discusses advances in positioning, virtual reality, and simulation models leading to improved response times in emergency situations. The book also discusses legislative attempts to promote the broader sharing and accessibility of vital information. The authors cover data collection, data production, data management, and 3D routing, as well as lesser known emerging technologies.
“数字城市”既是目标，也是一个过程。最终要达到什么样的境界目前还说不太清楚。但是可以肯定的说它不是一个单纯的技术系统，而是一个“以人为本”，人机结合的大型综合集成体系。本书在这个问题上的描述有明显的特色和亮点，尽管国内外的研究探索只是刚刚起步，但方向是清晰的，应该引起我们的重视。例如，书中提出的构建分布式的虚拟地理环境，开始强调人与虚拟环境的交互与关系；讨论了地理协同（ Geocollaboration）理论在分布式虚拟地理环境中的应用，这必然会引出认知主体和客体，虚拟与实在（ Reality）等跨计算机、心理学和哲学的多种问题，并将引导“数字城市”研究与开发的深化。
近年来，受到“数字地球”（digital earth）概念的影响，“数字城市”（digital city）在不同的认识层次和学科领域得到了不同的理解，因而具有两层明显不同的含义：广义上被用于描述城市信息化的目标，而狭义上则主要指城市空间信息基础设施。不管如何理解，城市地理信息系统都是其重要的核心内容，并正在积极向动态、多维和网络化方向发展。为了突出虚拟现实技术在城市空间信息交流方面的重要意义，“虚拟城市”（virtual city）也被用于描述通常由三维场景组成的城市地区，用户能够在里面移动和交互。
城市逼真的三维数字表示由于其在城市基础设施管理、无线通讯网络规划、城市开发决策支持、污染分布仿真、土木工程与军事行动支持等众多领域显现出巨大的应用潜力，从而成为普遍关注的热点问题。如何从二维地理信息系统向城市环境三维描述（三维地理信息系统）转变正日益成为城市数据管理的时髦问题。城市的三维逼真描述——三维城市模型不仅具有传统虚拟现实表现的高度真实感，而且具有三维GIS数据库管理与分析应用等特殊功能并能与其他社会经济信息互联。因此，三维城市模型常被作为CyberCity的代名词，有关其数据获取与管理的研究受到了广泛重视。格林（Gruen）等学者将三维城市模型数据库系统称为“CyberCity Spatial Information System”（CyberCity空间信息系统）。针对城市地理环境应用，笔者认为CyberCity Geographic Information System(CyberCity GIS)的提法更为恰当，并将其翻译为数码城市地理信息系统。我们认为，数码城市地理信息系统是“数字城市”空间数据基础设施的重要组成部分，也是“虚拟城市”的核心内容；同时，也将其作为GIS向“虚拟地理环境”（virtual geographic environment）方向发展的一个初步原型。因此，本书以“数码城市地理信息系统——虚拟城市环境之三维城市模型初探”作为书名。
本书的完成还得到了许多人直接或间接的无私贡献。有关数码城市地理信息系统的研究与实践一直得到了武汉大学李德仁院士和龚建雅教授的关心与支持。李德仁院士在百忙中审阅了书稿，提出了宝贵的建议并给予了鼓励。解放军信息工程大学高俊院士不顾繁忙的学术活动亲自审阅全书并欣然作序，使本书增色许多，令作者深受鼓舞。要感谢测绘遥感信息工程国家重点实验室（武汉大学）和地球信息科学联合实验室（香港中文大学）有关的教师、博士研究生和硕士研究生们给予的极大支持。在几年前首次策划本书内容时，香港理工大学的李志林教授提出了许多宝贵的意见和建议，它们已经体现在今天的书稿当中。作者要感谢眭海刚博士，吴波、赵杰、黄铎、张霞、胡海棠、王静文、韩李涛、李逢春、龚俊、张叶廷、钟正等博士研究生，高玉荣和周艳等硕士研究生的辛勤付出。同时，作者还要感谢香港裘搓基金会赞助朱庆在香港中文大学地球信息科学联合实验室的访问和学术交流，使其有机会与龚建华研究员、辛晓红博士、沈大勇博士、孔云峰博士、杨育彬博士、李响、赵一斌、施晶晶和王纲胜等博士研究生进行深入讨论，并有颇多收益。本书得到了国家973项目“虚拟现实的基础理论、算法及其实现”（2002CB312101）、 国家863项目“ 虚拟地理环境的研究与开发 ”（ 2001AA135130）和国家自然科学基金项目“多种类型大型空间数据库集成方法”（40001017）的资助。
本书是在中国科学院和中国工程院院士、测绘遥感信息工程国家重点实验室主任李德仁教授的热情鼓励和指导下完成的。承蒙他在百忙中审阅全书并作序，特此表示深深的敬意和感谢。感谢测绘遥感信息工程国家重点实验室常务副主任、首批“长江学者奖励计划”特聘教授龚健雅博士审阅全书并提出宝贵意见。 感谢研究生周艳、高玉荣和王丽圆同学在资料整理过程中付出的大量艰辛劳动。 我们也非常感谢武汉大学出版社把本书作为她的“数字地球丛书”之一跟读者见面。
Prof. Zhu has a long teaching and researching experiences in GIS, especially on the Digital Elevation Model, 3D GIS and Virtual Geographic Environments.
graduate student, 36 courses, Southwest Jiaotong University
graduate student，Southwest Jiaotong University
graduate student, 36 courses, Wuhan University
graduate student, 36 courses, Wuhan University
graduate student, 36 courses, Wuhan University
graduate student, 36 courses, Wuhan University
Ph.D. student, 36 courses, Wuhan University
overseas student，Southwest Jiaotong University
Southwest Jiaotong University
Prof. Qing Zhu
Faculty of Geosciences and Environmental Engineering
Southwest Jiaotong University
999 Xi'an Road, Gaoxin Xi District, Chengdu, China
My office in Southwest Jiaotong University is at the top floor of the 4th Block in the Xipu campus.
I am at my office every day from 8:00 until 16:00 pm, but you may consider a call to fix an appointment.
Some of my supervised students are still in LIESMARS of Wuhan University.
You can also meet me there occasionally!