On three-dimensional visualization of geospatial information: graphics based or imagery based?

Transcription

1 Annals of GIS ISSN: (Print) (Online) Journal homepage: On three-dimensional visualization of geospatial information: graphics based or imagery based? Li Deren, Wang Mi, Hu Qingwu & Hu Fen To cite this article: Li Deren, Wang Mi, Hu Qingwu & Hu Fen (2009) On three-dimensional visualization of geospatial information: graphics based or imagery based?, Annals of GIS, 15:2, 75-84, DOI: / To link to this article: Published online: 14 Dec Submit your article to this journal Article views: 589 View related articles Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at

2 Annals of GIS Vol. 15, No. 2, December 2009, On three-dimensional visualization of geospatial information: graphics based or imagery based? Li Deren, Wang Mi*, Hu Qingwu and Hu Fen State Key Laboratory of Information Engineering in Surveying Mapping and Remote Sensing, Wuhan, China (Received 15 April 2009; final version received 25 May 2009) The three-dimensional (3D) visualization of geospatial information constitutes a fundamental property of the geo-information services nowadays, along with the requirements of popularity, openness and capabilities of target measuring and knowledge mining. Accordingly, in this article, the two major technical routines now applied to 3D visualization of geospatial information, that is the graphics-based approaches and the imagery-based approaches, are both described and discussed. After a comparative analysis of both advantages and disadvantages of the two manifestation modes, an optimized integrative strategy for 3D visualization of geospatial information is proposed finally. Keywords: geospatial information; 3D visualization; graphics based; imagery based; digital measurable images; measurable virtual reality 1. Introduction To a large extent, the geospatial information composes the most fundamental section of the real world, which is ceaselessly exploited, recognized and renovated by human beings. It takes a very important function in social life and productive practices of mankind with widespread and penetrating influence. As we all know, the nature we live in is a three-dimensional (3D) space, in which people observe the majority of the entities stereoscopically. Intoxicated by the versatility and beauty of natural sceneries, people never cease in pursuing the best 3D representation style to vividly and stereoscopically recover the geographic landscapes. In the information era, the most ideal approach is visualizing such 3D space in the computer environment by which capabilities of virtual landscape roaming, target querying and analyzing are supported. Throughout the developing history of human society, the manifestation and propagation patterns of geographic information have undergone a series of innovations ever since the beginning of time, that is from languages, characters and maps to geographic information science (GIS) and virtual geographic environments (Gong and Lin 1999). Now it has already become the worldwide focus to develop various techniques for 3D visualization of geospatial information. We are living in a highly informationized period, the new advanced technologies developing fast and the social requirements constantly changing. Under the circumstances, a revolution that transforms the conventional map-based productive mode to the integrative geospatial information-based service mode is now sweeping the area of surveying and mapping, and 3D visualization of geospatial information has become a prominent characteristic of geo-information service, along with the requirements of popularity, openness and capabilities of target measuring and knowledge mining (Li and Shao 2008a). It is not only one of the key issues affecting the development of 3D GIS (Xiao et al. 2001, Zhu 2004) but also the basis that guarantees the experiencing capability of geospatial information-based services (Li and Hu 2007, Li and Shao 2008b), such as Google Earth, Virtual Earth, Image City and so on. Actually, the 3D manifestation form of geospatial information has many advantages that the traditional 2D form can hardly be compared with. As we know, the traditional GIS visualization primarily adopts the 2D graphics or single image-based methods, and this kind of technical routine has a wide and long-term market in application fields of remote spatial data visualization, location-based service as well as intelligent transportation navigation. The main reason is that the data volume involved in a 2D visualization environment is very small, and the relevant theories and techniques are highly sophisticated and mostly reliable. However, the traditional electronic maps are just a 2D projection of the real world according to certain geo-positioning references. In such a manifestation approach, the spatial information is transformed from 3D to 2D for visualization by means of data simplification and abstraction. Most often only the location of the feature elements are cared about, while a lot of precious details embodying the topographic and terrain attributes such as texture, height and shape are all omitted and lost. Imaginably, such manifestation certainly has heavy *Corresponding author. wangmi@lmars.whu.edu.cn ISSN print/issn online 2009 Taylor & Francis DOI: /

3 76 L. Deren et al. disparity with the real geographic environment and leads great inconvenience to practical utilization of geospatial data, especially incompatible with the requirements of the geo-information service on the web currently (Li and Shao 2008a, 2008b). In addition, as an important surveying and mapping product, digital orthoimage model is also another 2D representation pattern of geographic data. It is characterized by well keeping the texture information of terrain and topographic entities, but the disadvantage of lacking the elevation information about terrain surface and the attributes of ground objects is also apparent. Therefore, it can be perceived that the traditional manifestation approaches are almost based on 2D projection of 3D landscapes, where most of the depth information originally existing is lost. In this situation, people identify and feel the hierarchy of scenery depth by empirical knowledge such as shadow, occlusion or symbolic understanding, andthisisobviouslyunreal. Compared with 2D representation, it will be more straightforward and eidetic to use the reconstructed 3D models to manifest the real-world entities through computers, because the leading approach to 3D manifestation is no longer abstract symbolization and generalization (e.g., 2D electronic map) but simulation (e.g., 3D reconstruction) of reality instead. Our surrounding is a 3D space and the recognition space of our mankind is also in multidimensional and multi-angular style, so the ideal state of geospatial information visualization goes to objective reflectance of the real world. With the emergence of virtual reality (VR) technique and so on, such an ideal situation is gradually closer to the reality, and the combination of VR and GIS further enhances the human interactivity in geoinformation services. 3D geo-information visualization is an effective routine that handles the contradiction between recognition space of mankind and method space where we used tools to solve problems and can provide us with more choices to inspect the reality. Development in some related disciplines such as computer vision and computer graphics has brought in many new technologies for interactive 3D visualization, which improves the geospatial data analyzing capacities and extends the manifestations of geospatial data so that a dynamic, vivid, multi-angular and multi-level feature depiction of ground space is available. After all, 3D visualization takes an irreplaceable position in exploiting the various spatial phenomena and speeding the information handling process. It now becomes the basis and key technique in many GIS applications such as intelligent transportation navigation, location-based service, virtual architecture environment, surveying and mapping, urban planning, network and multi-media, digital culture heritage, virtual battlefield construction, and virtual tour information query. In the future, with the further development of the next generation of Internet and 3G mobile communication techniques, 3D visualization of geo-information will penetrate into more areas of our social life. 2. The approaches to three-dimensional geoinformation visualization 2.1. The graphics-based 3D visualization of geoinformation Currently, a common category of 3D visualization methods are based on terrain and object models graphically constructed, including DEM, DSM and 3D models of ground features (Yang et al. 2000, Zhu et al. 2002, Du et al. 2003, Suresh et al. 2005, Jin and Gao 2006, Kolbe et al. 2008, Zhu et al. 2009). Firstly, establish the 3D geometric models in the scenery by the computer, then perform the coloring, blacking, illuminating, texturemapping and projecting processes, and the virtual scenery are finally generated. Generally speaking, we categorize methods in this technical routine as the graphics-based 3D visualization of geo-information. There are diverse manifestations of geographic and natural phenomena, such as continuousness in space, concreteness in distribution and complication in attributions represented by multi-scale, multi-angular observations. Therefore, although we can take a personal experience from graphics-based 3D visualization and have more choice to facilitate our policy-makings, a great number of challenges and problems also arise consequently (Suresh et al. 2005, Jin and Gao 2006, Zhu et al. 2009). For example, the high workload for 3D feature collection, the demand of efficient 3D modeling, the management of a large data volume, the representation of intricate spatial relationship of ground features and the real-time displaying and roaming of 3D models with sense of reality. In general, the geospatial data are acquired either in the manner of point or in the manner of area. The former mentions about collecting the 3D coordinates and attributes of the ground surface points by means of geodetic surveying, GPS and other ground surveying techniques; besides, airborne and ground-based Lidar collecting data by point clouds also belongs to this category (Du et al. 2003, Vosselman 2008). Data acquisition in the manner of area generally captures large-scale stereo-imageries in the way of aerial, space, and close-range photogrammetry and then extracts the 3D geometry and texture features of terrain and man-made objects from these stereo-imageries. Now, to acquire geospatial data by multi-sensor integrated system is also an important trend currently (Tao 2005, Li 2006), for example mobile mapping system (MMS), multi-angular oblique aerial camera as well as airborne Lidar. Overall, the geospatial data acquisition techniques now tend to be more rapid, dynamic, automatic and intelligent. Geospatial data acquired from different sources are then used for 3D feature extraction and model reconstruction by specific methods and tools (Tao 2005, Zhu et al. 2009). For example, 3D modeling can be performed based on the web-oriented VRML or by some professional tools like 3DMax and Maya (

4 Annals of GIS 77 Figure 1. Modeling of cyber city based on optical RS images (Shenzhen). Figure 2. Modeling of cyber city based on airborne Lidar scanning data (Nanjing). Besides, registration and erosion of Lidar scanning data and optical images, DEM generation from stereo-imageries or InSAR data, etc., are among the important issues for accurate 3D modeling. Figures 1 and 2 separately illustrate the 3D modeling procedures based on optical images and Lidar point clouds. Of such processes, texture-mapping of 3D models is the most time-consuming with large data volume. At present, the typical features of graphics-based 3D visualization include dynamic data loading, progressive drawing of graphics, levels of detail (LoD) representation and VR manifestation and so on (Yang et al. 2000, Zhu et al. 2002, Suresh et al. 2005, Jin and Gao 2006, Zhu et al. 2009). The highly effective spatial data scheduling mechanism and graphical drawing strategy can provide geospatial information with diverse, interactive and dynamic 3D visualization functionalities. Moreover, the realistic, interactive visualization of the mass 3D GIS also poses particular demands to both hardware and software environment of computers, accordingly some advanced graphic cards and workstations have already emerged for this purpose. For example, in addition to some semi-immersion perspective displaying system, the full-immersion real 3D visualization platforms are gradually used in the 3D GIS systems nowadays The imagery-based 3D visualization of geoinformation With the development in disciplines of digital photogrammetry, computer vision and VR, the imagery-based 3D visualization of geo-information is another technical routine often adopted (Collins 1968, Zhang et al. 2002, Li and Wang 2004, Thomas and Werner 2004, Wang 2004, Li 2007, Li et al. 2009). Different from the graphics-based approaches, it directly builds the artificial stereoscopic vision and stereo-measuring environment from epipolar stereo-models, stereo-orthoimage models or panoramic sequential images; thus it will be more economical. To sum up, the imagery-based 3D visualization of geoinformation has three major representations, that is, measurable virtual reality (MVR), digital measurable images (DMI) and 3D panoramic images.

5 78 L. Deren et al MVR It is the basis of digital photogrammetry to build up manmade stereoscopic models based on the physiological characteristics of human eyes. The aerial images most often hold a certain overlapping rate along and across the flight lines, thus ensuring the involvement of 3D information of ground surfaces (Li and Zheng 1992). Digital orthoimage is a type of information-rich digital product generated by correcting projective distortions (caused by terrain relief and image tilt, etc.) of the original image. Although digital orthoimage has correct planar position and holds abundant image information, it is still insufficient for utilization as the height information of terrain surface and terrain objects is lost. Digital terrain model (DTM) is a common 3D representation of terrain surface, but it lacks textures for interpretation purpose and has no representation of terrain objects. As we know, the epipolar stereo-model generated from a pair of overlapped aerial imageries offers the possibility of 3D measurement and texture information for interpretation. However, it cannot be used as a plan like the case of digital orthoimage and the model size is usually limited to the stereo-pair. Indeed, it is very desirable to have a product that has the advantages of orthoimage (i.e., information rich, possible for 2D measurement), stereo-model (i.e., possible for 3D measurement) as well as DTM (i.e., 3D representation of a large area). It is noticeable that the stereomate introduced by Collins (1968) at the National Research Council of Canada serves part of the purpose. The stereomate is a complementary image to an orthoimage. It is a new image with additional relief displacement. The total amount of relief displacement at each point of the stereomate is exactly the same as the sum of two relief displacements at the same position on both images of the stereo-pair. That is, if this stereomate is used together with the orthoimage, one is still able to reconstruct a 3D surface of the area precisely. Simplicity and efficiency of using the stereo-model are of particular interest and value for many users. The idea was great and this promotes the claim that digital stereo-imagery can be taken as a map product in the future in practical applications. However, restricted by the technological conditions of the time, the device for digital stereo-imagery production is highly complicated; besides, the study of digital stereo-imagery is only concentrated in the scope of just one stereo-image pair instead of the large-scale area (Collins 1968). With the development of digital photogrammetry, the orthoimage now has the seamless mosaic characteristic, and it has already become the truth to construct the seamless orthoimage database of large areas. Under the circumstances, Li Deren and Wang Mi (2004) propose the idea and concept of MVR based on a seamless orthoimage database. The main idea is to generate a digital stereo-orthophoto partner (DSP) from DEM and original image. A geometrically correct 3D landscape model will be obtained by means of the stereoscopic view of DOQ (digital orthophoto quadrangles) and DSP (Li and Wang 2004, Wang 2004). Users not only see the real 3D landscape model (i.e., VR) but also measure the plane coordinates and elevation of interesting features (i.e., measurable). Then, we can artificially produce a so-called DOQ and DSP to all together form the stereo-orthophoto pair, and the measurable seamless stereo-model is developed by a mosaic orthoimage (i.e., mosaics of a whole block of aerial photographs) and a mosaic stereomate, with the lineage (i.e., image coordinates on original photograph and the orientation parameters of the original photograph) of each pixel on both mosaic orthoimage and a mosaic stereomate recorded (Wang 2004). Such a measurable seamless stereo-model not only provides a seamless 3D landscape environment but also offers the rigorous and thus accurate 3D measurement of any object and feature visible in the measurable seamless stereo-model without an explicit orientation procedure. Figure 3 shows a case of MVR based on measurable seamless stereo-model. As it completely does not rely on the delicate modeling of ground features but just directly develops the virtual scenery from the original photogrammetric image data, the MVR-based 3D geo-information manifestation is thus quite different from graphics-based visualization mode. MVR is excellent in conquering the limitation of traditional stereo-mapping system, which only takes each single stereo-model as the basic mapping unit. Overall, MVR truly reappears on the 3D terrain surface and terrain objects at the image-capturing instant, thus identified as a desirable routine for 3D visualization, measurement and analysis of geomatics data DMI DMI (Li 2007, Li and Hu 2007, Li and Shao 2008b, Li 2009) is the common name of absolute oriented airborne, spaceborne and ground-based image stereo-models in uniformly administrated spatial-temporal sequences. It is not only straightforward but also provides users with the capabilities of on-demand stereo-viewing and measuring, relative and absolute orientation of stereo-models as well as mining of attribute data, by some professional devices with related application software, plug-ins and API installed on them. Moreover, DMI with a time dimension included is an abundant source of historical mining data useful to the spatial information multi-grid technology (Shao and Li 2005) and provides the users with self-extensible data for applications of visibility analysis, transportation capacity analysis, commercial sites selection, etc. Moreover, DMI is a new-type digital product conforming to the criterion of Web2.0 (Li 2007, Li and Hu 2007), which is able to embody the breakthrough that changes the rules-oriented spatial data measurement mode for professional operators to the ondemand spatial data viewing, measuring and analysis mode for widespread users.

6 Annals of GIS 79 Figure 3. Left side: valid polygon of mosaicked orthoimages; right side: MVR built up by measurable seamless stereo-model. DMI captured by the POS (position and orientation system)-aided photogrammetry system (the system integrates geodetic quality GPS, INS and multiple digital stereo-cameras that are mounted on a land vehicle) that works without ground control have uniform geo-reference and can be easily integrated to the existing data resource and information system as well as the internet by software with no need of extra processes, thus providing direct, straightforward 3D imagery-based visualized services. Figure 4a gives an instance showing the rapid 3D visualization project of Qinghai Tibet Railway based on DMI. Here the image data collection work is finished within one week by a MMS. The purpose of the project is to provide a 3D visualized servicing environment for completion acceptance of the engineering, emergency policy-making, operations and asset management, etc. Figure 4b shows an instance of Image City, which provides on-demand city guidance service to the users based on DMI. In this application, three sets of MMS work in synchronism to accomplish the 3D geospatial data collection task of a big city within a month. DMI proves to be a rapid, convenient, accurate and economic tool for geomatics data collecting and updating. With respect to the 3D visualization forms of geoinformation, it is said that a picture is beyond thousands of words. The visual, measurable and minable DMI can vividly reflect the physical situations of the earth s surface, which is unable to be transmitted by traditional maps, and supplies us an earth hologram with GIS knowledge relevant with the society, economy and humanities contained. In addition, technological developments in modern information, computer network, database and VR stimulate the integrative combination, merging, management and sharing of mass DMI data and conventional 4D (DOQ, DEM, DRG and DLG) products, thus accelerating the formation process of the information-rich, up-to-date 5D national fundamental geospatial database (Li 2007). It is valuable for the visualization-based geo-information service nowadays. Besides, the DMI-based 3D visualization is advantageous in high displaying speed when compared with the 3D graphics-based visualization, thus drastically cutting the economical cost and improving the updating efficiency of 3D visualization of geospatial data. Moreover, DMI can also be seamlessly combined with the graphics-based 3D models so as to implement an effective integration of virtual models and real images. In this way, superiorities of the two manifestation modes can be exerted to the greatest extent. Figure 5 gives an instance combining DMI and virtual 3D models. In this figure, the cars, flower bowls and chair are all 3D models constructed by 3DMax, which are backprojected to the DMI environment in the virtual scenery. It indicates indirectly that the DMI-based visualization is in 3D style and is very convenient for the analysis of 3Dvisualized virtual scenery D panoramic image With the development of digital graphics technology, the imagery-based VR came into being and developed rapidly, with the breakthrough brought by the dissemination of 3D panoramic images (Thomas and Werner 2004). Actually, it is of much realistic meaning and academic value to simulate the capturing and recording process of 3D panoramic images through computers. 3D panoramic images simulated in this way are almost similar to those provided by optical sensors. Now there is an increasingly widespread concern about the application value of 3D panoramic images, in

7 80 L. Deren et al. (a) (b) Figure 4. (a) 3D visualization of Qinghai Tibet Railway based on DMI. (b) 3D visualization of Image City based on DMI. regard to the strong realistic feeling it brings as well as the convenience in panoramic images production. Apart from the direct imaging/photography and the computer-based simulation, the digital 3D panorama is another source of 3D panoramic images. The essence of digital 3D panoramas is to transform planar photos, planar images or computer graphics to the 360 angular panoramic mosaic image that is quite popular for VR browsing. That is, a series of adjacent 2D planar images with different perspectives are used to simulate the virtual 3D space to the viewers. The viewers realize the zooming in, zooming out of the virtual scenery and change the viewing angles at will, based on the supplied manipulation functions, to achieve the good simulation effect of the realistic environment. According to different browsing modes, there are cylindrical panorama and spherical panorama, etc., which are all able to accomplish any angular observation of 3D virtual scenery. Figures 6a and b are respectively instances of cylindrical panorama and spherical panorama Comparison between the two types of manifestation approaches Subsequently, the imagery-based and the graphics-based 3D visualization modes are comparatively analyzed, from the perspectives of theoretical basis, data source, approaches of data collection, capability in stereomeasuring and spatial analysis and so forth. Actually, such two kinds of manifestation types have both advantages and disadvantages, respectively, according to their characteristics in practical applications. On the one hand, the graphics-based visualization of geo-information is featured by supplying users with multidimensional, multi-angular measuring functions and 3D

8 Annals of GIS 81 Figure 5. An instance of combination between real DMI and 3D virtual models. (a) (b) Figure 6. (a) An instance of cylindrical panorama. (b) An instance of spherical panorama. analysis capacity and has a wide application domain covering Digital City, virtual geographic environments and so on. The graphics-based visualization is excellent and capable of exploring both external and internal structures of the interested 3D models, compared with the imagery-based visualization that provides only the outside structures of the objects to the users. For example, when 3D building models covering both external and internal structures

9 82 L. Deren et al. should be established for emergency response and spatial analysis, the graphics-based realization method will be preferable. Besides, the graphics-based visualization can flexibly vary observation angles of 3D models, but in MVR it is often impossible to view the wall surfaces and the street facades of the buildings, and for DMI it is hard to look at the roof and behind buildings on the road sides. However, some technical issues also exist for graphics-based visualization. Firstly, as all the manifested terrain and topographic models need to be collected and reconstructed in advance, the workload of data collection or feature extraction is heavy; secondly, the realization of fully automatic 3D modeling of spatial entities still has a long way to go, that is, the humaninteractive operations now take the leading place; thirdly, it shows a higher demand in computer hardware aspect because of the huge data volume; fourthly, there is still space to be improved in consideration to the efficient 3D graphics roaming in/out of large complicated areas, although the corresponding technologies have gained speedy development in the past several decades. So far, it is still hard to keep both qualified vision effect and high refreshing frequency in practice, in terms of the mass data volume and complicated terrain conditions and objects. Now, a primary solution is to release such burden from the perspective of 3D modeling, for example establishment of multi-resolution 3D models and LoD algorithms. On the other hand, as we mentioned before, it will be more economical and practical to directly construct the artificial stereoscopic vision from stereo-imageries or 3D panoramic images. Using stereoscopic viewing devices, the terrain surface and topographic conditions at the exposure moment can reappear from the established image stereomodels that eliminate the vertical-parallaxes of original stereo-imageries, with no need of prior 3D feature collection and modeling work. The imagery-based 3D visualization is also noticeable to effectively support the measurement-ondemand geo-information services currently and thus compensating the defection that in the graphics-based visual environment the users can only browse and measure the 3D models already existing in the virtual scenery. In addition to image stereo-models, the 3D panoramic images, which simulate the realistic scenery by perspective processing of images, also bring strong immersive feelings to the viewers. The 3D panoramic images are low cost, time saving, easy to produce and convenient to network transmission. However, in terms of multi-angular scenery observation and geospatial analysis, the imagery-based 3D visualization mode is not as excellent as the graphics-based manifestation. Table 1 gives an overview comparison of the two kinds of 3D visualization approaches. 3. Conclusions Overall, the two modes discussed in this article for 3D visualization of geo-information both have their own advantages and disadvantages. To reach the optimal application quality of 3D geo-information visualization, it is a considerable choice to combine them together in practice. Here, after comparatively analyzing the pros and cons of the two kinds of manifestations, the authors would like to give out an integrative visualization strategy, which is depicted as below. (1) Establish the graphics-based 3D wire-frame models and the simplified textures, which are used for spatial analysis in 3D GIS. (2) Construct the imagery-based 3D scenery models applied to visualized analysis and stereo-measuring. (3) Establish graphics-based 3D fine models in areas and landmarks of interest and execute the fine texture-mapping for 3D realistic visualization and spatial analysis. (4) It is recommended to back-project the new ground objects designed in CAD system to the 3D Table 1. Comparing the advantages and disadvantages of the two manifestations in 3D visualization. Properties in comparison Graphics-based methods Imagery-based methods Theoretical basis Computer graphics and images Digital photogrammetry, artificial stereo-vision Data sources Vector models and texture images Digital stereo-orthophoto partner, digital orthophoto quadrangles, close-range image sequences Geometric modeling Required Not required Texturing modeling Required Not required Computation amount Large Small, in fact very little Feature collection and Heavy workload, high cost and long time cycle Actually not required, cost saving and short time cycle modelling Measurability Measured on the reconstructed 3D models, both inside and outside of the 3D models Measured on all the objects in 3D imageries, but only get outside structure of the object models The visualization scope Only display objects that are collected and Display the 3D landscapes totally modeled in prior With multi-angular Yes Not totally, just depending on the imaging/photographic observation supported Geospatial analysis capability Superior viewing angle Weak

10 Annals of GIS 83 Figure 7. An instance of the integrative 3D visualization mode (Digital City of Qianjiang). imagery-based virtual scenery, which is quite beneficial to the rapid planning, and visioneffectiveness analysis of architectures, etc. Obviously, the imagery-based 3D visualization supplies a full macro-environment for rapid landscape viewing and on-demand measurement, to a large extent releasing the workload input in graphics-based visualization aspect; the graphics-based 3D fine models in turn are good supplements to stereoscopic vision purely built up by 3D imageries, which can facilitate geospatial analysis and policy-making and so on. To realize such an integrated 3D visualization approach, some key problems need to be handled well, such as how to achieve the unified administration, efficient organization, rapid dispatch and synchronized display of multi-source data in the integrative 3D visualization system, how to design an optimized environment for 3D geospatial data visualization in aspects of algorithm optimization and hardware configuration and so forth. Figure 7 shows the Digital City of Qianjiang represented by the integrative 3D visualization approach. Based on such a unified manifestation, the aim of accomplishing the 3D GIS visualization with sound quality and high speed can be reached. Acknowledgments This paper was supported by the National Key Technology R&D Program (2009AA12Z120) and the National Natural Science Foundation of China under Grant References Collins, S.H., Stereoscopic orthophoto maps. The Canadian Surveyor, 22 (1), Du, J., Chen, X.Y., and Fumio, Y., Generation of 3D virtual geographic environment based on laser scanning technique. Geo-Spatial Information Science, 6 (3), Gong, J.H. and Lin, H., Virtual geographical environments: concept, design, and applications. Proceedings of the international symposium on digital earth, (ISDE), November 29 December 2, Beijing, China, Jin, H.L. and Gao, J.X., The research development of 3D terrain visual technique. Science of Surveying and Mapping, 31 (6), Kolbe, T.H., Gröger, G., and Plümer, L., CityGML 3D city models and their potential for emergency response. In: S. Zlatanova and J. Li, eds. Geospatial information technology for emergency response. London: Taylor & Francis. Li, D.R., Mobile mapping technology and its applications. Geospatial Information, 4 (4), 1 5. Li, D.R., On concept and application of digital measurable images from 4D production to 5D production. Science of Surveying and Mapping, 32 (4), 5 7. Li, D.R. and Hu, Q.W., Digital measurable image based geospatial information service. Geomatics and Information Science of Wuhan University, 32 (5), Li, D.R. and Shao, Z.F., 2008a. The intrinsic property of geoinformatics is service. Bulletin of Surveying and Mapping, 5, 1 4. Li, D.R. and Shao, Z.F., 2008b. Image city Wuhan. Geospatial Information, 6 (3), 1 5. Li, D.R. and Wang, M., Method for generating measurable seamless orthoimage stereo model with high accuracy and its application based on aerial images. Railway Survey, 1, 1 6.

11 84 L. Deren et al. Li, D.R. and Zheng, Z.B., Analytic photogrammetry. Beijing: Surveying and Mapping Press. Li, D.R., et al., Digital earth with digital measurable images. In: Virtual geographic environment, Ed. Hui Lin and Michael Batty. Chapter 17. Beijing: Science Press. Shao, Z.F. and Li, D.R., Spatial information multi-grid for data mining. Proceedings of Advanced Data Mining and Applications, ADMA 2005, 3584, Suresh, L., et al., D geospatial visualization of the UCSC campus. Proceedings of ASPRS Annual Conference on Geospatial Goes Global: From your Neighborhood to the Whole Planet, 7 11 March 2005, Baltimore, Maryland. Tao, C.V., D data acquisition and object reconstruction for AEC/CAD. In: Large-scale 3D data integration: challenges and opportunities, Ed. Sisi Zlatanova and David Prosperi. London: CRC Press. Thomas, L. and Werner, T., D object reconstruction from multiple-station panorama imagery. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 34 (5/W16). Vosselman, G., Extraction of 3D building models from airborne laser scanning data. The 3rd ISPRS summer school on Acquisition, processing and representation of threedimensional geospatial information, Nanjing Wang, M., A new approach for generating a measurable seamless stereo model based on mosaic orthoimage and stereomate. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 35 (3), Xiao, L.B., et al., A discussion on basic problems of 3D GIS. Journal of Image and Graphics, 6A (9), Yang, B.S., Li, Q.Q., and Mei, B.Y., Study of the visualization of three-dimension urban model. Acta Geodaetica et Cartographica Sinica, 29 (2), Zhang, Z.X., Zheng, S.Y., and Zhang, J.Q., Threedimensional visualization engineering design. Geomatics and Information Science of Wuhan University, 27 (4), Zhu, Q., A survey of three dimensional GIS technologies. Geomatics World, 2 (3), Zhu, Q., et al., CyberCity GIS (CCGIS): integration of DEMs, images and 3D models. Photogrammetric Engineering & Remote Sensing, 68 (4), Zhu, Q., et al., Research and practice in three-dimensional city modeling. Geo-Spatial Information Science, 12(1),18 24.