FHP_GTOPO30: User Interface to Geo-Referenced Data on the Web

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1 FHP_GTOPO30: User Interface to Geo-Referenced Data on the Web Rolf Däßler Fachhochschule Potsdam Pappelallee 8-10 D Potsdam, Germany Günther Neher Fachhochschule Potsdam Pappelallee 8-10 D Potsdam, Germany ABSTRACT This paper describes the prototype system FHP_GTOPO30, a tool for the VRML-based mid-resolution terrain visualization of the entire Earth s surface. FHP_GTOPO30 is an application that allows the web-based access to the entire USGS GTOPO30 dataset. One focus of FHP_GTOPO30 lies in the user interface design, allowing even inexperienced users to precisely select from and navigate accurately through the large GTOPO30 dataset. Another focus lies in the flexible integration of external information resources, both global and local, into a geographical context. The system is designed to meet prototypically the following requirements for an information system with geographical reference, which to our knowledge is new in this combination: (a) User-friendly, purely mouse-based selection of a desired part of the world. (b) Preservation of the global context reference on each level of detail by the principle of 'discrete zooming'. (c) Flexible integration of global information (e.g. vegetation zones) by means of so-called 'information textures'. (d) Flexible integration of local information (e.g. city information). The FHP_GTOPO30 application is publicly available under the URL: Keywords Graphical User Interface Design, VRML, Geographic Visualization, GTOPO30, World Wide Web, Navigation, Map Generator 1. INTRODUCTION In the past years access to geo-referenced information has become increasingly important and publicly available through real-world technical applications like the Global Positioning System (GPS) for navigation and localized information purposes. While less important to GPS applications, topographic data and their visualization as three-dimensional elevation models play an increasingly important role in many commercial and noncommercial disciplines, including environmental sciences, city planning, military as well as education. Initiatives like the Digital Earth project [1] or NASA s Shuttle Radar Topology Mission (SRTM) finished in February 2000 [2] underline the efforts made in this area. Many of these topographic data are publicly available and, as the Internet becomes more and more important as the world-wide communication medium, many efforts are under way in the field of web-based Geographic Visualization. The language of choice for the three-dimensional visualization and distribution of geo-referenced data over the web is VRML/X3D, allowing in a transparent manner to map feature information into a topographic context [3, 4]. The VRML-based Geo-Visualization resources found on the web today mainly fall into three categories: at the low-end there are static, image-textured ElevationGrids covering limited areas, often small parts of larger, publicly available datasets like ETOPO5, which covers the entire Earth at a resolution of 10 km [5] or GTOPO30, which covers the entire Earth at a resolution of 1 km [6]. In the mid-range there are web-based applications that in principle cover the entire Earth and dynamically generate VRML-based elevation models of user-defined areas. To our knowledge David Pape s ETOPO5 Map Generator, based on the ETOPO5 dataset was one of the first tools of this kind [7]. At the high-end are located applications like TerraVision II [8] or the initiative of the GeoVRML Working Group [9]. TerraVision II uses sophisticated LOD techniques to tackle the problem of making available over a small-bandwidth web high resolution datasets. The GeoVRML Working Group tries to provide VRML-based solutions to seamlessly integrate datasets of different sources generated with different geographical standards. With respect to the underlying dataset the FHP_GTOPO30 system is located in the mid-range; It covers the entire USGS GTOPO30 dataset, which consists of about 2 gigabytes of raw data. The main focus of FHP_GTOPO30 neither lies in the handling of very-high resolution datasets nor in dataintegration; the main focus of FHP_GTOPO30 is to provide an easy-to-use user-interface to allow geographically inexperienced users access to geo-referenced data on the web. 2. FHP_GTOPO30 USER-INTERFACE The user-interface of FHP_GTOPO30 is divided into two distinguished parts, corresponding to the two phases within a user session: area selection and area exploration. The first part,

2 called the selection interface is organized as an HTML-frame structure with three frames (zoom_0, zoom_1, zoom_2) and solely serves the precise selection of the world location to be later visualized as 3D VRML landscape. The second part, called the exploration interface is located in a separate Browser window ( vrml ) and serves the navigation and information display within the selected 3D VRML landscape. Figure 1 illustrates schematically this basic user-interface layout of the FHP_GTOPO30 application. (c) Figure 2: (a) -(c) Selection of world location in 3 steps. Figure 1: Basic layout of the FHP_GTOPO30 user-interface 2.1 The Selection Interface The first step within a FHP_GTOPO30 user session consists of selecting an area of interest to be generated and displayed as 3D landscape. Using 2D maps the selection process proceeds in three steps of discrete zooming as shown in figure 2. Starting with a map of the entire Earth at a resolution of 1 degree (i.e. each pixel corresponds to an area of 1x1 degree), the user first selects an area of 30x30 degree by simply dragging a selection rectangle to the desired world location (figure 2a). The corresponding zoom map has a resolution of 10 km and is displayed within the lower left frame zoom_1 (figure 2b). Repeating this step within the zoomed area the user finally selects an area of 3x3 degree which is displayed within the lower right frame zoom_2 (figure 2c). It has the same resolution as the GTOPO30 dataset itself, 1x1 km. Within the final zoom map the user selects the area from which the 3D VRML landscape should be generated. The preset size of the selection rectangle corresponds to an area of 100 square km but may be resized by pulling at its edges, up to 360 square km as shown in figure 3. This purely mouse-based drag-and-click selection mechanism, implemented by means of a Java applet, is intended to provide an easy-to-use interface to the GTOPO30 dataset, avoiding the need of any geographical knowledge like longitude/latitude coordinates on the user s side. (a) Figure 3: Resizing of the selection rectangle (b) The design of the selection interface described above is based on the principle of simultaneous representation of Overview-and- Detail identified as important in various fields of userinteraction, including geographical information systems [10, 11] and is thought to be especially useful for unexperienced (or curious) users to feel in full control of where they are and where

3 they want to go. As all zoom maps with the positions of the respective selection rectangles are kept and always visible to the user, he is able to identify his position with respect to the entire Earth at any time, thus supporting the feeling of absolute orientation. Furthermore, at each stage of the selection process the user may change his selection within any of the three maps and thus quickly browse completely different regions of the Earth without ever using a back-button. 2.2 Exploration Interface Once an area of interest has been defined by selection within the last zoom map the corresponding VRML-based elevation model is dynamically generated and displayed within a separate Browser window (labeled vrml in figure 1). Figure 4 shows the VRML-window of FHP_GTOPO30 with an elevation model of an area near Monterey, CA. Figure 4: Layout of the VRML window of FHP_GTOPO30 The upper two third of the window are reserved for the standard VRML-Browser (here: SGI Cosmoplayer) including the VRML display area and the Browser s standard navigation bar. There below the actual Java-based exploration interface is located, offering additional options for user-interaction and information display. The additional exploration interface becomes necessary because we want to provide functionalities not supplied by the standard user-interface of VRML-Browsers like dynamic, userdefined height scaling and loading of textures as well as additional means for navigation and user-orientation. The exploration interface is bound to the VRML scene by means of the so-called External Authoring Interface (EAI) allowing to integrate the advanced functionality of Java into VRML [12]. Figure 5 shows the exploration interface in more detail the different functionalities of which are discussed in the following subsections. Figure 5: The exploration interface of FHP_GTOPO D Overview Map With Position Marker A 2D overview map of the current VRML scene is placed on the left hand side of the exploration interface. A position marker (red circle with directed arrow) indicates the current position and viewing direction of the user. This element serves two purposes: first it is intended as an aid for a better user-orientation; the position marker within the overview map is adjusted automatically, whenever the user moves within the VRML landscape. This way the user may control his position within the global context at any time avoiding the phenomenon of getting lost in space. Additional positional information is provided to the user in the form of longitude/latitude coordinates, displayed right hand to the middle of the exploration interface. The second purpose of the 2D overview map is navigation: by clicking anywhere in the 2D overview map the user is directly transferred to the corresponding location within the VRML landscape Selection of Information Textures The GTOPO30 dataset form the basis for the VRML representation of information with geographical reference. Dependent on the question, it may be desirable, to switch between specific global information with geographical reference, e.g. precipitation data, temperature data, geological data, vegetation data, etc. and map them onto the 3D elevation model on-the-fly. The selection menu Database placed in the middle of the exploration interface allows for this rapid user-defined switching between different global information textures. For demonstration purposes three textures have been integrated: 'greyscale', 'shaded relief' and 'UMD vegetation'. While the greyscale and shaded relief textures, created on the basis of the raw GTOPO30 data set, are of little informative value and have been added for demonstration purposes only, UMD vegetation are false-color coded vegetation data of the Earth made publicly available by the University of Maryland, College Park [13]. Part of the Database selection menu are the options legend and Database info. The option Legend allows to provide a pop-up legend for information textures that are false-color coded and by the option Database info additional metadata of the information texture, such as data-provider or data-resource may be delivered. Figure 6a,b shows as an example the switching between greyscale and UMD vegetation textures, figure 6c shows Legend and Database info for the UMD vegetation dataset, where the latter is simply a hyperlink to the UMD vegetation Internet homepage.

4 (a) (b) Figure 6a,b: User-defined selection of information textures from Database menu: (a) greyscale and (b) UMD vegetation (c) Figure 6c: Display of texture legend (option Legend ) and texture meta-information (option Database info ) Variable Height Scaling (Exaggeration) In order to make terrain topography more visible, especially within regions of low height levels, the exploration interface allows for artificial height scaling of the VRML landscape (exaggeration) as shown in figure 7. By pressing the scrollbar on the right hand side of the exploration interface, the height scaling of the VRML landscape may be exaggerated up to a factor of 30, whereby the height position of the user within the VRML landscape is automatically adjusted. Figure 7: Height scaling of VRML landscape topography 2.3 Integration of Geo-Referenced Local Data The design of the FHP_GTOPO30 application allows for the flexible integration of external, geo-referenced local information into the VRML landscape: The positional tracking used within the exploration interface for navigation and user-orientation purposes (see 2.2.1) can be exploited to implement a kind of simple GPS-like information system that allows to provide the user with geo-referenced local information as he moves through the virtual environment. As a demonstrative example a city information service for the United States has been integrated into this prototype version of FHP_GTOPO30. Longitude/latitude coordinates of 23,789 US-cities were taken from the freely available U.S. Gazetteer Place and Zipcode Files from the U.S. Census Bureau [14] and brought into a format, that allows the fast decision which cities fall into the geographical area that the user has selected for VRML display. For each of these locations a Viewpoint-node as well as a ProximitySensor-node are inserted when the VRML-landscape is dynamically generated. The action connected with the respective ProximitySensor-nodes is a query to external online-services, e.g. search-engines like Google or Altavista. We experimented with queries like tourist information, hotel, skyline or exposition in combination with the respective city name and mostly got interesting results. However, not all query combinations make sense under all circumstances (for example when passing by New York, the combination skyline + new york works fine but skyline doesn t yield many hits when passing by a little village in the Midwest). So, for demonstration purposes the prototype of FHP_GTOPO30 links to a US-based city information online-service [15], which uses the same dataset from the U.S. Census Bureau as FHP_GTOPO30 itself. This yields less exciting but very reliable results. As implemented the geo-referenced city information is displayed under the following circumstances (note that by the time of this writing this feature works only for landscapes within the U.S. due to the restricted dataset available):

5 When in the course of free navigation through the VRML landscape a point is passed, for which a city information is available, a query is sent to the city information server at and the available information is displayed within a separate pop-up window. By using the viewpoint list option in the navigation bar of the VRML-Browser all cities located within the VRML landscape are listed and may be directly selected. When a city is selected the user is immediately moved to that location in the VRML landscape (the position marker in the 2D overview map is accordingly updated) and the respective city information is displayed in a separate pop-up window. Figure 8a shows the VRML-window (small) for a region near Monterey, CA together with the corresponding Viewpoint list, figure 8b shows the situation after selecting Monterey from the Viewpoint list: the user is moved to the location and the city information for Monterey is displayed in a separate pop-up window. 3. CONCLUSIONS AND OUTLOOK In this paper we described the prototype system FHP_GTOPO30, an application designed to allow easy-to-use access to georeferenced data on the web. Using the USGS GTOPO30 dataset the system dynamically generates VRML-based elevation models of user-defined areas and offers a powerful exploration interface to interact within the virtual environment. Using geo-referenced local data (city coordinates) FHP_GTOPO30 implements a kind of simple GPS-like information system within the generated VRML landscape. The prototype system could be extended in several ways, two of which should be mentioned: Flexibility with respect to the local information displayed: An input field could be provided that allows the user to define his own query terms to be used in conjunction with the georeferenced city names provided by the system, as well as the online-service to be queried. This extension would provide a kind of personalized virtual GPS-like information system. Possibility for users to add local information to the system: It should be possible to provide an HTML-form where a user can add information in an easy-to-use fashion, e.g. an URL, relevant to his current position within the virtual environment (which the system can detect automatically). This way a kind of steadily growing geo-information system could develop, collaboratively fed by many individuals. 4. ACKNOWLEDGEMENTS The authors wish to thank Michael Leben for his support in programming the EAI. This research was funded by the Stifterverband der Deutschen Wissenschaft. Parts of this work were carried out together with Paul Morin from the Department of Geology and Geophysics of the University of Minnesota. Figure 8a: City selection from the Viewpoint list Figure 10b: Automatic user movement and display of the respective city information (here: Monterey, CA) 5. REFERENCES [1] Gore, A. (1998). The Digital Earth: Understanding Our Planet in the 21 st Century. Speech delivered at the California Science Center (CSC), Los Angeles, CA. 31 January [2] [3] J. Stone. Geographic Information Systems. Online. 6/1998: [4] A. Lochter, R. Däßler and P. Morin. Interaktive Exploration. ix 10/ [5] [6] [7] [8] Reddy, M., Leclerc,Y.G., Iverson, L. and Bletter, N. (1999). TerraVision II: Visualizing Massive Terrain Databases using VRML. IEEE Computer Graphics and Applications, 19(2):

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