Terrain Visualization

This study investigates and demonstrates the state of the art in remote sensing techniques for detailed landslide hazard assessment applicable to large areas. Since the most common methods of landslide hazard assessment using simple inventories and weighted overlays are heavily dependent on three-dimensional terrain visualization and analysis, stereo satellite images from the IKONOS Very High Resolution (VHR) sensor are used for this study. The DEMs created from IKONOS stereo images appear to be much more accurate and sensitive to micro-scale terrain features than a DEM created from digital contour data with a 2 m contour interval. Pan-sharpened stereo IKONOS images permit interpretation of recent landslides as small as 2-3 m in width as well as relict landslides older than 50 years. A cost-benefit analysis comparing stereo air photo interpretation with stereo satellite image interpretation suggests that stereo satellite imagery is usually more cost-effective for detailed landslide hazard assessment over large areas. D

Visual simulation of natural erosion on terrains has always been a fascinating research topic in the field of computer graphics. While there are many algorithms already developed to improve the visual quality of terrain, the recent simulation methods revolve around physically-based hydraulic erosion because it can generate realistic natural-looking terrains. However, many of such algorithms were tested only on low resolution terrains. When simulated on a higher resolution terrain, most of the current algorithms become computationally expensive. This is why in many applications today, terrains are generated off-line and loaded during the application runtime. This method restricts the number of terrains which can be stored if there is a limitation on storage capacity.

In this paper a new method is presented for 3-D terrain visualization via reversible JPEG2000-based blind data hiding with special focus on data synchronization and scalability. Online real-time 3-D terrain visualization involves considerable amount of data. The process is essentially the mapping of the aerial photograph, called texture, onto its corresponding digital elevation model (DEM) implying at least two distinct data inputs. The presence of large disparate data necessitates a compression strategy on one hand and the integration of the DEM and texture into one unit on the other. Whilst the compression must accommodate the scalability requirement originated by the diversity of clients, the unification of data ought to be synchronous. For scalability this paper relies on the multiresolution nature of the DWT-based JPEG2000 standard whereas the synchronized unification of DEM with the texture is realized by the application of a perceptually transparent data hiding strategy in the DWT domain. The proposed method is blind in the sense that only a secret key, if any, and the size of the original DEM are needed to extract the data from the texture image. We believe that this is one of the pioneering methods to propose scalable embedding of DEM in the texture image. The method is cost effective, in terms of memory and bandwidths, which is an advantage, especially, in real-time environments when quicker transfer of data is required. The results of a 3-D visualization simulation effected with our method were encouraging and gave a useful insight to the effectiveness of our method in various bandwidth scenarios.

We classify 3D aerial LiDAR scattered height data into buildings, trees, roads, and grass using the Support Vector Machine (SVM) algorithm. To do so we use five features: height, height variation, normal variation, LiDAR return intensity, and image intensity. We also use only LiDARderived features to organize the data into three classes (the road and grass classes are merged). We have implemented and experimented with several variations of the SVM algorithm with soft-margin classification to allow for the noise in the data. We have applied our results to classify aerial LiDAR data collected over approximately 8 square miles. We visualize the classification results along with the associated confidence using a variation of the SVM algorithm producing probabilistic classifications. We observe that the results are stable and robust. We compare the results against the ground truth and obtain higher than 90% accuracy and convincing visual results.

We present a technique for efficient management of large textures and its real-time application to geometric models. The proposed technique is inspired by the clipmap [12] idea, that caches in video memory a subset of the texture mipmap pyramid. Based on this concept, we define some structures and a different management allowing its implementation on a personal computer without specific graphics hardware. Finally, we present the results of the application in a terrain visualization system, using several simultaneous textures with a detail up to 0.25 meters per texel, covering a 60,000 km 2 area.

The Mars Pathfinder mission used a unique capability to rapidly generate and interactively display three-dimensional (3-D) photorealistic virtual reality (VR) models of the Martian surface. An interactive terrain visualization system creates and renders digital terrain models produced from stereo images taken by the Imager for Mars Pathfinder (IMP) camera. The stereo pipeline, an automated machine vision algorithm, correlates features between the left and right images to determine their disparity and computes the corresponding positions using the known camera geometry. These positions are connected to form a polygonal mesh upon which IMP images are overlaid as textures. During the Pathfinder mission, VR models were produced and displayed almost as fast as images were received. The VR models were viewed using MarsMap, an interface that allows the model to be viewed from any perspective driven by a standard three-button computer mouse. MarsMap incorporates graphical representations of the lander and rover and the sequence and spatial locations at which rover data were taken. Graphical models of the rover were placed in the model to indicate the rover position at the end of each day of the mission. Images taken by Sojourner cameras are projected into the model as 2-D "billboards" to show their proper perspective. Distance and angle measurements can be made on features viewed in the model using a mouse-driven 3-D cursor and a point-andclick interface. MarsMap was used to assist with archiving and planning Sojourner activities and to make detailed measurements of surface features such as wind streaks and rock size and orientation that are difficult to perform using 2-D images. Superresolution image processing is a computational method for improving image resolution by a factor of n 1/2 by combining n independent images. This technique was used on Pathfinder to obtain better resolved images of Martian surface features. We show results from superresolving IMP camera images of six targets including near-and far-field objects and discuss how the resolution improvement aids interpretation. Similar flood deposits can be seen on both of the Twin Peaks that cannot be resolved in raw images. Millimeter-sized pits are resolved on the rocks Wedge and Halfdome. Other rocks at the Pathfinder site exhibit fine-scale layering that is otherwise invisible. Use of the method resulted in the probable discovery of an artifact of intelligent life on Mars: a part of the Pathfinder spacecraft.

We describe two experimental desktop library clients that offer improved access to geospatial data via the Alexandria Digital Library (ADL): ArcADL, an extension to ESRI's ArcView GIS, and vtADL, an extension to the Virtual Terrain Project's Enviro terrain visualization package. ArcADL provides a simplified user interface to ADL's powerful underlying distributed geospatial search technology. Both clients use the ADL Access Framework to access library data that is available in multiple formats and retrievable by multiple methods. Issues common to both clients and future scenarios are also considered.

Game engines are relatively low-cost but powerful systems for creating and exploring virtual environments, and are increasingly used in the fields of architecture and urban planning. Traditionally urban planners and landscape architects used small-scale hand-modelled terrains. However, in order to increase both realism and modelling efficiency it is preferable to use computer generated terrains obtained from remote sensing data. Unfortunately many game engines are designed to use relatively small infinitely repeating terrain blocks. In this paper we analyse how the popular Torque terrain engine, which is used by the Department of Architecture of the University of Auckland, can be modified and extended for architectural purposes. The ultimate limitations of the terrain engine are identified and the terrain engine is evaluated on its suitability for architectural design. We explain how large scale terrains can be incorporated into the engine design and we propose a way to integrate th...

In this paper we present a novel approach for interactive rendering of large terrain datasets. Our approach is based on subdividing a terrain into rectangular patches at different resolutions. Each patch is represented by four triangular tiles that are selected form different resolutions, and four strips which are used to stitch the four tiles in a seamless manner. Such a scheme maintains resolution changes within patches through the stitching strips, and not across patches. At runtime, these patches are used to construct a level-of-detail representation of the input terrain based on view-parameters. A selected level of detail only includes the layout of the patches and their boundary edges resolutions. The layout includes the location and dimension of each patch. Within the graphics hardware, the GPU generates the meshes of the patches by using scaled instances of cached tiles and assigns elevation for each vertex from cached textures. Since adjacent rectangular patches agree on the resolution of the common edges, the resulted mesh does not include cracks or degenerate triangles. Our algorithm manages to achieve quality images at high frame rates while providing seamless transition between different levels of detail.

This paper describes the representation and navigation of large, multi-resolution, georeferenced datasets in VRML97. This requires resolving nontrivial issues such as how to represent deep level of detail hierarchies efficiently in VRML; how to model terrain using geographic coordinate systems instead of only VRML's Cartesian representation; how to model georeferenced coordinates to sub-meter accuracy with only single-precision floating point support; how to enable the integration of multiple terrain datasets for a region, as well as cultural features such as buildings and roads; how to navigate efficiently around a large, global terrain dataset; and finally, how to encode metadata describing the terrain. We present solutions to all of these problems. Consequently, we are able to visualize geographic data in the order of terabytes or more, from the globe down to millimeter resolution, and in real-time, using standard VRML97.

We present TanGeoMS, a tangible geospatial modeling visualization system that couples a laser scanner, projector, and a flexible physical three-dimensional model with a standard geospatial information system (GIS) to create a tangible user interface for terrain data. TanGeoMS projects an image of real-world data onto a physical terrain model. Users can alter the topography of the model by modifying the clay surface or placing additional objects on the surface. The modified model is captured by an overhead laser scanner then imported into a GIS for analysis and simulation of real-world processes. The results are projected back onto the surface of the model providing feedback on the impact of the modifications on terrain parameters and simulated processes. Interaction with a physical model is highly intuitive, allowing users to base initial design decisions on geospatial data, test the impact of these decisions in GIS simulations, and use the feedback to improve their design. We demonstrate the system on three applications: investigating runoff management within a watershed, assessing the impact of storm surge on barrier islands, and exploring landscape rehabilitation in military training areas.

Terrain visualization is a difficult problem for applications requiring accurate images of large datasets at high frame rates, such as flight simulation and ground-based aircraft testing using synthetic sensor stimulation. On current graphics hardware, the problem is to maintain dynamic, view-dependent triangle meshes and texture maps that produce good images at the required frame rate. We present an algorithm for constructing triangle meshes that optimizes flexible view-dependent error metrics, produces guaranteed error bounds, achieves specified triangle counts directly, and uses frame-to-frame coherence to operate at high frame rates for thousands of triangles per frame. Our method, dubbed Real-time Optimally Adapting Meshes (ROAM), uses two priority queues to drive split and merge operations that maintain continuous triangulations built from preprocessed bintree triangles. We introduce two additional performance optimizations: incremental triangle stripping and prioritycomputation deferral lists. ROAM execution time is proportionate to the number of triangle changes per frame, which is typically a few percent of the output mesh size, hence ROAM performance is insensitive to the resolution and extent of the input terrain. Dynamic terrain and simple vertex morphing are supported.

This paper discusses technical challenges and navigational skill requirements of mobile robots for traversable path planning in natural environments similar to Mars surface terrains. Different methods for detecting salient terrain features based on imaging texture analysis techniques are described. In particular, three competing soft computing techniques are presented for terrain traversability assessment: a rule-based terrain classifier, a neural network-based terrain classifier, and a fuzzy-logic terrain classifier. Each terrain classifier divides a region of natural terrain into finite subterrain regions and classifies terrain condition exclusively within each sub-terrain region based on terrain visual clues. Image processing techniques are applied for aggregative fusion of sub-terrain assessment results. Results of a comparative performance evaluation of all three terrain classifiers are presented. The last two terrain classifiers are shown to have remarkable capability for traversability assessment, which facilitates navigation in unstructured natural terrain environments.

This study investigates and demonstrates the state of the art in remote sensing techniques for detailed landslide hazard assessment applicable to large areas. Since the most common methods of landslide hazard assessment using simple inventories and weighted overlays are heavily dependent on three-dimensional terrain visualization and analysis, stereo satellite images from the IKONOS Very High Resolution (VHR) sensor are used for this study. The DEMs created from IKONOS stereo images appear to be much more accurate and sensitive to micro-scale terrain features than a DEM created from digital contour data with a 2 m contour interval. Pan-sharpened stereo IKONOS images permit interpretation of recent landslides as small as 2-3 m in width as well as relict landslides older than 50 years. A cost-benefit analysis comparing stereo air photo interpretation with stereo satellite image interpretation suggests that stereo satellite imagery is usually more cost-effective for detailed landslide hazard assessment over large areas. D

In this paper we present a novel approach for interactive rendering of large terrain datasets which is based on subdividing the terrain into rectangular patches at different resolutions. Each patch is represented by four triangular tiles which can be at different resolutions; and four strips which are used to stitch the four tiles in a seamless manner. As a result, our scheme maintains resolution changes within patches and not across patches. At runtime, the terrain patches are used to construct a level of detail based on view-parameters. The selected level of detail only includes the layout of the patches and the resolutions at boundary edges. Since adjacent patches agree on the resolution of common edges, the resulted mesh does not include any cracks or degenerate triangles. The GPU generates the meshes of the patches by using scaled instances of cached tiles and assigning elevation for each vertex from the cached textures. Our algorithm manages to achieve quality images at high frame rates while providing seamless transition between different levels of detail.

There is extensive knowledge on how to represent terrain using various relief depiction methods, such as hill shading and cliff drawing in cartographic products using large-scale maps. However, the relevance and correct use of topographic information nowadays in small-scale maps does not seem to be of high priority. This information that is frequently poorly depicted in such products can be

We present an elegant and simple to implement framework for performing out-of-core visualization and view-dependent refinement of large terrain surfaces. Contrary to the recent trend of increasingly elaborate algorithms for large-scale terrain visualization, our algorithms and data structures have been designed with the primary goal of simplicity and efficiency of implementation. Our approach to managing large terrain data also departs from more conventional strategies based on data tiling. Rather than emphasizing how to segment and efficiently bring data in and out of memory, we focus on the manner in which the data is laid out to achieve good memory coherency for data accesses made in a top-down (coarse-to-fine) refinement of the terrain. We present and compare the results of using several different data indexing schemes, and propose a simple to compute index that yields substantial improvements in locality and speed over more commonly used data layouts.

Our second contribution is a new and simple, yet easy to generalize method for view-dependent refinement. Similar to several published methods in this area, we use longest edge bisection in a top-down traversal of the mesh hierarchy to produce a continuous surface with subdivision connectivity. In tandem with the refinement, we perform view frustum culling and triangle stripping. These three components are done together in a single pass over the mesh. We show how this framework supports virtually any error metric, while still being highly memory and compute efficient.

The real-time rendering of arbitrarily large textures is a problem that has long been studied in terrain visualization. For years, different approaches have been published that have either expensive hardware requirements or other severe limitations in quality, performance or versatility. The biggest problem is usually a strong coupling between geometry and texture, both regarding database structure, as well as LOD

Virtual globes are becoming ubiquitous in the visualization of planetary bodies and Earth specifically. While many of the current virtual globes have proven to be quite useful for remote geologic investigation, they were never designed for the purpose of serving as virtual geologic instruments. Their shortcomings have become more obvious as earth scientists struggle to visualize recently released digital elevation models of very high spatial resolution (0.5-1 m 2 /sample) and extent ( 42000 km 2 ). We developed Crusta as an alternative virtual globe that allows users to easily visualize their custom imagery and more importantly their custom topography. Crusta represents the globe as a 30-sided polyhedron to avoid distortion of the display, in particular the singularities at the poles characteristic of other projections. This polyhedron defines 30 ''base patches,'' each being a four-sided region that can be subdivided to an arbitrarily fine grid on the surface of the globe to accommodate input data of arbitrary resolution, from global (BlueMarble) to local (tripod LiDAR), all in the same visualization. We designed Crusta to be dynamic with the shading of the terrain surface computed on-the-fly when a user manipulates his point-of-view. In a similarly interactive fashion the globe's surface can be exaggerated vertically. The combination of the two effects greatly improves the perception of shape. A convenient pre-processing tool based on the GDAL library facilitates importing a number of data formats into the Crusta-specific multi-scale hierarchies that enable interactive visualization on a range of platforms from laptops to immersive geowalls and caves. The main scientific user community for Crusta is earth scientists, and their needs have been driving the development. (T. Bernardin). Please cite this article as: Bernardin, T., et al., Crusta: A new virtual globe for real-time visualization of sub-meter digital topography at planetary scales. Please cite this article as: Bernardin, T., et al., Crusta: A new virtual globe for real-time visualization of sub-meter digital topography at planetary scales.

We present a technique for efficient management of large textures and its real-time application to geometric models. The proposed technique is inspired by the clipmap (12) idea, that caches in video memory a subset of the texture mipmap pyramid. Based on this concept, we define some structures and a different management allowing its implementation on a personal computer without specific

This paper is focused on the analysis of virtual representation of terrain through the web, and shows the steps to follow in order to put into practice a virtual interactive terrain visualization system. The recent developments of three-dimensional visualization systems can be naturally applied to terrain visualization targeted to the web, driving to a higher interaction level. Traditionally it has

The CECA VisLab is currently investigating the educational uses of a GeoWall 3D Stereo Rendering system. Many commercial and non-commercial programs are currently available for geographic virtual reality. We have explored the uses of one of these programs, Walkabout (under development by the Electronic Visualization Laboratory at the University of Illinois at Chicago), a program that allows the user to move in relationship to the data in X-Y-Z directions to explore the terrain. We discuss several enhancements for this 3D stereo terrain visualization tool: the ability to directly load Digital Elevation Model (DEM) files and the implementation of a Level of Detail Algorithm (LOD) that optimizes the data in order to increase rendering performance. We discuss the performance of the enhanced program with a data set of particular interest to us, the Tennessee River Gorge including nearby mountains and the Chattanooga, Tennessee metropolitan area.

I nterest in visualization has grown in recent years, producing rapid advances in the diversity of research and in the scope of proposed techniques. Much of the initial focus in computer-based visualization concentrated on display algorithms, often for specific domains. For example, volume, flow, and terrain visualization techniques have generated significant insights into fundamental graphics and visualization theory, aiding the application experts who use these techniques to advance their own research. More recent work has extended visualization to abstract data sets like network intrusion detection, recommender systems, and database query results. Although display algorithms are a critical component in the visualization process, they are not the only issue to consider. More and more, we see visualization as a path from data to understanding. From this perspective, two obvious questions arise: ■ What should we do before we display the data? ■ What can we do after the user views the data? This is not a new idea, of course. Our work is motivated by others in the community, including methods to integrate data management into visualization, metadata generation and management, techniques to preprocess data to extract and display critical details, and intelligent systems that help users design effective visu-alizations. This article describes our initial end-to-end system that starts with data management and continues through assisted visualization design, display, navigation, and user interaction (see Figure 1). The purposes of this discussion are to ■ promote a more comprehensive visualization framework; ■ describe how to apply expertise from human psychophysics, databases, rational logic, and artificial intelligence to visualization; and ■ illustrate the benefits of a more complete framework using examples from our own experiences.

We present TanGeoMS, a tangible geospatial modeling visualization system that couples a laser scanner, projector, and a flexible physical three-dimensional model with a standard geospatial information system (GIS) to create a tangible user interface for terrain data. TanGeoMS projects an image of real-world data onto a physical terrain model. Users can alter the topography of the model by modifying the clay surface or placing additional objects on the surface. The modified model is captured by an overhead laser scanner then imported into a GIS for analysis and simulation of real-world processes. The results are projected back onto the surface of the model providing feedback on the impact of the modifications on terrain parameters and simulated processes. Interaction with a physical model is highly intuitive, allowing users to base initial design decisions on geospatial data, test the impact of these decisions in GIS simulations, and use the feedback to improve their design. We demonstrate the system on three applications: investigating runoff management within a watershed, assessing the impact of storm surge on barrier islands, and exploring landscape rehabilitation in military training areas.

Terrain visualization is a difficult problem for applications requiring accurate images of large datasets at high frame rates, such as flight simulation and ground-based aircraft testing using synthetic sensor stimulation. On current graphics hardware, the problem is to maintain dynamic, view-dependent triangle meshes and texture maps that produce good images at the required frame rate. We present an algorithm for constructing triangle meshes that optimizes flexible view-dependent error metrics, produces guaranteed error bounds, achieves specified triangle counts directly, and uses frame-to-frame coherence to operate at high frame rates for thousands of triangles per frame.

GeoVRML 1.0 provides geoscientists with a rich suite of enabling capabilities that cannot be found elsewhere. That is, the ability to model dynamic 3-D geographic data that can be distributed over the web and interactively visualized using a standard browser configuration. GeoVRML includes nodes for VRML97 that perform this task; addressing issues such as coordinate systems, scalability, animation, accuracy, and preservation of the original geographic data. The implementation is released as open source and includes various tools for generating GeoVRML data. All these facilities provide geoscientists with an excellent medium to present complex 3-D geographic data in a dynamic, interactive, and web-accessible format. We illustrate these capabilities using real-world examples drawn from diverse application areas.

The Mars Pathfinder mission used a unique capability to rapidly generate and interactively display three-dimensional (3-D) photorealistic virtual reality (VR) models of the Martian surface. An interactive terrain visualization system creates and renders digital terrain models produced from stereo images taken by the Imager for Mars Pathfinder (IMP) camera. The stereo pipeline, an automated machine vision algorithm, correlates features between the left and right images to determine their disparity and computes the corresponding positions using the known camera geometry. These positions are connected to form a polygonal mesh upon which IMP images are overlaid as textures. During the Pathfinder mission, VR models were produced and displayed almost as fast as images were received. The VR models were viewed using MarsMap, an interface that allows the model to be viewed from any perspective driven by a standard three-button computer mouse. MarsMap incorporates graphical representations of the lander and rover and the sequence and spatial locations at which rover data were taken. Graphical models of the rover were placed in the model to indicate the rover position at the end of each day of the mission. Images taken by Sojourner cameras are projected into the model as 2-D "billboards" to show their proper perspective. Distance and angle measurements can be made on features viewed in the model using a mouse-driven 3-D cursor and a point-andclick interface. MarsMap was used to assist with archiving and planning Sojourner activities and to make detailed measurements of surface features such as wind streaks and rock size and orientation that are difficult to perform using 2-D images. Superresolution image processing is a computational method for improving image resolution by a factor of n 1/2 by combining n independent images. This technique was used on Pathfinder to obtain better resolved images of Martian surface features. We show results from superresolving IMP camera images of six targets including near-and far-field objects and discuss how the resolution improvement aids interpretation. Similar flood deposits can be seen on both of the Twin Peaks that cannot be resolved in raw images. Millimeter-sized pits are resolved on the rocks Wedge and Halfdome. Other rocks at the Pathfinder site exhibit fine-scale layering that is otherwise invisible. Use of the method resulted in the probable discovery of an artifact of intelligent life on Mars: a part of the Pathfinder spacecraft.

Terrain visualization is a difficult problem for applications requiring accurate images of large datasets at high frame rates, such as flight simulation and ground-based aircraft testing using synthetic sensor stimulation. On current graphics hardware, the problem is to maintain dynamic, view-dependent triangle meshes and texture maps that produce good images at the required frame rate. We present an algorithm for constructing triangle meshes that optimizes flexible view-dependent error metrics, produces guaranteed error bounds, achieves specified triangle counts directly, and uses frame-to-frame coherence to operate at high frame rates for thousands of triangles per frame.

We present an elegant and simple to implement framework for performing out-of-core visualization and view-dependent refinement of large terrain surfaces. Contrary to the trend of increasingly elaborate algorithms for large-scale terrain visualization, our algorithms and data structures have been designed with the primary goal of simplicity and efficiency of implementation. Our approach to managing large terrain data also departs from more conventional strategies based on data tiling. Rather than emphasizing how to segment ...

We present an interactive, real-time mapping system for use with digital elevation models and remotely sensed multispectral imagery that aids geoscientists in the creation and interpretation of geologic/neotectonic maps at length scales of 10 m to 1000 km. Our system provides a terrain visualization of the surface of the Earth or other terrestrial planets by displaying a virtual terrain model

The article describes a method for object and terrain visualization by means of the combination of two algorithms, one for terrain data and one for objects. Our purpose is to generate, efficiently and rapidly, aerial images of terrain with objects such as houses, ...

This paper describes an efficient technique for out-of-core rendering and management of large textured terrain surfaces. The technique, called Batched Dynamic Adaptive Meshes (BDAM) , is based on a paired tree structure: a tiled quadtree for texture data and a pair of bintrees of small triangular patches for the geometry. These small patches are TINs and are constructed and optimized off-line with high quality simplification and tristripping algorithms. Hierarchical view frustum culling and view-dependent texture and geometry refinement is performed at each frame through a stateless traversal algorithm. Thanks to the batched CPU/GPU communication model, the proposed technique is not processor intensive and fully harnesses the power of current graphics hardware. Both preprocessing and rendering exploit out-of-core techniques to be fully scalable and to manage large terrain datasets.

Five patients with favorable outcomes after a shunt operation in normal pressure hydrocephalus were analyzed with the aim of identifying consistent findings in a lumbar puncture (LP) test. The cases commonly showed improvement in at least one cognition and two gait LP parameters. We suggest that when judging the effects of LP on a shunt operation, the gait parameters need to be tailored to the gait status and the analyzed LP parameters should be evaluated at least twice at different times.

Geographical Information Systems (GIS) and three dimensional (3D) World Wide Web (WWW) applications usage are on the rise. The demand for online 3D terrain visualization for GIS data has increased. Current users demand for more complex data which have higher accuracy and realism. This is aided by the emergence of geo-browsers in the market which provide free service and also cater for the commercialized market. Other new technology driving the market is the use of software such as CityGML, Virtual Reality Markup Language (VRML)/ Entensive 3D (X3D), geoVRML, and Keyhole Markup Language (KML). These technologies also play an important role for this new era of online 3D terrain visualization. The aim of this paper is to implement the online 3D terrain visualization for GIS data by using VRML technology and launching the system into three different web servers. The data used for this system are contour data and high resolution satellite image (QUICKBIRD) for Universiti Putra Malaysia (U...

Digital terrain models constitute the base of terrain visualization applications, used to visualize in an easy and powerful way a great quantity of information obtained from the terrain, such as occurs in virtual terrain visualization systems, used to know and enjoy land, training simulations, determination of visual impacts, etc. But these models can also be used as the base for