Virtual 3D Campus for Universiti Teknologi Malaysia (UTM)

University campuses consists of many buildings within a large area managed by a single organization. Like 3D city modeling, a 3D model of campuses can be utilized to provide a better foundation for planning, navigation and management of buildings. This study approaches 3D modeling of the UTM campus by utilizing data from aerial photos and site observations. The 3D models of buildings were drawn from building footprints in SketchUp and converted to CityGML using FME software. The CityGML models were imported into a geodatabase using 3DCityDB and visualized in Cesium. The resulting 3D model of buildings was in CityGML format level of detail 2, consisting of ground, wall and roof surfaces. The 3D models were positioned with real-world coordinates using the geolocation function in SketchUp. The non-spatial attributes of the 3D models were also stored in a database managed by PostgreSQL. While the methodology demonstrated in this study was found to be able to create LoD2 building models. However, issues of accuracy arose in terms of building details and positioning. Therefore, higher accuracy data, such as point cloud data, should produce higher LoD models and accurate positioning.

Influence of incident angle and laser footprint on precision and level of detail in terrestrial laser scanner measurements

Terrestrial laser scanners (TLS) are used for a variety of applications, e.g., surveying, forestry, cultural heritage preservation, mining, topographic mapping, urban planning, forensics etc. This technology has made a huge shift in 3D spatial data collection due to much faster speed compared to other techniques. In the absence of guiding principles for positioning TLS relative to an object, surveyors collect data at maximum arrangements of scanning geometry elements due to fear of incomplete data of TLS. In 3D spatial data acquisition, positional accuracy and Level of Detail (LOD) are major considerations and are dependent on laser incident angle, footprint size, range and resolution. Mathematical models have been developed relating range, incident angle and laser footprint size for different surface configurations. These models can be used to position TLS to collect data at required positional accuracy and LOD. Models have been verified by deriving one model from other surface models by changing parameters. Effects of incident angle and footprint size have been studied mathematically and experimentally on a natural sloping surface. From the results, surveyors can plan the positioning of the scanner so that data is collected at the required accuracy and LOD.

Method for 3D City Building Continuous Transformation Based on an Improved LOD Topological Data Structure

A 3D city model is an intuitive tool that is used to describe cities. Currently, level-of-detail (LOD) technology is used to meet different visual demands for 3D city models by weighting the rendering efficiency against the details of the model. However, when the visual demands change, the “popping” phenomenon appears when making transformations between different LOD models. We optimized this popping phenomenon by improving the data structure that focuses on 3D city building models and combined it with the facet shift algorithm based on minimal features. Unlike generating finite LOD models in advance, the proposed continuous LOD topology data structure is able to store the changes between different LOD models. By reasonably using the change information, continuous LOD transformation becomes possible. The experimental results showed that the continuous LOD transformation based on the proposed data structure worked well, and the improved data structure also performed well in memory occupation.

Automatic LOD selection using viewpoint entropy

Discrete Level of Detail (LOD) strategy is an effective solution for balancing the inherent contradiction between quality and speed in computer graphics. However, application of this strategy requires both the appropriate selection approach and the visually comfortable transition procedure to reduce the popping effects introduced by switching between different levels. In this paper, a novel automatic LOD selection method based on viewpoint entropy was proposed. Firstly, the traditional calculation method of viewpoint entropy contained in a scene was improved for the preprocessing of LOD models. Then, the runtime rendering scheme combined with our selection method was designed for balance of frame rate during real-time rendering, and a novel smoothing LOD transition strategy based on Alternate Frame Rendered (ALR) was put forward for elimination of popping effects. Finally, an example of complex scene combined with our proposal was researched to verify its real-time performance and ability in holding continuity of rendered images. Experimental studies show the effectiveness for stabilizing frame rate and improvements in reducing loss of continuity.

Real-Time Rendering Algorithm Based On Hybrid Static And Dynamic Simplification Methods

Level of detail (LoD) method is a key technique for real-time rendering. The generation algorithms of LoD models may be divided into two categories: static or view-independent algorithms and dynamic or view-dependent algorithms, each has its own advantages and drawbacks. This paper presents a new realtime rendering algorithm incorporating both of the two kinds. We simplify polygonal models viewindependently according to a user-specified approximation error first. Then the simplified models are used in a view-dependent real-time rendering algorithm. The paper presents a new view-dependent realtime mesh simplification algorithm. The algorithm can produce simplified models in real time while controlling the rendering pixel error. Examples illustrate efficiency of the algorithm.