VRVis Project 2001: Quad-Tree based Terrain Rendering
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Shortly after finishing my diploma thesis in September 2001 I had some time to work for the Graz branch of the VRVis research center (Kompetenzzentrum für Virtual Reality und Visualisierung). More specifically I worked for AR2 (Application Research 2: Virtual Habitats) which is lead by Dr. Konrad Karner. AR2 works on a city scanner application being able to move around in a city like e.g. Graz taking photos of the facades, and fully automatically reconstruct the city (camera self-calibration, automatic feature extraction and image orientation). The reconstructed scene is visualized in a sophisticated rendering application which communicates with a database holding the large amount of data and a frame-rate controlled render setup based on hierarchical data-structures and numerical optimization procedures.
My task in this environment was to write a software tool for DI Christopher Zach who is responsible for the AR2 work package Data Management and Visualization. The tool should incorporate a 2,5D height-field and a corresponding texture (satellite images of a region or a city) into his frame-rate controlled setup.
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| Styrian flyover rendered with quad-tree based LoD, showing Aichfeld | |
The features of the C++ software tool are:
- breaking up of large height-fields and textures in smaller pieces at different Levels of Detail
- i.e. a 4096x4096 texture could be split into 16x16 tiles of length 256x256 pixels and 4 adjacent tiles could be smoothed, resampled and combined to form a scarcer level of detail
- the breaking up leads to a hierarchical quad-tree data structure
- the quad-tree is written to a file-system based database
- a rendering tool for Windows or Linux using OpenInventor reads the quad-tree from the database and visualizes it
- view-frustum culling is easily performed due to quad-tree structure, this speeds up the rendering
- it is possible that adjacent tiles with differing levels of detail are rendered, so to prevent crack edges a simple retriangulation scheme at the adjacency regions was implemented
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| Styrian flyover rendered with quad-tree based LoD, showing Upper-Styrian mountains | |
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| Styrian flyover rendered with quad-tree based LoD, showing Graz | |
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© 2005 by Martin Urschler
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