数字地形编辑是虚拟地理环境、三维景观仿真系统中一个重要的研究内容,在城市与乡村、区域道路网、风景园林的数字化规划设计实践中具有重要价值。本文以规则格网的数字地形为研究对象,面向城市和园林景观规划设计中的实际应用,提出了交互式数字地形编辑的解决方案,重点给出了分页技术的地形交互式编辑具体过程和相关的主要实现技术。数字地形编辑的实现,首先,通过鼠标交互式操作,结合射线求交算法,在地形表面选取目标编辑区域;然后,结合夹角之和检测算法,获取区域下地形数据,设定新的地形高程值,最后,将编辑操作传输至地形其他层,更新整个地形,并在地形编辑后,采用方格网计算法,统计出区域下地形填挖方量。此外,在经过平整的地形区域,植入树和三维建筑模型,构建虚拟城镇小区景观。本文初步实现了编辑操作功能的计算机软件,并展示了数字地形编辑在城镇小区景观设计中的应用结果。试验表明,基于规则格网和分页技术的数字地形编辑方法具有算法简单、计算量小、易实现等特点。此外,通过鼠标交互式的操作,能够实时、直观地显示编辑结果,达到"所见即所得"的效果。
Digital terrain editing is one of important research contents in virtual geographical environment and 3D landscape simulation system, which has significant value in digital design practices of city and country, road network, landscape planning, etc. In this article we took the digital terrain based on regular grid as research objectives, oriented to practical application of the city and landscape planning & design, and proposed an interactive digital terrain editing scheme. OpenSceneGraph uses the directed acyclic graph for managing the scene graph, level of detail (LOD) and pagination technique for real-time rendering. Specific processes and related major implementation technology of the terrain interactive editing based on pagination technology was described. Firstly, the target region was selected through the mouse interactive operation combined with ray intersection algorithms. Secondly, the grid data under the region was gotten in the basis of polygon angle sum algorithm. Lastly, the grid elevation of region was assigned a new elevation value by dragging of mouse in the vertical direction. Under the edited region, by the grid method that is used to calculate earthwork volume, it is calculated that the volume of the fills and the excavations. In addition, the trees models were loaded by modeling software of ParaTree, which is researched and developed by our group, and the three-dimensional architectural models were built by the 3DMAX. All the models were loaded into the virtual forest visualization system (VisForest). The virtual town/village landscape in the flattened region was constructed according to user's design idea. The editing function was preliminarily realized, which showed the results of application in urban residential landscape design. This study showed that the digital terrain editing based on regular grid and pagination technology has advantages of simple algorithm, small amount of calculation and easy to realize. What is more, mouse interactive operation can show the editing result in a real-time and intuitional way, and achieve the effect of "what you see is what you get".
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