真实感三维地形造型及可视化

【作者】 侯波；

【导师】 张建中；

【作者基本信息】 电子科技大学 ， 计算机软件与理论， 2005， 硕士

【摘要】 三维地形模型和可视化技术在地理信息系统、数字城市、数字地球、虚拟仿真、飞行模拟和地面驾驶模拟、三维游戏等很多领域都有着重要的应用。怎样对地形这一自然界最复杂的景物进行准确建模和逼真的可视化是目前研究的热点和难点,本文就此问题做了如下研究:·对目前应用最广的等高线数字地图进行了分析,提出在等高线插值的过程中,利用等高线的先验知识进行内插的算法。此算法速度快,且插出的等高线质量高。·提出采用用户交互的半自动方式进行高程识别的方法。此方法不仅可靠,而且大大减少了用户对等高线赋高程值的工作量。·利用等高线的第4维属性,由网格点邻近的有限个点的高程来近似该网格点的高程,据此建立的算法复杂度为线性。·采用了双三次多项式(三次曲面)计算由等高线生成的规则数据场的插值,由于考虑了一阶偏导数与二阶混合导数,因而能保证相邻曲面之间的连续与光滑。·在分析了多种多分辨率模型的基础上,提出对整个地形进行分块,在块内采用与视点相关的基于二叉树的连续多分辨率模型对地形进行简化。经实验,该方法充分运用了人体的视觉原理,在逼真表现三维地形的同时,保证了交互的实时性。·通过对数字地形的几种数据模型的比较,提出了基于经验的规则网格数据分块及预读策略,实践证明该策略能很好地解决大幅面地图的实时浏览。·在分析了与视点相关自适应的四叉树和二叉树地形简化算法的基础上,采用一种改进的ROAM算法。新算法分别对屏幕空间误差计算、视野范围内的块的分辨率、节点的视锥体裁减、三角形分裂合并方法以及两帧间构造网格进行了优化,大大提高了显示的实时性。更多还原

【Abstract】 3D terrain has extensive application fields, such as Geographic Information System,digital city, digital earth, virtual reality, games and entertainment. At present, how torealize fine modeling and three dimension visualization of large scale complicate 3Dterrain based on great data is hot topic and difficulty of research. The followingstudies have been done around the problem.·After analyzing features of digital couture map that is very popular, a kind ofinterpolation method based on experience has been proposed, which is fast and highquality.·A method of semiautomatic user-dependent elevation identification has beenproposed, which is reliable and decrease dramatically user’s interaction comparedwith other methods.·According to contour feature(A point on couture line, except for its (x,y,z) value, hascharacteristic that it maybe locate on the same line with other points.), elevationvalues of mesh points are computed through their neighbors.·A method of interpolating 3D regular data field has been proposed. Free-curvesurface constructed by the method has its feature-boundary curves connecting eachtwo patches are c1 continuous.·A new kind of method has been proposed which first gets dynamic partition fromgrid and then in patch predigests terrain complexity through view-dependent bi-treebased on multi-resolution. It has proved smooth frame.·After the structural features of several data model of digital elevation model havebeen compared, dynamic partition and pre-reading algorithm experience-dependentbased on grid has been proposed. It has proved that this algorithm can solve real-timebrowse problem of large scale 3D terrain.·The comparison of quadric-tree with bi-tree predigesting adapting algorithmintroduces an amelioration of real-time optimally adapting mesh, which optimizesscreen space distortion computing, resolution of patch of grid in view frustum, nodeculling in frustum, triangle split and merge and mesh construction between frames.更多还原