A new method for constructing contours from complicated terrain elevation grids containing invalid data is put forward. By using this method, the topological consistency of contours in groups can be maintained effecti...A new method for constructing contours from complicated terrain elevation grids containing invalid data is put forward. By using this method, the topological consistency of contours in groups can be maintained effectively and the contours can be drawn smoothly based on boundaries pre-searching and local correction. An experimental example is given to demonstrate that the contours constructed by this method are of good quality.展开更多
Incremental LOD can be transmitted on the network as a stream, then users on the clients can easily catch the skeleton of terrain without downloading all the data from the server. Detailed information in a local part ...Incremental LOD can be transmitted on the network as a stream, then users on the clients can easily catch the skeleton of terrain without downloading all the data from the server. Detailed information in a local part can be added gradually when users zoom it in without redundant data transmission in this procedure. To do this, an incremental LOD method is put forward according to the regular arrangement of grid. This method applies arbitrary sized grid terrains and is not restricted to square ones with a side measuring 2 k + 1 samples. Maximum height errors are recorded when the LOD is preprocessed and it can be visualized with the geometrical Mipmaps to reduce the screen error.展开更多
针对格网DEM难以对黄土高原梯田地形进行有效数字表达的问题,基于面向对象思想提出了能够顾及梯田地形的Grid-TIN混合格网DEM(Grid-TIN based DEM,GT-DEM)概念及其数据模型,并阐明其主要特征及与传统DEM的关系。以陕西绥德县辛店沟小流...针对格网DEM难以对黄土高原梯田地形进行有效数字表达的问题,基于面向对象思想提出了能够顾及梯田地形的Grid-TIN混合格网DEM(Grid-TIN based DEM,GT-DEM)概念及其数据模型,并阐明其主要特征及与传统DEM的关系。以陕西绥德县辛店沟小流域水平梯田为例,利用现有1∶1万格网DEM、梯田特征点线及其外围边界线,构建出能够充分顾及梯田地形的GT-DEM。研究表明,利用现有格网DEM和梯田地形特征点线构建顾及梯田地形GT-DEM的技术可行。GT-DEM不仅可对研究区全局地形进行粗略表达,而且可对其局部梯田地形进行精细表达。该研究是对如何提高DEM的梯田地形数字表达能力的有益探索,对进一步提高DEM对淤地坝、鱼鳞坑等其他人工地形的数字表达能力具有重要借鉴意义。展开更多
Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectra...Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectral energy decreases with decreasing wavelength, in spite of several departures. This relationship is approximated by an exponential function. A power law relationship between the terrain height spectra and wavelength is fitted by the least-squares method, and the fitting slope is associated with grid-size selection for mesoscale models. The monotonicity of grid size is investigated, and it is strictly proved that grid size increases with increasing fitting exponent, indicating that the universal grid size is determined by the minimum fitting exponent. An example of landslide-prone areas in western Sichuan is given, and the universal grid spacing of 4.1 km is shown to be a requirement to resolve 90% of terrain height variance for mesoscale models, without resorting to the parameterization of subgrid-scale terrain variance. Comparison among results of different simulations shows that the simulations estimate the observed precipitation well when using a resolution of 4.1 km or finer. Although the main flow patterns are similar, finer grids produce more complex patterns that show divergence zones, convergence zones and vortices. Horizontal grid size significantly affects the vertical structure of the convective boundary layer. Stronger vertical wind components are simulated for finer grid resolutions. In particular, noticeable sinking airflows over mountains are captured for those model configurations.展开更多
在大地形三维多分辨率显示中,针对裂缝消除问题提出了一种基于LOD(Level of Detail)控制和裂缝可视性的改进算法。证明在四叉树网格可视距离/尺寸比>3时,必然满足限制四叉树约束;基于裂缝的可见性,在预处理阶段通过区分地形上升裂缝...在大地形三维多分辨率显示中,针对裂缝消除问题提出了一种基于LOD(Level of Detail)控制和裂缝可视性的改进算法。证明在四叉树网格可视距离/尺寸比>3时,必然满足限制四叉树约束;基于裂缝的可见性,在预处理阶段通过区分地形上升裂缝和地形下降裂缝,为后者添加与裂缝大小一致的几何图形来生成裂缝消除补丁;在实时渲染过程中,既不需要通过CPU计算来控制网格的层次差,也不需要通过CPU来识别相邻网格层次差和消除裂缝。实验测试表明:该算法简单有效,附加网格数据比裙边算法减少约75%,且完全能够避免地形裂缝的显示。展开更多
文摘A new method for constructing contours from complicated terrain elevation grids containing invalid data is put forward. By using this method, the topological consistency of contours in groups can be maintained effectively and the contours can be drawn smoothly based on boundaries pre-searching and local correction. An experimental example is given to demonstrate that the contours constructed by this method are of good quality.
文摘Incremental LOD can be transmitted on the network as a stream, then users on the clients can easily catch the skeleton of terrain without downloading all the data from the server. Detailed information in a local part can be added gradually when users zoom it in without redundant data transmission in this procedure. To do this, an incremental LOD method is put forward according to the regular arrangement of grid. This method applies arbitrary sized grid terrains and is not restricted to square ones with a side measuring 2 k + 1 samples. Maximum height errors are recorded when the LOD is preprocessed and it can be visualized with the geometrical Mipmaps to reduce the screen error.
文摘针对格网DEM难以对黄土高原梯田地形进行有效数字表达的问题,基于面向对象思想提出了能够顾及梯田地形的Grid-TIN混合格网DEM(Grid-TIN based DEM,GT-DEM)概念及其数据模型,并阐明其主要特征及与传统DEM的关系。以陕西绥德县辛店沟小流域水平梯田为例,利用现有1∶1万格网DEM、梯田特征点线及其外围边界线,构建出能够充分顾及梯田地形的GT-DEM。研究表明,利用现有格网DEM和梯田地形特征点线构建顾及梯田地形GT-DEM的技术可行。GT-DEM不仅可对研究区全局地形进行粗略表达,而且可对其局部梯田地形进行精细表达。该研究是对如何提高DEM的梯田地形数字表达能力的有益探索,对进一步提高DEM对淤地坝、鱼鳞坑等其他人工地形的数字表达能力具有重要借鉴意义。
基金supported by the Key Research Program of the Chinese Academy of Sciences (Grant No. KZZD-EW-05-01)the special grant (Grant No. 41375052) from the National Natural Science Foundation of Chinafunded by an open project of the State Key Laboratory of Severe Weather (Grant No. 2013LASW-A06)
文摘Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectral energy decreases with decreasing wavelength, in spite of several departures. This relationship is approximated by an exponential function. A power law relationship between the terrain height spectra and wavelength is fitted by the least-squares method, and the fitting slope is associated with grid-size selection for mesoscale models. The monotonicity of grid size is investigated, and it is strictly proved that grid size increases with increasing fitting exponent, indicating that the universal grid size is determined by the minimum fitting exponent. An example of landslide-prone areas in western Sichuan is given, and the universal grid spacing of 4.1 km is shown to be a requirement to resolve 90% of terrain height variance for mesoscale models, without resorting to the parameterization of subgrid-scale terrain variance. Comparison among results of different simulations shows that the simulations estimate the observed precipitation well when using a resolution of 4.1 km or finer. Although the main flow patterns are similar, finer grids produce more complex patterns that show divergence zones, convergence zones and vortices. Horizontal grid size significantly affects the vertical structure of the convective boundary layer. Stronger vertical wind components are simulated for finer grid resolutions. In particular, noticeable sinking airflows over mountains are captured for those model configurations.
文摘在大地形三维多分辨率显示中,针对裂缝消除问题提出了一种基于LOD(Level of Detail)控制和裂缝可视性的改进算法。证明在四叉树网格可视距离/尺寸比>3时,必然满足限制四叉树约束;基于裂缝的可见性,在预处理阶段通过区分地形上升裂缝和地形下降裂缝,为后者添加与裂缝大小一致的几何图形来生成裂缝消除补丁;在实时渲染过程中,既不需要通过CPU计算来控制网格的层次差,也不需要通过CPU来识别相邻网格层次差和消除裂缝。实验测试表明:该算法简单有效,附加网格数据比裙边算法减少约75%,且完全能够避免地形裂缝的显示。
