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Modeling the 3d terrain Effect on MT by the Boundary Element Method

Journal of China University of Geosciences 2006年第2期17卷 163-167页

作者：阮百尧徐世浙徐志锋 department of Resources &Environmental Engineering Guilin University ofTechnology department of Geosciences Zhejiang University department of Resources &Environmental Engineering Guilin University of Technology

A numerical method is put forward in this paper, using the boundary element method （BEM） to model 3d terrain effects on magnetotelluric （MT） surveys, Using vector integral theory and electromagnetic field boundary conditions, the boundary problem of two electromagnetic fields in the upper half space （air） and lower half space （earth medium） was transformed into two vector integral equations just related to the topography ： one magnetic equation for computing the magnetic field and the other electrical equation for computing the electrical field. The topography integral is decomposed into a series of integrals in a triangle element. For the integral in a triangle element, we suppose that the electromagnetic field in it is the stack of the electromagnetic field in the homogeneous earth and the topography response which is a constant; so the computation becomes simple, convenient and highly accurate. By decomposition and computation, each vector integral equation can be calculated by solving three linear equations that are related to the three Cartesian directions. The matrix of these linear equations is diagonally dominant and can be solved using the Symmetric Successive Over-Relaxation （SSOR） method. The apparent resistivity curve of MT on two 3d terrains calculated by BEM is shown in this paper.

关键词： 3d terrain MT boundary element method numerical modeling.

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Large-Scale terrain Simplification and Visualization Based on TIN

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Computer Aided drafting,design and Manufacturing 2008年第2期18卷 1-8页

作者： KANG Lai, WU Ling-da, YANG Bing, SONG Han-chen (College of Information Systems & Management, National University of defense Technology, Changsha 410073, China)

In the preprocessing phase, the global terrain model is partitioned into blocks with their feature points being picked out to generate TIN model for each terrain block, then the multi-resolution models of terrain organized in the form of quad-tree is created bottom-up. Cracks between terrain blocks are avoided by inserting vertices to form common boundaries. At run-time, a view-dependent LOd algorithm is used to control the loading and unloading of the proper blocks by an additional synchronous thread. To eliminate the artifacts created by LOd transitions, geomorphing is used in real-time. These rendering strategies increase the throughput of GPU and avoid imbalance of load among CPU, GPU and disk I/O. Experimental results show that the system can perform visually smooth rendering of large-scale terrain scenes with fine quality at an average rate of 80 fps.

关键词： real-time rendering 3d terrain multi-resolution triangulated irregular network quad-tree

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