一种四叉树地形渲染裂缝的改进消除算法

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。

基于二叉树和GPU的无缝地形场景渲染方法

设计了一种基于图形处理器(GPU)的无缝地形渲染方法。该方法基于二叉树构建多层次地形网格,该网格用基于行、列号的地形模板表示。在设计过程中,将高程数据转化为适于GPU读取的高程纹理图,再通过顶点纹理提取(VTF)技术从纹理图中采样出高程值用于渲染,整个过程在GPU端完成,提升了地形数据访问效率。同时,采用实时优化自适应网格(ROAM)算法的强制拆分法,通过控制相邻地形块的等级来消除裂缝。最后,采用TriangleStrip方式进行渲染,避免了相邻三角形中顶点坐标数据的重复传递,减少了传递到GPU的数据量。用两块地形数据对算法渲染效率进行了检验,并将算法与Clipmap算法进行了帧率对比。结果表明,该算法有效解决了分块数据的裂缝问题,达到了交互式地形渲染的要求。

基于LOD算法的大规模地形实时渲染技术优化

大规模室外地形渲染是数字战场仿真领域的关键技术之一。文中使用四叉树的LOD算法来进行大规模地形渲染,并针对地形渲染容易出现地形裂缝现象,给出了一种四叉树节点依据细节等级向四周扩展再分割的方法来解决裂缝现象。该方法基本上可以实现不同分辨率地形模块间的平滑过渡。

Surface Morphology of Soil Cracks in Yuanmou Dry-hot Valley Region,Southwest China

Surface morphology of soil cracks is one of the important factors influencing the water evaporation rate in cracked soil in Yuanmou Dry-hot Valley Region,Southwest China. Quantitative study of the complicated surface morphology of soil cracks is a prerequisite for further studies of soil-cracking mechanisms. The present paper establishes a quantitative indicator system by application of concepts and methods originating from Fractal Geometry and Network Analysis. These indicators can effectively express the complicated features of soil-crack network structure. Furthermore,a series of values related to soil-crack morphology was obtained by image processing on field photos of soil-crack quads,and gradation criteria for the degree of development of soil cracks were determined. Finally,the changes in values of the morphological indicators under different degrees of development were analyzed in detail. Our results indicate that (1) the degree of development of soil cracks can be divided into five grades,i.e.,feeble development,slight development,medium development,intensive development and extremely intensive development; (2) the values of the indicators change predictably with increasing degree of development of soil cracks. The area density (Dc) increases,and both the area-weighted mean ratio of crack area to perimeter (AWMARP),which reflects the intensity of cracking,and the index r,which is related to the connectivity of a soil crack,grow uniformly (albeit with different forms). AWMRAP increases at a geometric rate while r shows logarithm-mic growth,indicating a gradual increase in theconnectivity of a soil crack. Nevertheless,the area-weighted mean of soil-crack fractal dimension (AWMFRAC) shows a decreasing trend,indicating a gradual decline in the complexity of cracks as area density increases.

Mechanism of formation of sliding ground fissure in loess hilly areas caused by underground mining

Based on a shallow-buried coal seam covered with thick loose layers in hilly loess areas of western China,we developed a mechanical model for a mining slope with slope stability analysis, and studied the mechanism of formation and development of a sliding ground fissure by the circular sliding slice method.Moreover, we established a prediction model of a sliding fissure based on a mechanical mechanism,and verified its reliability on face 52,304, an engineering example, situated at Daliuta coal mine of Shendong mining area in western China. The results show that the stress state of a mining slope is changed by its gravity and additional stress from the shallow-buried coal seam and gully terrain. The mining slope is found to be most unstable when the ratio of the down-sliding to anti-sliding force is the maximum, causing local fractures and sliding fissures. The predicted angles for the sliding fissure of face 52,304 on both sides of the slope are found to be 64.2° and 82.4°, which are in agreement with the experimental data.

Simulation of Morphological Development of Soil Cracks in Yuanmou Dry-hot Valley Region, Southwest China

Soil cracking is an important process influencing water and solutes transport in the Yuanmou Dry-hot Valley region of Southwest China. Studying the morphological development of soil cracks helps to further reveal the close relationship between the soil cracking process and water movement in such semi-arid regions. Here we report regular changes on surface morphology of soil cracks with decreasing water in four different soils (Typ-Ustic Ferrisols,Ver-Ustic Ferrisols,Tru-Ustic Vertisols and Typ-Ustic Vertisols) through simulation experiments. Our results indicate the following: 1) Different soils ultimately have different development degrees of soil cracks,according to their various values of crack area density. Soil cracks in Typ-Ustic Ferrisols can only develop to the feeble degree,while those in the other three soils are capable of developing into the intensive degree,and even into the extremely intensive degree. 2) Soil crack complexity,as expressed by the value of the area-weighted mean of crack fractal dimension (AWMFRAC),is found to continuously decrease as a whole through the whole cracking process in all the studied soils. 3) Soil crack connectivity shows a uniform trend in the studied soils,that is to say,connectivity gradually increases with soil crack development.

Fluid flow on centimeter-scale in deep paleosubduction zones in western Tianshan,China:Evidence from high-pressure veins

High-pressure(HP)veins were extensively developed in western Tianshan high-pressure(HP)metamorphic belt.The HP vein and host-rocks were analyzed by electronic microprobe to trace the origin of vein-forming fluids.Analytical data show that the immediately adjacent host-rocks of the studied HP vein are eclogites and gradually turned into blueschist as the distance from the veins increases,which indicates that the vein-forming fluid was derived from adjacent host-rocks;the boundaries between the vein and the host-rocks are sharp,which indicates that the fracture of the host-rocks is brittle during the vein-forming process.It is suggested that this type of HP veins is precipitated from the liquid formed by the dehydration of the host-rocks during the prograde metamorphism from blueschist to eclogite facies,which results in hydrofracturing of the rocks and provides the space for the vein to precipitate.The width of the eclogite-facies host-rocks is usually 1-2 cm,which provides the direct evidence that the fluid flow is on centimeter-scale.

THRUST NAPPE STRUTRUE IN THE JINGGANG MOUNTAIN: CHARACTERISTICS AND SIGNIFICANCE FOR PROSPECTION OF ORE DEPOSITS

Nappe structure, as was first discovered by the authors during the regional geological survey at the scale of 1:50,000 in The Jinggang Mountain, is mainly comprised of a series of NNE-NE-striking thrust fault zones and thrust sheets among them. Sinian, Cambrian, Ordovician, Devonian, Carboniferous,Triassic, Jurassic and Cretaceous strata are involved in the thrust nappe system. The nappe structure is of the type of duplex structures formed as a result of the earlier stage migration from SE to NW and late stage migration from E to W of sedimentary cover or basement strata. Formation of the nappe structure in the studied area involves two main epochs: Early Yanshanian and Late Yanshanian to Early Himalayan. The mineral deposits and the buried coalfields in the area, especially the latter, are extensively controlled by the nappe structure.