The Research And Implementation Of Terrain Merging Based On 3D Mesh

No battlefield environment, there will be no war, but the traditional sense of the battlefield environment is real, objective world of space, and a simulation of the battlefield environment is a virtual space, through the computer, Internet, as well as related hardware and software Simulation of the real world. To put it simply, virtual terrain simulation is the application of virtual reality technology in the digital map on the basis of established, realistic description of the phenomenon of the Earth's surface and its real-time, interactive 3D terrain scenes.First Virtual battlefield terrain and the requirements of the current war with the increase in the complexity of the need to have more and more of the terrain, but the number of digital terrain in the real world is limited, and unable to meet the needs of modern virtual war, and terrain which generated by Terrain Editor needs much time and manpower, because of the above reasons, this paper proposes using of the advantages of computers,and a wealth of existing digital terrain resources through existing digital terrain resources to achieve the terrain by using terrain merging algorithms.In this paper, first it introduces the technologies the paper used ,VRML and DirectX, VRML is a abbreviations, and its English name is Virtual Reality Modeling Language, VRML is a new technology which relates to multimedia, the Internet, virtual reality and other fields, its basic aim is to establish interactive 3D multimedia on the Internet, VRML provides an efficient file format of description of simple and complex 3D objects and scenes, is the expansion of the World Wide Web is in the three-dimensional, DirectX is an application program interface, which allows the windows as a platform for games or multimedia procedure achieving higher efficiency, enhance graphics and sound 3d effects, and to provide a common design standard hardware drivers, game developers will not be required for each brand of hardware to write different drivers, but also lowers the user to install and set up the hardware complexity. Then it introduces judging-ray intersection with the mesh function in DirectX, as well as the algorithms and implementation of the principle.Mesh Zipper algorithm presents a method of combining multiple views of an object, captured by a range scanner, and assembling these views into one unbroken polygonal surface. The core of the algorithm is the Zipper algorithm. Zipper algorithm main course, the first two mesh remove redundant triangle, in trying to merge the two mesh, we eat away at the boundaries of both meshes until they just meet, we remove redundant triangle in each mesh, and then clips mesh, the mesh will be one of the border triangle divided into a mesh of other parts of the border were discarded, and the remaining part was retained, the final part is removing small triangles formed by the clipping process, The clipping process can introduce arbitrarily small or thin triangles into a mesh. For many applications this does matter, but in situations where such triangles are undesirable they can easily be removed. We use vertex deletion to remove small triangles: if any of a triangle's altitudes fall below a user-specified threshold we delete one of the triangle's vertices and all the triangles that shared this vertex. The above is a foreign algorithm; there is a domestic merger mesh algorithm - Mesh Stitch, mesh suture. Mesh Zipper and similar to the algorithm is directly in the mesh processing, but it does not cut another border triangle of the mesh in boundary with the boundary of other mesh, but create a suture line as the common boundary of meshes will be merged, and then link meshes seamlessly which will be merged as the suture line for skeleton structure. The process will be like the process of two fabrics stitching up, so it is called mesh image stitching.Finally, this paper introduces the terrain merging algorithm design and implementation, first of all, analysis the VRML file using VRML syntax explanation , read out the vertex and the surface information, and then use DirectX rendering to the screen, then determine the ultimate location of two terrain by inputting, start merging, In order to determine the intersection of the two terrain, we generate the bounding box for terrains. Several commonly used bounding box, Axis Aligned Bounding Box,Sphere,Oriented Bounding Box,Discrete Orientation Polytope . In this paper, we choose AABB to judge intersection, according to the vertex of each terrain information set out in each of their smallest AABB bounding box, and then determine whether or not these two bounding box intersect, and if the intersection obtained two bounding box intersection that posed by the part of the bounding box, in this bounding box identified in the vertex of each mesh to another mesh of the relative position, that is the top of the mesh or the bottom of the mesh. The judgment is mainly used D3DXIntersect function to achieve, and if the vertex will no longer be required and then the vertex removed, then structure AABB tree for the remaining triangular on the mesh, commonly used are top-down and bottom-up methods. In this paper we choose top-down to structure AABB tree, An AABB tree is constructed top-down, by recursive subdivision. At each recursion step, the smallest AABB of the set of primitives is computed, and the set is split by ordering the primitives with respect to a well-chosen partitioning plane. This process continues until each subset contains one element. Thus, we structure an AABB tree. Then introduced the triangle and AABB tree intersection rapid detection algorithm, which is based on separation axis theory, the algorithm used to judge whether triangle intersect with node. Then introduces the method to test whether the triangle intersect with another triangle, There are many methods to test whether the triangle intersect with another triangle, a traditional brute-force method, the basic tenets of a triangle for every one side of each triangle with the other side, if there is the intersection, the two intersecting triangles, is less efficient detection, and quick comparison The measuring principle is that each triangle because it is in a subset of the plane, if the two intersecting triangles, and the two will cross the plane of the intersection. Here introduces two ways, first, the scalar test, and adopted specific calculation of the triangular plane to the distance of each other as well as with the intersection of the plane formed by the line spacing value judgment on whether the triangular intersection. Another is vector test, vector test through a fixed point of the triangle determinant of plus or minus to judge the significance of the geometric triangle point, line and plane relationship between the relative position to decide whether the two triangular intersection. In this paper, using the vector test because of it has more speed advantage. Finally, seek out the intersection and the remaining triangular merger into a new mesh.In this paper, but at present, to achieve a simple merger of the terrain, can be added after the integration of other objects such as housing, roads, facilities, but it also can add terrain evolution of the hardware can be further using to speed up the merger process.