| This thesis applied synthetically those theories and technologies of computer graphics, computational geometry and geometrical modeling, scientific computation visualization, interactive, virtual reality, computer animation etc, to research thoroughly and carefully on several critical technology of computer aided alignment design, such as digital terrain model, interactive alignment, 3D modeling of route entity, simplification of 3D model, showing realistic image and dynamic and real time display of 3D route scene etc. By thoroughly analyzing the relation between the 2D horizontal, vertical and cross-section design and the 3D visual design, the conclusion could be reached that both are not substituted mutually (this being advocated and the other being cut down), but are mutually replenishing, and supplementing and complementing each other. They should be combined closely and applied synthetically. Based on this idea, the research work was carried out and closely centered on the theories and methods whose characteristic was combining 2D design with 3D design . Consequently not only the improvement of traditional methods of the 2D horizontal, vertical and cross section design but also the researches and applications of some new technologies such as 3D visualization , virtual reality etc, had been laid stress on in this thesis .The chief research contents and achievements could be summarized as follows:1) Based on the theories of Delaunay triangulation and constrained Delaunay triangulation, the algorithm for fast and integrally creating irregular triangulation net adapted to railway and highway alignment design was put forward and realized. It adopted an integral creating TIN technology which need not divide an enormous sum of topography points into some pieces in advance and could build a whole continuous strip triangle net without seams. Benefit from that, the question of bordering caused by dividing the points into pieces was avoided. The building speed achieved 40000 -45000 triangles per second on normal PII computer, furthermore, the influences of topography characteristic edges were concerned in computation course. The algorithm had such characteristics as the numberof points it once dealt with was limitless, with the whole TIN being continuous without seams, the building speed very high, the net shape top excellent , the precision very high and the use wide etc. It has been verified by its successful applications. Up to now, it has accomplished the design works of near 1000 kilometers highway and more than 2000 kilometers railway .2) In order to eliminate the defects drawn from the preceding route CAD systems into the horizontal design, the vertical design and the cross section design separated, in the thesis a new road design method had been presented for the first time that was to integrate the horizontal plan, the vertical profile map , the cross-section map and the 3D perspective map of the route on the same interface. It realized the alternate design and the interrelated design of the horizontal plan, the vertical profile map and the cross-section map and provided a great deal of information query functions which made the designer give adequate considerations to the other two aspects when being engaged in the one aspect of the three kinds of design. The CAD systems developed on these grounds not only retained the relative independence but also laid more stress on the interrelation among the horizontal design, the vertical design and the cross-section design, therefore were more in accordance with those characteristics of route design.3) The problem of 3D modeling of route entities was solved by the boundary expressing method based on the idea of dividing and conquer. This method divided the complicated route entities into several essential factor sub-entities. The 3D entity modeling method of each sub-entity was worked out respectively to accomplish each modeling, then assembled the various models. The theory of constrained Delaunay triangulation was applied to develop the algorithm of "...
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