Research And Implementation Of Contour Map Generation Algorithm Based On Discrete Points

With the development of computer hardware and software technology, since the50’s of the last century, digital elevation model algorithm has been one of the research areas to learn the classic, after continuous efforts of many scholars, grid, triangulated irregular network model, contour model and a series of mature models emerge as the times require, in the theoretical model, also produced some of the more mature thought. Many digital elevation model (DEM), to the more commonly used TIN algorithm, so the generated has attracted a lot of attention.Firstly, the traditional algorithm to generate triangulated irregular network based on DTIN tracing isoclines generation principle are summarized, the main features of the analysis, combined with traditional methods to study the whole process. Algorithm generally involves four aspects:the establishment of triangulated irregular network is divided into discrete points of triangle (D-TIN), in the form of contour point set based on D-TIN, opening and closing two contour drawing, contour smooth and moderate labeling. The process of discrete point mesh generation D-TIN, compared with the traditional method, using an algorithm of triangulation growth relatively practical, it generates a triangulation algorithm based on growth, the nearest point algorithm to reduce the number of search, reduces the computational complexity are the two main directions of improvement the growth, expansion algorithm is the content of the polygon, not triangles, but only two of each triangle, triangle edges extend, rather than the three sides; in the baseline judgment based on the nearest neighbor, refinement, the discrete points in the baseline (directed line segment) as the boundary is divided into left and right the two point sets (fell discrete points in line with the baseline cannot constitute a triangle, so do not consider), using the point of need of judgment, reduce the degree of the nearest point number of judgment, only by judging whether the maximum angle, don’t judge whether is located on the left (right), above is the improvement of the general algorithm. It is worth mentioning that in the design of D-TIN data structure, absorbing the traditional data structure provided by ArcEngine, PointClass, LineClass two class based supplement some new attributes, respectively corresponding to CoordinatePoint, Edge, custom Triangle class, the new structure of the storage point, edge line, more conducive to the calculation of equivalent points and the subsequent contour tracking. The traditional contour tracing process is separated from the contour and closed contour are calculated in this paper, the equivalence point and contour tracking mode for a new attempt, firstly, the calculation of equivalent points, the results will be stored into a collection, then analytic equivalence point set, at the same time opening and closing contour tracing (contour provided by ArcEngine the PolylineClass class object rendering). Using Smooth function of PolylineClass contour lines on smooth, this method is simple and quick, fold line can be set according to the corresponding component contour parameters into the Bessel curve is relatively smooth. Finally, for the use of ArcEngine to tag the contour layer.After the test, a practical algorithm of discrete points generation D-TIN to some extent improve the speed, and has a strong practical; also validate the new tracking mode, the results are reliable.