Research Of Isoline Generation And Clipping Algorithm Based On Grid Model

The isoline map, which has been widely used in lots of fields, can display the three-dimensional information on the two-dimensional plane and grasp the characteristics of the object on the whole. This paper mainly discusses the drawing process of the isoline map. Firstly, it introduces the way of data acquisition and representation of the digital elevation model and how to build grid model. Secondly, it tells the generation process of isoline which is based on the grid model. Finally, it describes how to deal with the isoline map, including clipping, smooth and label. Throughout the drawing process, this paper mainly studies the generation algorithm of the isoline which is based on the grid and the clipping algorithm of arbitrary polygon.In the generation algorithm of isoline, this paper improves the original isoline propagation algorithm. First, we can acquire the grid which have equivalent points and set up grid tables. In these grid tables, we need to find the border of grid which have equivalent point and set up border tables. We can use the data of border tables to track the isoline more quickly and determine whether the tracking is ended or not, so it improves the efficiency.In the clipping algorithm of arbitrary polygon, this paper implements an algorithm based on scan strips. In this improved algorithm, we note the different values of clipping polygon vertexes and the equivalent points. We can construct scan strips in the adjacent values and deal with the lines which are in the scan strips, so we get the isoline which is located in the clipping polygon. We used lots of data to test this algorithm and the result proved this algorithm is feasible and effective.At last, this paper implements the function of isoline smooth and label, so the isoline map is more convenient for understanding.