Research Of Three-dimension Raster Data Creation And Section Display Algorithm

In the research of the three-dimensional Geographic Information System (GIS), three-dimensional data model and data structure is the core. The three-dimensional spatial data model includes the raster data and the vector data according to the data description format. As a result of spatial objects can be rendered by the discrete raster values, raster data structure has more advantages in showing inner characters of spatial object. It has higher efficiency in heterogeneous character and some spatial analysis. So it is one of important basis for spatial information system. The algorithm of three-dimensional raster data creation and the algorithm of section display for raster data model are mostly researched in the thesis.A modified inverse-distance weighting (IDW) algorithm is proposed in the thesis, which generates the raster data corresponding to the real situation. This algorithm firstly makes the discrete points pre-processed, and secondly experimental variation function is used to estimate the correlation length of the data. The search method implemented in the paper searches all eight neighboring octants of raster-node. In the octant-search method, for every octant, all data-points are sorted based on the Euclidian distance of the known point to the estimated point, finally a selected number of data-points, starting with the closest ones, is used to compute by the ordinary IDW interpolation algorithm. In the algorithm, experimental variation function can reduce the search distance effectively and the octant-search approach can decrease the cluster effects.Concerning the research of the section display algorithm for raster data model, a section display algorithm of searching out all the raster units which intersect the section accurately is presented in the thesis. The intersection of an arbitrary plane and some raster is realized in the algorithm. The algorithm firstly gets the outermost raster units of intersecting with the section by calculating, and secondly projects the section to the xz plane according to y value order by order. Finally, all the raster units of intersecting with the section are obtained according to the mathematical relationship. The algorithm reduces the amount of calculation in judging whether the raster units intersect the section, and it is used very well in visualization in scientific computing.