Mapping of vector and DEM is one of main methods for ascertaining spatial object locations in 3D dimension space. What's more, mapping technology has been widely used in the analysis and management of virtual landscape. Various methods of mapping vector data and DEM on the plane have been approached. However, when those methods are used for mapping global-scale vector data set and DEM model, they do have some significant drawbacks, such as improper matching in geometry-based mapping, heavy texture distortion in texture-based mapping etc. To overcome these deficiencies, a new geometry-based method based on hierarchical Longitude/Latitude Grid, which is the simplest and most useful one of global discrete grids, is developed in this paper. Our approaches start with dividing longitude/latitude grids on the spherical surface hierarchically. Then, constructing global DEM model base on this structure is presented in brief. Next, the detailed geometry-based mapping algorithm is introduced. In the end, the experiment is made to test the algorithms and methods by using GTOPO30 and Chinese county boundary data. The result indicates: the methods and algorithms discussed in this paper are feasibility and effective.Keywords: vector and DEM mapping, Geometry-based mapping; Longitude-Latitude Grids;
I. INTROUDCTIONVector usually consists of points, lines, polygons and is used to describe the positions and attributes of spatial objects, such as road networks, buildings, vegetation and soil types etc [Schneider and Klein 2007]. And topography of the terrain can also be represented by contours, which are also vectors and are digitized and converted into grid digital elevation model (height map). Although to understand spatial information of vectors is very easy for cartographers and survey engineers, to acquire all accurate information of vectors still is a difficult task for common users because vector is approached by projecting the real threedimensional world onto a two-dimensional plane. Therefore, it is necessary to render vector in three-dimension because mapping vector data and DEM model provides information on geographical data about the shape of the terrain and location of other objects on a vector map quickly and easily. On the plane, various methods of mapping vector data and DEM have been approached. They can be classified as texture-based and geometry-based approaches [Dollner 2005; Bruneton and Neyret 2008]. A critical examination of these approaches is as followings.Texture-based Approaches. Texture-based approach is to rasterize the vector data into a texture and use standard texture mapping techniques to project it onto the DEM grid. To improve the speed of producing texture, Dollner et al [2002; 2005] uses P-buffer technology to create texture for rendering vector in three-dimension space. Schneider [2005; 2007] provides an algorithm to render 3D vector data using the theory of stencil shadow volumes. To acquire multi-resolution textures, Bruneton and Neyret [2008] develop a rasterizing vector method base on ...
