A Seamless and Adaptive LOD Model of the Global Terrain Based on the QTM
In this paper, a new seamless and adaptive LOD (Level of Details) modelling method of global terrain based on the QTM (Quaternary Triangular Mesh) is described. Our approach starts with QTM tessellation based on the WGS84 ellipsoidal surface. Thus, the gl
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Abstract In this paper, a new seamless and adaptive LOD (Level of Details) modelling method of global terrain based on the QTM (Quaternary Triangular Mesh) is described. Our approach starts with QTM tessellation based on the WGS84 ellipsoidal surface. Thus, the global terrain can be represented by an array of elevation values of QTM vertices. Next, an adaptive idea of a Binary Triangle Tree is inserted in this QTM model to form an adaptive, continuous, and uniform LOD triangular mesh in the DEM grids and their vertices completely coincide with the vertices of QTM. The experiment and analysis are carried out with the global terrain data, GTOPO30. The results illustrate that: (1) the global DEM model based on QTM is seamless, hierarchical, and regular over the whole Earth, and the dataset occupies only about half of its initial size; (2) an adaptive LOD (Level of Details) model of the DEM data blocks is constructed and the problem of discontinuity in different subdivision levels is overcome; and (3) the number of the triangles in this adaptive LOD model decreases greatly as their error tolerances increase, but there is no obvious change in the results. Keywords: global terrain, QTM, adaptive partition, LOD.
1 Introduction The representation of the physical surface of the Earth in digital systems is a subject of considerable current attention. As the area of coverage of such systems increases, it becomes necessary to provide methods to model very large, continuous surface conglomerates in a manner that does not violate surface integrity. The regular or irregular Digital Elevation Model (DEM) grids based on the idea of map projections are effective traditional methods for modelling the terrain on the local or small-scale spherical surfaces as a flat surface, and many corresponding algorithms have been presented over the last decade (Lindstrom et al. 1996, Lindstrom and Pascucci 2002,
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ZHAO Xuesheng, BAI Jianjun and CHEN Jun
Duchaineau et al. 1997, Kolar 2004). However, a spherical surface is not topologically equivalent to planar Euclidean space in geometry. Although the traditional DEM grid may support an individual project or small area terrain visualization modelling, they do have some significant drawbacks for modelling large areas or the whole Earth surface, such as geometric distortions, data discontinuity, space inefficiency, and difficulties with data sharing between projects caused by a lack of good global representation schemes (Lukatela 2000). The Quaternary Triangular Mesh (QTM), first proposed by Dutton (1989), is a tessellation of the Earth’s surface with non-overlapping (or broken) triangular cells. In QTM partition, an octahedron is used as a basis. It can be readily aligned with the conventional geographic grid consisting of longitude and latitude. When this is done, QTM vertices occupy cardinal points and their edges assume cardinal directions, following the equator, the prime meridian, and the 90th, 180th and 270th meridians, making it simple to determine in which facet a point on the planet i
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