Digital Terrain Model Data Structures

This paper describes pertinent digital terrain model data structures, namely, grid/raster, quadtree, and triangular irregular network. A basic concept of DIM data structure is also explained. The aspects of TIN storage, TIN data structure conversion, advantages and disadvantages of each structure are discussed. A complete data structure conversion program is also presented. n. 1.0 INTRODUCTION Digital Terrain Model (DIM) is used to represent the earth surface or part of the Ir, surface digitally. Historically, DTM was introduced by engineers at Massachussetts Institute of Technology (MIT) in the late 1950's. Their definition of DTM is: "digital terrain model (DIM) is simply a statistical representation of continous surface of the ground by a large number of selected points with known x,y,z coordinates in an arbitrary coordinates field" (Kennie and Petrie,(1990)). The definition was based on the nature of the work at that point in time i.e. engineering. Today several terms begin to manifest and can be recognized as Digital Elevation Model (DEM), Digital Height Model (DHM), Digital Ground Model (DGM), Digital Terrain Model (DTM), and Digital Terrain Elevation Data (DTED). Dispite of the differing terms have been used all of them represent the same phenomena i.e. the topography of the earth surface. 2.0 DATA AND STRUCTURES The pattern of DTM data could be regular or irregular. The regular may be in the form of square or rectangular grid while the irregular one may be based on triangular network of irregular size, shape and orientation. These DIM data could be structured in different ways such as grid/raster, quadtree, and triangular irregular data structure. Mark(1978) defined data structure as a collection of facts or data together with their relations. In DTM, data structure is a way of organizing the XYZ coordinates (e.g. in table form) in such a way that the data can be processed and manipulated efficiently. To make a process more efficient then a data structure may be restructured to another format. One should bare in mind that computer system, programming language, nature of the problem to be solved, nature of the data, and