Research On Digital Elevation Model Considering Terraced Terrains

Digital Elevation Model (DEM) is the most important basic geographic data used to represent landform characteristics at present. The multi-scale natural landforms can be represented digitally by the multiscale grid-based DEMs in the basic geographic databases in our country. Because these grid-based DEMs are natural landforms-oriented, the artificial landforms on the natural landforms are relatively less considered. Therefore, there are relatively serious landforms distortions while the natural-artificial landforms are represented with the traditional grid-based DEMs, which makes the effective digital representation of the compound landforms difficult and makes the results of terrain analysis inaccurate. Thence, the wide use of traditional grid-based DEMs are restricted, which is commonly accepted to be the most pressing matter to be solved not only in research, but also in the constructions. No doubt, it also becomes the important problems to be solved in the theory and methods of GIS.Although natural-artificial compound landforms have many types, there also exist some common characteristics. Taking the area of loess plateau in north of Shanxi province as example, there are typical natural-artificial compound landforms because that the water and soil conservation has been strengthen and many slope projects and valley projects of water and soil conservation have been constructed in small watershed in recent years. Seen from the common characteristics of landforms, natural-artificial compound landforms have three main characteristics, namely "succession, regularity and changeability". They mean the succession of shape of original landforms, regularity of surface characteristics and the changeability along with the change of type of land use respectively. These characteristics bring many difficulties to the digital representation and analysis of natural-artificial compound landforms. Terraces are the most typical natural-artificial compound landforms, and become the most important method of water and soil conservation for their large scale distribution and good effect of water and soil conservation in loess plateau area. Therefore, aiming at "succession, regularity and changeability" of terraces, this paper takes the terraces as examples, and puts forth a new DEM (terrace DEM--T-DEM for short) that is based on Grid-TIN hybrid mesh and object-oriented thought and can give consideration to terraces landforms fully. The basic theory and methods of T-DEM, such as the conception and main characteristics, data organization forms, key constructing technologies and application methods about T-DEM, have been studied.The main research results are as follow:1. Presenting scientific concept and expounding their scientific meaning of T-DEM. The main characteristics, classification system, relationship with the traditional DEM of T-DEM have been studied, and the basic theoretical framework of T-DEM has been established initially.2. Presenting the T-DEM-oriented elevation sampling points, feature points and feature lines classification system and TIN-based sampling method.3. Based on Grid-TIN hybrid mesh and object-oriented technology, the object-oriented T-DEM model that is based on global Grid, local SubTIN and local terrace objects is put forth. The main key technologies, such as "local SubTIN embedding into global Grid", "two-stage indexes", have been broken through basically. The basic methods of digital terrain analysis of T-DEM and the visualization of terraces have also been realized.4. Based on different tactics, the construction of digital analogue models of terraces has been realized. The 3D visualization of terraces and primary applications about terraces’shape description, digital terrain analysis and applications of water and soil conservation about LS factors have also been realized.This study perfects and extends the basic theory and methods architecture of traditional DEM, which also has important application prospects for overcoming of many problems in the digital loess plateau construction of ecological and environmental information.