Đại diện Multi-Quy mô của mô hình địa hình kỹ thuật số Hai chương trước đã đề cập đến các vấn đề về chất lượng của DTMs. Cơ quan đại diện của dữ liệu DTM sẽ được thảo luận trong chương kế tiếp. Chương này sẽ xem xét một số vấn đề đại diện theo nhiều quy mô. 9,1 MULTI-QUY MÔ ĐẠI DIỆN CỦA DTM: TỔNG QUAN Trước khi đại diện theo nhiều quy mô của dữ liệu DTM có thể được thảo luận, nó là điều cần thiết để làm rõ một số khái niệm liên quan đến quy mô, để hiểu những. | CHAPTER 9 Multi-Scale Representations of Digital Terrain Models The previous two chapters addressed the issues on the quality of DTMs. The representations of DTM data will be discussed in the next three chapters. This chapter will look at some issues on multi-scale representation. MULTI-SCALE REPRESENTATIONS OF DTM AN OVERVIEW Before multi-scale representations of DTM data can be discussed it is essential to clarify some concepts related to scale to understand what is to be addressed in this chapter. Scale as an Important Issue in Digital Terrain Modeling Scale is a confusing concept often misunderstood and meaning different things depending on the context and disciplinary perspective Quattrochi and Goodchild 1997 p. 395 . Scale is an old issue in geosciences such as cartography and geography. In cartography maps are produced at different scales for example 1 10 000 and 1 100 000. A ground area with a fixed size will be mapped into a bigger map space at a larger scale. For example a ground area of 10 km X 10 km will be a map area of 1 m X 1 m at a scale of 1 10 000. However at 1 100 000 it is an area of only m X m on map. Due to the reduction in size from 1m X 1 m to m X m the same level of detail LOD as represented on the larger-scale map cannot be represented on the smaller-scale map. This means that the representations of the same feature in the same area will be different when the maps are at different scales. Therefore there is a multi-scale issue in cartography that is how to derive small-scale maps from large-scale maps through operations such as simplification and aggregation. This issue is called generalization. 191 2005 by CRC Press 192 DIGITAL TERRAIN MODELING PRINCIPLES AND METHODOLOGY In geography there is a similar issue. Normally geographical data are sampled from enumeration units. The size of the enumeration unit is a scale indicator. In some geographical applications a larger unit is needed as the basis for analysis. The
