tailieunhanh - Digital Terrain Modeling: Principles and Methodology - Chapter 2

Mô tả địa hình và chiến lược lấy mẫu Để mô hình một phần của bề mặt địa hình, lần đầu tiên một tập hợp các điểm dữ liệu cần phải được mua lại từ bề mặt. Thật vậy, thu thập dữ liệu là giai đoạn chính (và có lẽ quan trọng nhất) trong mô hình địa hình kỹ thuật số. Đối với điều này, hai giai đoạn được phân biệt, đó là, lấy mẫu và đo lường. Lấy mẫu liên quan đến việc lựa chọn vị trí trong khi đo đạc xác định tọa độ của vị trí. Lấy mẫu. | CHAPTER 2 Terrain Descriptors and Sampling Strategies To model a piece of terrain surface first a set of data points needs to be acquired from the surface. Indeed data acquisition is the primary and perhaps the single most important stage in digital terrain modeling. For this two stages are distinguished that is sampling and measurement. Sampling refers to the selection of the location while measurement determines the coordinates of the location. Sampling will be discussed in this chapter while measurement methods will be discussed in the next chapter. Three important issues related to acquired DTM source or raw data are density accuracy and distribution. The accuracy is related to measurements. The optimum density and distribution are closely related to the characteristics of the terrain surface. For example if a terrain is a plane then three points on any location will be sufficient. This is not a realistic assumption and therefore an analysis of the terrain surface precedes the discussion of sampling strategies in this chapter. GENERAL QUALITATIVE TERRAIN DESCRIPTORS In general two basic types of descriptors may be distinguished 1. qualitative descriptors which are expressed in general terms so that they are referred to as general descriptors 2. quantitative descriptors which are those specified by numeric descriptors. In this section a brief discussion of general descriptors is given and numeric descriptors are described in the next section. As discussed in Chapter 1 different groups of people are concerned with different attributes of the terrain surface. Therefore a variety of general descriptors can be found based on these different interests. However some of them are irrelevant to the concern of digital terrain modeling. Indeed those that indicate the roughness and the coverage of terrain surface are more 13 2005 by CRC Press 14 DIGITAL TERRAIN MODELING PRINCIPLES AND METHODOLOGY important in the context of terrain surface modeling. The following are .