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Wieloskalowe modelowanie rzeźby terenu. Cz. 2

Kochman M., Olszewski R.

Polski Przegląd Kartograficzny

2005

T. 37, nr 4

267-273

W drugiej części artykułu omówiono wybrane koncepcje generalizacji numerycznego modelu rzeźby terenu, ze szczególnym uwzględnieniem metody wagowanej filtracji lokalnej opartej na uogólnieniu linii strukturalnych. Zaproponowano także koncepcję budowy wieloskalowego NMT o strukturze hierarchicznej, umożliwiającą monoskalową reprezentację modelu rzeźby na określonym poziomie uogólnienia.

The concept of hierarchical model of relief is a logical conclusion of the idea of a multi representation topographic database. It permits a combined analysis of all the components of the environment and uncovers new possibilities in preserving the integrity of spatial constraints between the model of terrain and other thematic layers (primarily river network). It is possible due to, among other factors, defining of spatial relations between particular objects and object classes. It also provides a new way of looking at the process of relief generalization understood as an approximation of the relief model preserving topological relations, and not as a simplification of contour lines. The basic feature of the generalization of relief should be the preservation of its structure (morphological skeleton). What seems important for the construction of multi scale DTM is not only a hierarchical approach to relief modelling but also the method of approximation of source data. Simple algorithms of DTM generalization such as the conversion of TIN model into regular GRID structure of certain spatial resolution and the application of global filtration allow for a relatively low reduction of complexity of the source model. The proposed concept of hierarchical model preparation through iterative elimination of points from the data source combines elements of local filtration and heuristic approach. In the conducted research it was assumed, that while building the hierarchical structure of DTM model one should define relief structural lines and assign to them appropriate numeric weights. The analysis bases on the division of source data of the model into structural and mass points. In the process of generalization the points are removed according to the combined evaluation of several criteria: their vertical significance (established locally), their density (horizontal significance), and for structural points also by the weight of structural lines and local curvature of those line (established horizontally as well as vertically). The selection of relevance of particular criteria is fully parameterized, permitting a free assignment of weight factors. Hierarchical (multi scale) model of relief can be adapted to the scale of presentation chosen by the user, while retaining the relief structure relevant for that level of generalization. Suggested algorithms make it possible to preserve significant topological relations between structural elements of relief.