Próba automatyzacji procesu generalizacji wybranych elementów Bazy Danych Ogólnogeograficznych
Wybrane pełne teksty z tego czasopisma
An attempt to automate the generalization process of selected components of general geographic database
One of the main assumptions of an automatic generalization is understanding of the process taking into account its formalization. Such an approach is based on a proposal of performing elementary steps in computer GIS environment in order to obtain generalized spatial data at particular detail level. However, it should be expected that the generalization steps are so objective that when carried out by two cartographers independently they bring common result. As the National Geographic Information System and its components are developed in Poland (its components include: Topographic Database at 1:10 000 scale, Vector Map Level 2 at 1:50 000 scale, General Geographic Database at 1:250 000 scale), topicality of he generalization grows ever larger. Under such conditions there is a need for creating a uniform spatial database out of which maps AT various scales and for various purposes could be generated. The executed project is extremely important from the point of view of building spatial data infrastructure in our country. Having joined the INSPIRE initiative, Poland is required to provide the information society with well-understood spatial data collected at different resolution levels. However, the purpose of the project is to define and then to assign a particular portion of information to a particular resolution level and, consequently, to work out a methodology of generalization of the basic spatial database GGD. The scope of the study covered carrying out generalization experiment concerning the generalization of thematic layers . transportation network and settlement for the area of the Lower Silesia Province. This study was a continuation of previous works concerning generalization possibilities of spatial databases (I. Chybicka, A. Iwaniak, W. Ostrowski, 2004). The intention was to elaborate a multi resolution/representation database as visualization of the General Geographic Database (GGD) at different resolution levels without permanent loss of information. The selection of information depends not on durable data withdrawal from a database but only on visualization of the generalized information adequately to resolution level. The visualization of the GGD was performed based on three levels: 1:500 000, 1:1000 000 and 1:4000 000. The operations forming the generalization process may be classified in different ways. The autor agrees with the concept of dividing the process into the data model generalization and the cartographic generalization proposed by M. Bell, D. Neuffer, P. Woodsford (2004). The data model generalization makes it possible to reduce the number of data in relation to the assumed resolution level. It covers the following actions selection of whole feature classes, selection of object components from a particular feature class on the basis of attributes and spatial conditions, change of object.s geometry type (way of presentation and method of object.s presentation), geometry simplification. The role of the cartographic generalization as a stage following the data model generalization is to obtain optimal map legibility at a given scale. The cartographic generalization process consists of: application of proper data symbology, shifting of objects; aggregation; changing of object.s dimensions. The author focused on the first stage of the generalization process (connected with the data model generalization). The selection of the map content for visualization on particular resolution degrees was performed on the basis of analysis of existing geographic maps as well as interviews with experts in the field of generalization. Ordering the map content to the visualization performed for each of the 34 Izabela Chybicka scales (1: 500 000, 1: 1000 000, 1: 4000 000) covered performing proper spatial and attribute analyses in the GeoMedia system. The operations connected with the simplification and objects. smoothing were performed in the DynaGEN application. This process encompassed simplification of routes and their smoothing as well as simplification and smoothing of buildings' contours.
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