DIGITAL TERRAIN MODEL AS A COMPONENT OF THE MRDB TYPE REFERENCE DATABASE IN POLAND
D. Gotlib1, R. Olszewski1, T. Berezowski2
1 - Institute of Photogrammetry and Cartography, Warsaw University of Technology, Poland
2 - Intergraph - Polska
Conceptual models of topographic databases, which have been developed, utilise the concept of „multi-resolution” and „multi-scale” databases (MRDB). Such an approach allows to model topographic objects of various levels of generalisation and geometric accuracy in one spatial database, which is coherent from the conceptual point of view. However, the existing works are mainly focused on „multi-scale” or „multi-resolution” modelling of the 2D vector topographical database. Development and implementation of such methodology for the needs of modelling of the terrain relief would allow to implement a coherent concept of the 3D multi-resolution DTM. This approach allows to develop the digital terrain model for two or more levels of generalisation in such a way that it will be possible to operate the data as one model. This also opens wide possibilities to maintain the spatial integrity between the model of the terrain relief and topographic and other feature classes (first of all the river network).
Several works concerning acquisition of digital elevation data, such as the digital terrain model in the TIN and/or GRID formats, as well as contour lines, have been recently developed in Poland. For the needs of NSDI development, and, in particular, for development of the concept of the multi-representation reference database, the most important is the basic elevation data – survey data and the irregular TIN model, which maintains the important topological relations. Data in these forms are stored in three databases:
§ In the Topographic Database (which, at present, covers about 5% of the area of Poland, the digital terrain model (ms = 1m) has been developed as a separate component).
§ In the LPIS (Land Parcels Identification System) Database, with utilisation of aerial photographs – the digital terrain model is being developed for the entire country (ms = 1,5m)
§ For considerable areas of the southern Poland (about 11% of the area of Poland) the high quality digital terrain model (ms = 0,8m) has been developed within the frames of development of the SMOK (Flood Protection Systems).
At present those databases are not harmonised and there is no data flow between them. Within the research and implementation Project No. 6 T 12 2005C/06552 “Methods and procedures of integration, visualization, generalization and standardization of state geodetic and cartographic resources databases and their usage in creating thematic databases” the authors made attempts to develop the concept of a coherent multi-resolution reference database, the important element of which are elevation data integrated with the TOPO module. Modification of the existing concept of the DTM component of the TBD Database, separated from vector data, is, first of all, to achieve a more coherent terrain model, which considers topographic elements and the terrain relief in a similar way, as well as to maintain important topological relations between particular classes of objects.
The authors propose to develop the digital terrain model according to the following assumptions:
· Creation and transfer of elevation data to the multi-resolution TBD Database as the spatialy “continuous” database, similar to vector data included in the TBD. Data should be transferred to the TBD Database in the form of survey data only (source data). Other forms of elevation data, such as TIN, GRID or derivative contour models should be independently processed by the recipients of the TBD, basing on user defined parameters,
· Making the conceptual model of TBD vector database and DTM components coherent and defining and maintaining topological relations between particular objects and classes of objects,
· Utilisation of elevation data stored within the TBD, LPIS and SMOK Projects for creation of two (or more) levels of the DTM component of the multi-representation reference database,
· In the process of data acquisition for the DTM, area division into regions of diversified terrain relief characteristics should be considered. Depending on the region, different data collection parameters should be used,
· Development of elevation data generalisation algorithms, which maintain the defined topological relations between topographic and elevation elements, modelled in the spatial database,
· Considering characteristic elements of the terrain as features, which represent selected real object, such as: mountain peaks, chains, saddles, valleys and ravines. Storing additional information in the form of attributes, together with objects, which represent the terrain relief, allows to record a series of names of objects, which have occurred on topographic maps and which are important for the TBD Database users.
The approach proposed above also allows to apply the same standards of recording and data exchange for the TBD vector database and DTM components, as for example the GML language. Besides, this approach allows to increase the level of coherence of the topographic database structure. It also opens wider possibilities in the field of maintaining the spatial integrity between the terrain relief model and terrain objects (first of all, the hydrographic network). This will allow to develop the complex model of generalisation of the terrain relief, which is understood as maintenance of topological relations of the terrain relief model and not simplification of contour drawings.
§ Bac-Bronowicz J.,Gotlib D., Olszewski R., Synchronizacja różnych rejestrów danych w ramach koncepcji wielorozdzielczej bazy danych topograficznych dla Polski, Synchronisation of variuos registers of data within the concept of a multi-resolution topographic database for Poland, ICA Conference, Moskwa, 2007
§ Gotlib D., Olszewski R., Możliwość wymiany danych między bazą SITop a bazami VMap, w: A. Makowski (red.), System informacji topograficznej kraju. Teoretyczne i metodyczne opracowanie koncepcyjne, Possibilities to exchange data between the SITop and VMap databases, A National Topographic Information System, Oficyna Wydawnicza Politechniki Warszawskiej, Warszawa, 2005
§ Gotlib D., Iwaniak A., Olszewski R., SDI in
Poland – concept of topographic reference system for thematic, harmonized
databases, ICA Conference,
§ Gotlib D., Iwaniak A., Olszewski R., Budowa krajowej infrastruktury danych przestrzennych w Polsce – harmonizacja baz danych referencyjnych, Development of the National Spatial Data Infrastructure in Poland – harmonisation of reference databases, Wydawnictwo AR, Wrocław, 2006