Senų topografinių žemėlapių reljefo naudojimas skaitmeninio topografinio žemėlapio M1:10000 reljefui sudaryti

Abstract

In this article, an analysis of ways for creating DEM (Digital Elevation Model) for digital topographical maps at scale 1:10,000 is made. We can use stereophotogrammetric method, digitising countour lines from old topographical maps or digital ortophotogrammetric method. One of the optimal ways is to use relief from old topographical maps, because to produce a new relief is too expensive for Lithuania today. Now Lithuania is getting back printed originals from abroad, and this will facilitate the solution of the problem. It will be possible to use automatic vectorisation of scanned contour lines. In this way we pass from the linear form of model description to the matrix form. Before using old topographical maps for creating DEM, we need to know the reliability and accuracy of this old material. The largest part of these maps were published in 1971- 85, and now they are about 10-25 years old. Only a small part of maps ( 7%) is less than 5 years old (Fig 1). In the schemes (Fig 2), the intervals of contour lines on topographical 1:10,000-scale maps for all the territory of Lithuania are shown. The maps are in two co-ordinate systems - 1942 and 1963. The intervals of contour lines are 1 m, 2 m, 2.5 m and 5 m. The interval of 1 m shown on maps for 63% of the Lithuanian territory, and intervals 2.5 m and 5 m only for 1%. On some map sheets, the contour line intervals are composite with sometimes even three different intervals. Relief is transformed from old co-ordinate systems to new co-ordinate system LKS-94 for the creating DEM. Methods of compilation of relief as well as the reliability of this material are also analysed. The possibility to use relief from larger scale topographical plans, at 1:5000 and 1:2000, is described. The use of this material is recommended only for some areas.