Космические снимки, цифровые карты, геоинформационные системы

  Digital Elevation Models

    Lately a lot of GIS-projects are not carried out without the Digital Elevation Models (DEM).

   The tasks which can be solved with the help of DEM are diverse and among them one can single out the following:

·         the calculation of slope ratio and direction of slopes, which is important in the construction of roads and product pipelines, in agriculture, in selecting the fields for the cultures with different requirements to the luminance, etc.;

·         the land runoff analysis of the territory;

·         the water flooding simulation of the territories;

·         the visibility analysis used during the planning of communication networks, in military science and other fields;

·         the ortho-rectification of images;

·         the measurement of areas and volumes, the obtaining of surface profiles;

·         the review of data in three dimensions, the engineering of virtual flights above the terrain and light-and-dark models.

The digital elevation models with different plan and height accuracy are necessary to solve such tasks. The data source for the DEM engineering is the topographic maps, stereo-pairs of aerial and space images, radar survey data, etc. The relief accuracy is influenced by many factors such as, the spatial resolution and geometrical quality of the images, the air condition, the map scale, the accuracy of controlled points, etc.

The mostly widespread methods of the relief digital representation are the raster representation and the special model of spatial data based on the TIN network and approximating the relief with the multisided surface with the altimetric data (depth points) in the junctions of triangular network. On their base can be formed the 3D mapping of the relief surface (Fig. 1).

Fig. 1 The 3D mapping of the relief, engineered on the basis of the raster DEM

Fig.1 Relief 3D reflection created on the base of raster DEM