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introduction_definitions_and_data_structure_dem
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Table of Contents
Types of objects
- Continuous fields
- elevation, rainfall
- represented by raster data model
- Discrete objects / features
- lines, points, areas with attributes
- represented by vector data model as geometry with attribute table or object based
- can be also represented by raster data model (streams, roads, landuse??? - we have vector, but whatever)
DEM
- is a digital model or 3D representation of a terrain's surface created from terrain elevation data
- DEM can be represented as a raster (a grid of squares, also known as a heightmap when representing elevation) or as a vector-based triangular irregular network (TIN). The TIN DEM dataset is also referred to as a primary (measured) DEM, whereas the Raster DEM is referred to as a secondary (computed) DEM.[9] The DEM could be acquired through techniques such as photogrammetry, lidar, IfSAR, land surveying, etc.
- The values X, Y are referred to a coordinate system, usually a cartographic projection system
the most important elements
- contour lines
- VIPs (very important points)or singular points
- top of peaks
- bottoms or shinkholes
- structural lines
- define linear elements with altitude values associated to each vertex
- network of ridges, streams
- breaklines
- edges of cliffs
- areas of constant altitude
- lake
- clipping zones
- area what defines the outer limits of DEM
- empty areas, without heigh information
- data error, snow
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