Creation ofDigital Elevation Model (DEM)

For the accurate removal of the image distortions, a digital elevation model (DEM) is used to make image orthorectification. The requisite DEM can be produced by semi-automatic DEM extraction software from stereo satellite scenes obtained by the QuickBird, IKONOS, SPOT-5, or ASTER satellite sensors, and stereo aerial photography.

In situations where higher mapping accuracy standards are required, the DEM is extracted from the already existing topographic maps with reference to a standard scale or collected using stereo satellite image data.

To obtain this accuracy standard, adequate GPS-derived ground control points (GCPs) are necessary. Other remote sensing techniques can also be used such as radar interferometry or LIDAR.

When a particular vector data needs to be extracted from satellite or aerial image data by raster-to-vector translation, the process of ortho rectification of the remotely sensed image data can rectify all digital images of geological, environmental, topographic or any other source map which will be used in the GIS mapping environment.

Common uses of DEMs

Extracting terrain parameters,Modeling water flow or mass movement (for example avalanches and landslides),Creation of relief maps,Rendering of 3D visualizations,3d flight planning,Creation of physical models (including raised-relief maps),Rectification of aerial photography or satellite imagery, Reduction (terrain correction) of gravity measurements (gravimetry, physical geodesy), Terrain analyses in geomorphology and physical geography, geographic information system(GIS), Engineering and infrastructure design, Global positioning systems (GPS), Line-of-sight analysis, Base mapping, Flight simulation, Precision farming and forestry, surface analysis, Intelligent transportation systems (ITS).

Reference: Wikipedia