A Digital Elevation Model is a bare-earth raster grid referenced to a vertical datum. The DEM can even be obtained from stereo digital aerial imagery at various resolutions, depending on the quality and scale of the imagery. 1. Ground Survey Techniques: Ground Survey Techniques are the most widely used, in this technique we have to collect points through a ground survey. Previously this technique was used but it covers fewer areas. This is the accurate surveying of point locations. By exploring the known areas of XYZ, neighboring areas are measured using a device called a theodolite. This requires highly skilled workers, and like DGPS, all points need to be translated to produce a continuous raster.
