Often, digital data acquired from satellites are collected in a gridded fashion. The DEM type decision depends on the analysis of interestĭigital vector topography can clearly define boundaries, such as valley floors or ridge lines. Choosing to represent digital topography in either vector or raster (TIN or DEM) format depends on the type of GIS analysis a user wants to perform. Raster format divides the topographic surface into equally spaced intervals or a gridded array and then displays the elevation value for each grid cell (called a digital elevation model or DEM).
Digital terrain model vs digital elevation model series#
Vector format uses a series of irregularly spaced elevation points connected by lines into a triangulated irregular network (TIN). Digital topography can be represented in either vector or raster format. In the next blog, I discuss the main technologies used to create DEMs and the pros and cons of each.The recent explosion of Geographic Information System (GIS) tools enable geoscientists to visualize the Earth's surface in three dimensions using digital topography. (It should also be noted the term ‘resolution’ is often applied to DEMs and used interchangeably with ‘density’.) Raster DEMs are characterized by grid cell size, for example, 1 m or 5 m cell size, while vector DEM products are identified by the point spacing or distance between points, i.e., 1 meter, 5 meter, etc. In much the same way that remotely sensed imagery is rated by spatial resolution, DEMs are defined by density of elevation measurements. It should be noted that horizontal and vertical accuracies for one data set are often different. Similarly, vertical accuracy is measured in either z RMSE or by Linear Error (LE).įor example, 1 m CE90 and 5 m LE90 mean there is a 90 percent confidence the DEM measurement coordinates are correct to within 1 and 5 meters, respectively, of their actual locations on the ground. Horizontal accuracy is usually described by either x, y RMSE or Circular Error (CE). DSMs, on the other hand, are utilized in 3D visualization, infrastructure management, line-of-sight, and obstruction mapping applications where knowing the height of any feature, manmade or natural, is critical for success.ĭTMs and DSMs are typically defined by accuracy and grid cell density (or spatial resolution). Generally speaking, DTMs are used in engineering, construction, and hydrographic projects where the topography of the natural terrain is most important. The DSM, on the other hand, contains all elevations whether from the ground surface, vegetation, or manmade structures.īecause DTMs and DSMs contain different information, their end use applications vary greatly and will be covered in depth in the third blog of this series. Vegetation and building features have been digitally stripped from the DTM data set. The DTM is often called a bare-earth or ground-only elevation model because it includes x, y, z values only for the ground. There are two types of DEMs – Digital Terrain Models (DTMs) and Digital Surface Models (DSMs). What are DEMs?Ī DEM data set defines points or grid cells with three values, or coordinates, – x, y and z - where x and y are traditional latitude-longitude location references, and z represents the elevation or height of the point or cell. This series of blogs will help you understand the differences in DEM products and capture technologies, as well as the relative advantages and disadvantages each delivers to specific end use applications. Selecting the right DEM for your application can be confusing because there are so many elevation products available, and they are generated from several data collection and processing technologies. In addition, we can process new customized DEMs or derive 3D information to meet your application needs. The applications of DEMs are diverse, and Harris Geospatial Solutions offers a wide variety of DEMs from multiple commercial sources through our online DataStore.
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