The tools operate on the assumption that for any single cell, water can flow in from many adjacent cells but out through only one cell. There is an assumption that the surface contains sufficient vertical relief that a flow path can be determined. It includes not only heights and elevations but other geographical elements and natural features such as rivers, ridge lines, etc. The hydrologic analysis tools are designed to model the convergence of flow across a natural terrain surface. A digital terrain model (DTM) can be described as a three dimensional representation of a terrain surface consisting of X, Y, Z coordinates stored in digital form. ABSTRACT: Relief characterization using a digital terrain model (DTM) is widely applied in erosion, soil and vegetation modeling. Again, this is most noticeable on integer data in flat areas. This can increase as much as 5 percent for a 3-arc-second DEM.ĭEMs may also contain noticeable striping artifacts, a result of systematic sampling errors when creating the DEM. It is not uncommon to find 1 percent of the cells in a 30-meter-resolution DEM to be sinks. This can be particularly troublesome in areas of low vertical relief. Another common cause of sinks results from storing the elevation data as an integer number. The number of sinks in a given DEM is normally higher for coarser-resolution DEMs. Learn more about removing or filling sinks.Sinks, being areas of internal drainage, prevent downslope flow routing of water. These are more commonly natural features and are less detrimental to the calculation of flow direction.Įrrors such as these, especially sinks, should be removed before attempting to derive any surface information. Likewise, a spike, or peak, is an area surrounded by cells of lower value. Some of these may be natural, particularly in glacial or karst areas (Mark 1988), although many sinks are imperfections in the DEM. DEMs can be represented as a grid of squares, or as a vector-based triangular irregular network (TIN).
#What is a digital terrain model free
A DEM is a ‘bare-earth’ elevation model, meaning it is free of vegetation, structures, and other non-terrain objects. A sink is an area surrounded by higher elevation values and is also referred to as a depression or pit. A digital elevation model is a three-dimensional, computer-generated representation of a terrain surface. Visualization of a raster DEM surface.Įrrors in DEMs are usually classified as either sinks or peaks. Other factors affecting accuracy are data type (integer or floating point) and the actual sampling of the surface when creating the original DEM. The accuracy of this data is determined primarily by the resolution (the distance between sample points).
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Modern surveying and photogrammetric equipment enable rapid three-dimensional data acquisition. This data is used as input to quantify the characteristics of the land surface.Ī DEM is a raster representation of a continuous surface, usually referencing the surface of the earth. A digital Terrain Model (DTM) is a numerical representation of the configuration of the terrain consisting of a very dense network of points of known X, Y, Z coordinates. The most common digital data of the shape of the earth's surface is cell-based digital elevation models (DEMs).