Terrain Analysis: DEM (Digital Elevation Model) and TIN and Relation between Them (Especially for GATE-Geospatial 2022)

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Surfaces represent a continuous field of z-values with an infinite number of points. Linking height (z-value) as an attribute to each point (x, y) .

GIS contain terrain mapping features that allow it to be used in a variety of applications. Two data formats are used for terrain mapping and analysis:

Diagram Shows Two Types of Terrain Mapping and Analysis

DEM (Digital Elevation Model)

Digital Elevation Models (DEMs) are a type of raster GIS later. Raster GIS represents the world as a regular arrangement of locations.

In a DEM, each cell has a value corresponding to its elevation. The fact that locations are arranged regularly permits the raster GIS to infer many interesting associations among locations:

  • Which cells are upstream from other cells?
  • Which locations are visible from a given point?
  • Where are the steep slopes?

One of the most powerful applications of DEMs is adding synthetic hillshading to maps so that the map reader may see the relationship between terrain and other things you may be mapping.

Digital Elevation Model - Red Rocks Obtained Using an UAV

A DEM represents a regular array of elevation points. Most GIS users in the United States use DEMs from the U. S. Geological Survey (USGS) . Alternative sources for DEMs come from satellite images, radar data, and LiDAR (light detection and ranging) data. Regardless of its origin, a point-based DEM must be converted to raster data before it can be used for terrain mapping and analysis.

The quality of a DEM can influence the accuracy of terrain measures including slope and aspect. The USGS offers a nationwide coverage of elevation data through the National Elevation Dataset (NED) in three resolutions: 1 arc-second (30 meters) , 1/3 arc-second (10-meters) , and 1/9 arc-second (3 meters) .

Based on the root mean square (RMS) error, a statistic used for the National Standard for Spatial Data Accuracy, a recent report from the USGS suggest that the absolute vertical accuracy of NED 1/3 arc-second ranges from 2.03 to 4.66 meters, depending on the production method, with an average of 2.44 meters.

TIN (Triangulated Irregular Network)

Image Shows Creating a Triangulated Irregular Network Model

A triangulated irregular network (TIN) is a digital data structure used in a geographic information system for the representation of a surface. A TIN is a vector-based representation of the physical land surface or sea bottom, made up of irregularly distributed nodes and lines with three dimensional coordinates (x, y and z) that are arranged in a network of nonoverlapping triangles. TINs are often derived from the elevation data of a rasterized digital elevation model (DEM) .

The input data to a TIN come from:

  • DEM
  • Surveyed elevation points, contour lines,
  • Break lines: line features that represent changes of the land surface such as streams, shorelines, ridges, and roads
Figure Shows Dashed Line or Breakline

The dashed line in (b) represents a breakline, which subdivides the triangles in (a) into a series of smaller triangles in (c) .

  • Not every point in DEM is used to create TIN.
  • Selected points are selected using algorithms e. g. , VIP, z-tolerance.

The Main Components of a TIN

Diagram Shows Components of a TIN
  • Nodes are locations defined by x, y, and z values (xyz) from which a tin is constructed
  • Triangles are formed by connecting each node with its neighbors
  • Edges are the sides of triangles

Developed by: