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Terrain Data

Terrain data is usually expressed as a series or collection of elevation points with x-, y-, and associated z-values. It generally includes a series of points representing the high and low extremes in the terrain that define topographic features such as streams, levees, ridges, and other phenomena. Terrain data are critical in areas such as infrastructural management, hydrology and flow-direction studies, and land-use planning.

Some of the major uses of terrain data are as follows:

  • Modeling water flow or mass movements (e.g., landslides)
  • Creating physical models (such as raised-relief maps)
  • Rectifying aerial photography or satellite imagery
  • Rendering 3D visualizations, etc

Digital Elevation Models (DEMs)

Elevation grids, sometimes called DEMs (Digital Elevation Models), are commonly used to represent ground terrain surfaces. Elevation grids use a fixed grid cell size to create a raster heightmap (a grid of squares) in which each cell stores the corresponding ground elevation. The smaller these grid cells, the greater the level of detail captured by the DEM data files.

Supported Terrain Data Sources

CivilGEO’s software supports most of the terrain elevation sources used for generating terrain surfaces. In the Terrain source entry of the Generate Terrain dialog box, different supported terrain source types are shown below.

Adding Supported Elevation Data Formats

CivilGEO’s software allows the user to access elevation data using three primary methods, as appear below.

  1. Local File Elevation Data
    Our software supports most of the major elevation grid data file formats, such as:

    • ArcInfo ASCII Elevation Grids
    • ArcInfo Binary Elevation Grids
    • GeoTIFF Elevation Grids
    • USGS DEM Elevation Grids
    • USGS NED Elevation Grids – BIL Format
    • USGS NED Elevation Grids – Float Format
  2. Online Elevation Data
    Our software allows the user to utilize elevation data directly either from the USGS or NASA elevation data servers, as mentioned below.

    • United States Elevation Data (10m) – USGS accesses the elevation data from the USGS National Elevation Dataset (NED) data server Different parts of the United States have different elevation resolutions. The National Elevation Dataset (NED) is the primary elevation data product of the USGS. It is a seamless dataset with the best available raster elevation data of the conterminous United States, Alaska, Hawaii, and territorial islands.
    • Worldwide Elevation Data (30m) – NASA accesses the elevation data from the NASA elevation data server Different parts of the world have different elevation resolutions. The SRTM obtained elevation data on a near-global scale to generate the most complete high-resolution digital topographic database of Earth. The SRTM consisted of a specially modified radar system that flew onboard the Space Shuttle Endeavour during an 11-day mission in February 2000.
  3. Download Elevation DEM
    CivilGEO’s software allows the user to download elevation DEMs for a particular area. While downloading the elevation DEMs, the user can select the custom area from the scenario either automatically or interactively by picking the user-defined area from the Map View as shown below.

Terrain commands

Our software provides the user with numerous commands that work with elevation data, as mentioned below.

Government and Commercial DEM Sources

The two broad categories of DEM sources are as follows:

  1. Government sources
    The major government sources to download DEMs are mentioned below.

    • USGS: USGS accesses the elevation data from the USGS National Elevation Dataset (NED) data server. The Digital elevation data for the United States and its territories are available through The National Map Downloader.
    • NASA: NASA’s Space Shuttle Radar Topography Mission (SRTM) uses synthetic aperture radar and interferometry to collect one of the most accurate digital elevation models of Earth. It covers most of the world with an absolute vertical height accuracy of less than 16m. The SRTM data is freely available on USGS Earth Explorer.
    • NRCS: Types and sources of elevation data commonly used for NRCS applications are Digital Elevation Models (DEM) and the National Elevation Dataset (NED). These data have 10-, 30-, and 3-meter resolution and are available via the USGS and USDA websites. The USGS offers a central website for downloading digital elevation data in Geographic and NAD83 formats via the National Map.
    • Ontario Lidar Digital Terrain Model (DTM) Land Information Ontario (LIO): This dataset is a raster product representing the bare-earth terrain derived from a classified LIDAR point cloud. This DTM data is available in the form of 1-km by 1-km non-overlapping tiles grouped into packages for download.
  2. Commercial sources
    The major commercial sources to download DEMs are mentioned below.

    • L3HARRIS: L3HARRIS geospatial offers a wide variety of in-house digital elevation datasets and has partnered with other leading topography providers for the multi-resolution Digital Elevation Models (DEM) coverage of Earth.
    • Cloudeo: Cloudeo’s Intermap DEM provider facilitates a 3D terrain dataset that provides seamless data for the entire USA at the one-meter resolution.
    • UP42: The UP42 service partnered with Intermap provides high-quality digital surface models (DSM) and digital terrain models (DTM) that enable 3D solutions with or without surface objects, such as buildings or vegetation.
    • MAXAR: MAXAR is also one of the sources for high-quality 3D surface models, digital surface and terrain models, etc.

Terrain Measurement Techniques

The different terrain measurement techniques employ elevation data, usually in conjunction with other geospatial information, to describe the landscape for basic visualization, modeling, or to support decision making. The major terrain measurement techniques are as follow:

  • Direct survey: In this surveying method, the X, Y, and Z coordinates are measured using onsite manual efforts. This method requires expertise to measure the terrain points to generate a continuous raster.
  • Drone survey: Drones can make accurate maps by combining images, which can be interpolated into three-dimensional imagery with software that utilizes photogrammetric techniques to form orthomosaics and digital surface models.
  • LIDAR scanners: Light detection and ranging (LIDAR) also known as Laser altimetry. This terrain measurement technique measures the reflected light that has bounced off the ground to determine the elevation of the Earth’s surface.
  • Bathymetric survey: This survey measures the depth of a water body and maps the underwater features of a water body. Multiple methods can be used for bathymetric surveys, including multi-beam and single-beam surveys, Acoustic Doppler Current Profiler (ADCPs), sub-bottom profilers, and the EcoMapper Autonomous Underwater Vehicle (AUV).

About the Author Chris Maeder

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