Infrastructure and other AEC projects have begun to exploit large-scale and accurate elevation data. Elevation is an important factor of any earth surface observation. As the accuracy of elevation observations has improved on a larger scale, this data has expanded in value and utility. One of the most used applications of utilizing elevation data is elevation modeling.
Elevation modeling plays a critical role in site planning, site grading, earthwork, quantity estimates, and more. By having a visualization of the landscape of interest with elevation data, engineers will be able to assess their project site, identify the possible problems, and determine the best course of action without paying a visit to the site itself.
There are several ways to model elevation, and in this article, we’re going to focus on three digital elevation datasets in particular - digital surface model, digital terrain model, and digital elevation model.
What is a Digital Elevation Model?
A digital elevation model (DEM) is a gridded raster data and a three-dimensional representation of a terrain, which filters out and excludes terrain vector features (i.e. streams, breaklines, and ridges) and all ground objects, both built (power lines, buildings, and towers) and natural (trees and other types of vegetation).
It is basically the superset of DSM and DTM. A generic term like DEM can be used in most cases because the differentiation between the bare-earth and a surface object is not significant, with DEMs often having spatial resolutions of 20 m or more.
DEMs can be generated from remotely sensed data collected by satellites, drones, and planes and commonly through laser scanning (LiDAR), geodetic surveying, or radar interferometry (InSAR).
What is a Digital Terrain Model?
A digital terrain model (DTM) is a three-dimensional, bare-earth representation of a terrain or surface topography, consisting of an array of points with a defined height, and includes features like rivers, ridges, and breaklines. This model is devoid of the natural or man-made objects located on the earth’s surface, such as vegetation and buildings.
A DTM represents a set of 2D points with specific height values to approximate a part or the whole of a continuous terrain surface with the height values being an approximation of vertical distances between terrain points and some reference surface or geodetic datum.
It is also worth noting that in some countries and fields of research, DTMs are considered as vector data sets and digital elevation models augmented with linear features of the bare-earth terrain (i.e. breaklines, ridges, etc.).
Photogrammetric processing of aerial and space stereo images is commonly used to create DTMs. DTMs can even be created from DSMs using the difference between the height values for trees and buildings and their local neighborhood.
What is a Digital Surface Model?
A digital surface model (DSM) is a three-dimensional representation of the heights of the Earth's surface, including natural or man-made objects located on it. It represents the mean sea level elevations of the reflective surfaces of vegetation, buildings, and other features elevated above the bare earth. It is usually considered as a model of a canopy over the surface of the bare earth.
Photo: GIS Resources (link), All Rights Reserved
Because DSMs depict the bare-earth and all of its above-ground features, they are particularly significant in urban planning. 3D surface models can help in analyzing complex urban scenarios, especially as built-up regions change over time due to urban expansion.
DSMs can be obtained from stereoscopic satellite images, stereoscopic digital aerial photographs with different resolutions, and LiDAR (Light Detection and Ranging) technology.
DEM vs. DTM vs. DSM
The main difference between the three models is that DEM is a 'bare earth' elevation model which is a superset of DTM and DSM, with DTM being a DEM augmented with features like breaklines and ridges while a DSM being a DTM that includes the natural and human-made features on the earth's surface. It is thus important to distinguish between DTM and DSM over vegetated or built areas.
The diagram below shows the differences between a DTM and DSM. Notice how the DTM (orange line) follows the ground, whereas the DSM (green line) follows the structures on the surface, i.e. the top of the house and the tree.
Photo: Heliguy (link), All Rights Reserved
DEMs are used in digital cartography and geographic information systems and are the most common basis for representing terrain. DTMs are often required for flood or drainage modeling, land-use studies, geological applications, and planetary science while DSMs are usually preferred for telecommunications, landscape modeling, city modeling, and visualization applications.
Creating DSMs and DTMs with Plex-Earth
With Plex-Earth, users can easily import DSMs and DTMs directly into their AutoCAD workspace.
Elevation modeling with Plex-Earth
You can see the whole process of importing a terrain through Plex-Earth in this tutorial.
Take note that a terrain imported via Plex-Earth from either Cesium, Terrain Tiles (AWS), or Google Elevations is a digital terrain model.
Digital terrain/surface modeling is becoming an essential tool for many applications in Earth science and engineering. Utilizing the data supplied by elevation models helps engineers in assuring a safe, stable build, and having instant access to reliable elevation information helps in acquiring a more accurate understanding of a project site's morphology and surface which makes it more possible to deliver a timely, effective project outcome, that saves time, money, and stress.
With Plex-Earth, an engineer can easily create DTMs and DSMs for their area of interest in a matter of seconds, straight into their AutoCAD environment.
We hope that you have found this article about elevation modeling, helpful. Feel free to contact us at email@example.com for any questions you may still have.
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