Digital Surface Model Vs Digital Terrain Model

What is Digital Terrain Models (DTM)?

A Digital Terrain Model (DTM) is a collection of regularly spaced points and natural characteristics such as ridges and break lines. A DTM adds linear features of the bare-earth topography to a DEM.

In fact, in certain nations, a DTM is used interchangeably with a DEM. This means that a DTM is nothing more than an elevation surface depicting the bare earth in relation to a shared vertical datum.

A DTM (Digital Terrain Model) often complements a DEM by integrating vector representations of natural terrain features such as rivers and ridges. A DTM can be interpolated to create a DEM, but not the other way around.

A digital elevation model (DEM) is a 3D computer graphics representation of elevation data used to illustrate terrain, most typically of a planet, moon, or asteroid. A “global DEM” is a discrete worldwide grid.

Digital Elevation Models (DEMs) are a type of raster GIS layer. Each cell of a raster GIS layer in a DEM has a value related to its elevation (z-values at regularly spaced intervals). DEM data files contain the elevation of the topography across a specific area, typically at a fixed grid interval over the “Bare Earth.”

The distances between each grid point will always be related to some geographical coordinate system (latitude and longitude or UTM (Universal Transverse Mercator) coordinate systems) (Easting and Northing).

Grid points must be closer together to provide more comprehensive information in the DEM data file. The features of the terrain’s peaks and valleys will be better portrayed with modest grid spacing than with very large grid intervals.

DEMs are commonly used in geographic information systems and are the most popular basis for digitally created relief maps.

What is Digital Surface Model (DSM)

DSM (digital surface model) is a topographic digital model that describes the relief and surface situation. A digital surface model (digitized map) is a three-dimensional depiction of the elevations of the Earth’s surface, including natural and man-made items.

It is a raster representation of the surface in x, y and z coordinates. These layers can be used to visualize landscape and terrain, digitally, in order to understand the underlying topography or production areas.

A Digital Surface Model (DSM) is a 3D Computer Graphics representation of the Earth’s lower surface. DSM Computer Model is also known as Digital Terrain Model (DTM).

DSM creation is the process of deriving the Digital Surface Model (DSM) – it is a topographic representation of real-world surface models.

The DSM are based on actual ground control points over a high-resolution aerial photograph (or satellite image). This image must be an ortho photograph or photogrammetric survey (these have a similar look to a DSM).

In the DSM process, the ground control points are selected from the aerial photograph and combined with elevation to form the Digital Elevation Model (DEM). The combination of DEM, ground control points and other information such as slope, area, orientation and boundary conditions are used to create the DSM.

The Digital Terrain Model is derived from digital orthophotography of both surface and vegetation on top of DEM.

Digital Surface Model Vs Digital Terrain Model: In Definition

Digital surface models are three-dimensional computer graphics representations of Earth’s surface, as opposed to digital terrain models, which depict the topography of the surface.

A digital terrain model (DTM) is a three-dimensional representation of the “bulk” of Earth’s surface, including undulations but excluding man-made structures.

Digital Surface Model Vs Digital Terrain Model; In Machines and Technology

Technologies and machines used in DSM

They are:

A DSM creates an image of the world by employing LiDAR (Light Detection and Ranging) or stereo photogrammetry.

Specific radar wavelengths can also be used to generate DSMs.

Light pulses travel to the ground from a LiDAR unit in a LiDAR system. The LiDAR pulses reflect off nearby objects and return to the sensor.

The sensor then calculates the distance traveled by using the time it takes for each pulse to return to the sensor.

For a particular area, LiDAR generates a massive point cloud of elevation measurements. However, height can be determined by tree canopies, buildings, and other characteristics.

That’s when the power of DSMs comes into play.

A DSM records both natural and man-made features on the Earth’s surface, such as changes in tree canopy and vegetation.

This gives you a bird’s-eye view of all the extruding features in a given area.

DSMs can also be made effectively using automated image matching of high-resolution optical stereo pictures or stereo photogrammetry.

When both the exterior and interior orientations of the images are known, stereo matching is used to find corresponding pixels in pairs of images, allowing 3D reconstruction via triangulation.

Technologies and machines used in DTM

They are:

DEMs are typically created using remotely sensed data gathered by satellites, drones, and planes. Because of the variety of DEM source data available, it is possible to fill data gaps in areas where little data is available, such as remote regions.

Automatic DEM extraction from stereo satellite scenes enables the use of data from satellite sensors such as the SPOT-5 (5-10m resolution).

The following are some remote sensing approaches for obtaining DEM surfaces:

– Ground surveying: Using a theodolite, nearby areas are surveyed by assessing known XYZ positions. This necessitates highly specialized work, and, like with DGPS, all points must be interpolated to produce a continuous raster.

– SAR interferometry (also known as InSAR): To create a DEM, synthetic aperture radar (SAR) data collected, for example, by the Shuttle Radar Topography Mission (SRTM), uses multiple radar images from antennas captured at roughly the same time.

Furthermore, others have created DEMs from InSAR and then used deep learning to adjust for urban effect, as seen with the CoastalDEM.

– Digitizing contour lines: DTMs (a subset of DEMs) can be easily digitized with a contour map and then interpolated programmatically with geospatial software.

Digital surface model vs digital terrain model; In Applications

In DSM

The following are some of the applications of DSMs:

– 3D visualization: The DSM is used for 3D visualizations, for example, to visualize a natural environment which may include vegetation and man-made features.

– Risk Assessment: Risk assessment of natural hazards such as flash floods is one of the applications of DSMs.

In the DSM process, based on the DEM and ground control points, a DTM can be derived. It is a raster representation of the surface in x, y and z coordinates.

The 3D view can be used to visualize landscape and terrain, digitally in order to understand the underlying topography or production areas.

In DTM

While a digital surface model (DSM) is beneficial for landscape modeling, city modeling, and visualization, a digital terrain model (DTM) is sometimes required for flood or drainage modeling, land-use studies, geological applications, and other applications, as well as in planetary research.

The digital terrain model can be used to understand landscapes and the Earth surface, digitally. This is required in order to combine this digital elevation data with other datasets (such as satellite imagery) in geographic information systems to understand landscape and terrain digitally.

Digital Surface Model vs Digital Terrain Model: General differences

The general differences are;

1. A digital surface model (DSM) is a three-dimensional computer graphics representation of the Earth’s surface, whereas a digital terrain model (DTM) is a three-dimensional representation of the “bulk” of Earth’s surface including undulations.
2. A DSM provides detail of natural and manmade features on the Earth’s surface, such as changes in tree canopy and vegetation while a DTM is a compilation of raw elevation data expressed in digital form.
3. DSMs can be created based on laser scans and satellite imagery whereas DTMs are created from radiometric information and satellites.
4. DSMs can provide detailed information for different kinds of human activities and activities such as urban, vegetation, and residential areas that cannot be obtained from DTMs.
5. DTM images are often rasterized because of the decimation of DTMs which means that DTMs cannot be navigated and sometimes cannot be projected as a 3D image using either a computer graphics software or a modeling tool.
6. A DSM can highlight differences between two different locations by showing height differences in elevation, whereas a DTM is based on the difference in elevation readings between two different locations.
7. DTMs also capture the changes in terrain when the Earth’s surface has been disturbed such as a landslide. However, DSMs are not able to capture the impact of manmade activities on landscape.
8. DSMs can be used to make very accurate representations of topography, which cannot easily be made using DTMs’ measurements of elevation and depth.
9. DTMs are comparatively inexpensive than DSMs while a DSM can cost more than $1 million per kilometer to produce.
10. DSMs are used in engineering to estimate the stability of a slope, whereas DTMs are used to measure the elevation changes over time and relative to a nominal reference.
11. DSMs provide easier access to information such as elevation and curvature compared with DTM data which can only be accessed using advanced modeling software or geographic information systems (GIS).
12. DSMs enable the viewer to see high-resolution imagery and terrain models combined with high-resolution point cloud data (although this is not always necessary).

Therefore, both DSMs and DTMs play a significant role in the study of Earth’s surface and are useful for various human activities.

DSMs and DTMs FAQs

What is a Digital Surface Model?

A digital surface model (DSM) is a 3D model that describes the physical surface of the Earth.

It is often created from data collected by an aerial or satellite image. It is used in many different applications such as surveying and navigation, for example in flight planning for aircraft.

What are Digital Terrain Models?

A digital terrain model (DTM) consists of a three-dimensional mesh of elevation points on the earth’s surface created based on a combination of raster and vector data. It is often created from a digital elevation model (DEM).

What are the differences between a Digital terrain model and a Digital surface model?

A digital surface model (DSM) is a 3D representation of the Earth’s surface, whereas a digital terrain model (DTM) is a representation of the “bulk” of Earth’s surface including undulations.

Which applications use DTMs?

DTMs are used in geological applications, for example in computer-aided geological mapping to represent landforms. They are also used for flood or drainage modeling, land-use and landscape analysis, and for understanding climate change impacts on the Earth’s surface.

What are the applications of DTM?

The main application of a DTM is to produce elevation maps or contour lines. It could also be used to study weather phenomena such as floods such as measuring the potential impact when it occurs.

What are the applications of DSM?

The main applications of a DSM are in the following areas:

• Natural and environmental sciences, for example to create digital soil maps.
• Land use, for example to create 3D models of buildings, dams, roads and other features.
• Architecture: to create virtual walkthroughs or flythrough of buildings and cities.
• Engineering and surveying: to make 3D models of buildings, roads and land, for example to plan building sites.
• Visualization, for example of the landscape.

What are the advantages of using DEM?

Advantages:

• Using DEM, it becomes easy to visualize three dimensional objects such as smooth hills, mountains and valleys on screen without creating them by hand.
• DEM can be easily manipulated by zooming and panning with a mouse.
• DEM is known as the source of digital surface models.
• It provides various mapping services such as flood inundation prediction, slope stability assessment and erosion hazard assessment.
• It can be used in a variety of applications like irrigation planning, urban expansion, drainage modeling, aircraft approach simulation etc.
• DEM’s accuracy is usually better than contour lines.
• DEM is a good stand-alone product to represent the shape of terrain and land.

Disadvantages of using DEM?

They include:

• It is expensive
• It is not very accurate in representing the surface.
• It does not always provide information about terrain and land
• A DEM does not represent the height of water bodies as it does not capture topography changes in large areas.
• A DEM does not include topographic information of manmade features such as canals, roads, buildings, airports etc.
• There are so many errors when a point is located on a slope or near a contour line.

What are advantages of using DSM?

Advantages:

• DSM provides detailed information about the surface of the Earth. It allows to identify and differentiate between objects such as vegetation, buildings etc.
• DSM is used in engineering applications such as slope stability assessment, drainage modeling and erosion hazard assessment.
• DSM can be used to predict flood inundation.
• It provides a clear image of the surface of Earth.
• DSM can also store surface information about manmade objects such as roads, buildings etc.
• DSM is not very expensive as compared to DEMs.

Disadvantages of using DSM?

They include:

• It does not include the height of water bodies as it does not capture topography changes in large areas.
• It stores only elevation information.
• A DEM is better than a DSM to represent the surface of Earth.
• A DSM does not provide information about objects like vegetation, buildings etc.
• A DSM does not have accurate information about shapes of terrain and land.

What is digital surface model in GIS?

Digital surface model (DSM) is a three-dimensional representation of the elevation of Earth’s surface. It is used in geographical information systems (GIS) to visualize topographic maps. DSM usually uses a digital elevation model (DEM) as its source data.

What is terrain Modelling?

Digital Terrain Models (DTM), also known as Digital Elevation Models (DEM), are computer-manipulated topographic models of the bare Earth. The elevation data of the landscape is stored in the data files in a digital format that corresponds to a rectangular grid.

What is DTM in photogrammetry?

A Digital Terrain Model (DTM) is a set of discrete points with unique height values across 2D points that approximates a portion of the entire continuous terrain surface. DEM is frequently used for elevation models derived from remote sensing (e.g., radar or photogrammetry).

What is digital terrain analysis?

The digital elevation model (DEM), a valuable source of data, is typically used to represent a topographic surface in three dimensions and to mimic key natural geography. DEM has been used in a variety of fields, including physical geography, hydrology, ecology, and biology.

What is DTM in photogrammetry?

A Digital Terrain Model (DTM) is a set of discrete points with unique height values across 2D points that approximates a portion or the entire continuous terrain surface. DEM is frequently used for elevation models derived from remote sensing (e.g., radar or photogrammetry).

What is Topography?

Topography is the measure of elevation, usually in terms of height above or below some arbitrary datum. It can be defined as the distance between points with equal topographic values drawn on a map.