There are numerous uncertainties that arise when it comes to measuring heights in surveying. There are different surveying models, and the model to choose for the specific requirement is a critical decision to make in the GIS domain.
In this blog, we will glance into three of the most popularly used elevation models, namely:
- DEM (Digital Elevation Models)
- DSM (Digital Surface Models)
- DTM (Digital Terrain Models)
And how each method varies conceptually.
So, let’s get straight to the topic at hand.
1.What is the Digital Elevation Model (DEM)?
The DEM is a raster grid that refers to a vertical datum that shows the earth in its naked form. The non-ground points such as roads, infrastructures such as buildings and bridges are filtered out. The elements of nature like trees and other forms of vegetation are also not included in the DEM output.
The DEM model has a wide range of applications in fields of research such as:
In the domain of hydrology, technicians use DEM to calculate flow accumulation and flow direction and delineate watersheds.
Mapping of soil can be carried out as a function of elevation and considering geology, climate, and time parameters.
Assessing Stability of Terrain
During the planning phase of construction projects such as highways and residential colonies, DEM can be leveraged to analyse terrain stability and check if the land is prone to natural disasters such as landslides or avalanches, especially in high slope areas.
2.What is the Digital Surface Model (DSM)?
To understand the concept of DSM, let’s revisit how LiDAR technology works. In any LiDAR system, the light pulses from the source bounce off different target surface(s) and return to the sensor.
The end product is a point cloud that consists of varying elevation values that may come from tree canopies, buildings, power lines, electric towers, etc. The DSM captures these natural and artificial features present on the earth’s surface.
DSM is widely applied in 3D modelling used in urban planning, aviation science, and the telecom sector. Some of the primary applications are listed below:
DSM systems can be used to visualise the location and volume of vegetation present along a transmission line.
Runway Safety In Aviation
DSMs can be used to check if there are any obstructions present along the runway in an airport or aviation academy to avoid potential mishaps.
View From Building
Urban planners often use the DTM technique to understand how a proposed building will affect the viewshed (view from a vantage point) with respect to the residents or businesses in that area.
3. What is the Digital Terrain Model (DTM)?
As per the USGS LiDAR Base Specification, the DTM mode can be defined in two ways based on your region of residence.
In countries like the USA and Turkey, DTM has a separate meaning, while in other places, it is similar to the DEM mode we discussed earlier in this blog. DTM is a more data rich form of DEM by adding linear properties to the bare earth terrain.
DTM is a vector set that consists of dot representations that are regularly spaced. At the same time, the natural features like a mountain or a river are shown as contour lines between these dots in the vector data.
DTMs are created using the technique of Stereo Photogrammetry. It is capable of showing distinct terrain features due to the presence of 3D points at regular intervals and 3D refraction lines.
It has applications in assessing the earth’s natural processes, floods and water infiltration, vegetation distribution, and large insurance firms use it to assess the scope for damage cover.
Artificial processes like telephone tower siting, forest observation points, and viewshed assessments can also be accomplished using the DTM concept.
Wrapping It Up
We hope you have got a brief insight into the three different models of elevation in GIS surveying. It is imperative to choose a suitable model based on your GIS needs.
All the three techniques we discussed here are powerful in their way, with numerous applications across domains.