WHAT ARE DTM, DSM & DEM?

Elevation Models in GIS Made Easy

In our previous LiDAR related article, we gave a 101 course in LiDAR – if you missed it and are in dire need of basic knowledge of LiDAR, you can read it from here. 101 in LiDAR is highly recommended, as it will facilitate the easier understanding of the following content. However, if you are already familiar with the LiDAR technology, the 101 course can be skipped.   

If you have been following the GIS industry closely, you have most probably come across the agronym’s DTM, DSM and DEM. We at Gisica also offer DTMs, DSMs and DEMs as data processing services to our customers. These three acronyms stand for Elevation Models commonly used in the GIS Industry. The acronyms come from Digital Terrain Model (DTM), Digital Surface Model (DSM) and Digital Elevation Model (DEM).   

We created a table with simple definitions for DTM, DSM and DEM. The purpose of the table is to make it easier to differentiate these three from one another:  

DIGITAL TERRAIN MODEL (DTM)

  • DTM is a three – dimensional representation of a terrain surface 
  • It includes heights, elevations and other geographical elements and natural features such as rivers and forests
  • More applicable for GIS and cartographic representations 

DIGITAL SURFACE MODEL (DSM)

  • DSM represents the earth’s surface and therefore includes all objects on it 
  • Commonly used in LiDAR applications 

DIGITAL ELEVATION MODEL (DEM)

  • DEM refers to a raster or regular grid of spot heights
  • A raster can be a digital aerial photograph, imagery from a satellite, a digital picture or even a scanned map
  • Commonly used in LiDAR applications  

Now that we know the basic definitions of them, it is time to get to know these three methods in depth.

Digital Terrain Model (DTM)

Digital Terrain Model represents the Earth’s surface and contains topographic information. This information includes natural features, such as rivers, slopes, lakes, valleys and forests. What makes DTM unique is that it can be interpolated to generate a DEM. Also, DTMs are more used for GIS and cartographic representation than for LiDAR applications.  

Digital Terrain Models are typically used to create topographic maps. A DTM is also used for flood modeling, land-use planning and geological applications.

Picture from Meissen after the Elbe River started flooding. A DTM is also used for flood modeling to be better prepared to similar situations.

Digital Surface Model (DSM)

Most LiDAR applications make use of DSM and DEM. A Digital Surface Model includes all the objects on the earth’s surface. LiDAR delivers a massive amount of point clouds and a DSM captures all the natural and built features. This is useful when creating a 3D model, which is used for telecommunications, urban planning and aviation. 

DSM is used in aviation to determine any obstructions on a runway. Another good use for the elevation model is to manage vegetation as it can point out where and how much of vegetation is intruding into unwanted places. In city planning DSM is a very widely used tool. It helps to see how a planned building would affect the surroundings.

Digital Elevation Model (DEM)

Digital Elevation Model (DEM) refers to a raster or regular grid of spot heights. A raster can be a digital aerial photograph, imagery from a satellite, a digital picture or even a scanned map. A digital elevation model is commonly used in LiDAR applications. A DEM can be generated using a DTM, but not vice versa.  

In a digital elevation model non-ground points, such as bridges and roads, are filtered out. In a DEM the built (such as buildings) and natural features (vegetation) are not included. This bare-earth elevation model is particularly useful when planning land and soil use. 

In soil mapping DEMs are used to mapping soils. Also, when planning a new road, DEM’s are very useful in areas that have a high slope and have a very high risk of avalanches.

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