DTM vs DSM: What’s the difference and when should you use each?
If you work with drone data or remote sensing outputs, you’ve probably seen the terms DSM, DTM, and DEM pop up regularly. They all relate to elevation models, but they don’t describe the same thing — and understanding the difference is key to choosing the right one for your project.
A Digital Elevation Model (DEM) is the broad, catch-all term for any dataset that represents the Earth’s surface in 3D. Within this category, you’ll find more specific types of elevation models.
A Digital Surface Model (DSM) captures everything that sits on top of the ground: buildings, trees, structures, and the terrain itself. It gives you a “top of surface” view.
A Digital Terrain Model (DTM), on the other hand, strips all of that away to reveal only the bare-earth surface. Vegetation, buildings, and other above-ground features are removed to show you the true underlying terrain.
Both DSMs and DTMs fall under the DEM umbrella — the right choice simply depends on the questions you’re trying to answer.
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What’s the difference between a DSM and a DTM?
A digital surface model (DSM) captures the elevation of everything on the Earth's surface, including buildings, trees, and terrain. A digital terrain model (DTM) shows only the ground surface, with all above-ground features removed. Both are types of digital elevation models (DEMs), but each serves a different purpose depending on whether you want to analyze surface features or the underlying terrain.
DSM: For capturing surface features
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A DSM includes all the visible features in the landscape. It represents the elevation of the first thing the sensor hits—like treetops, rooftops, and power lines. This makes it useful for:
- Visualizing how a site looks in reality, especially for presentations or stakeholder review
- Assessing tree canopy heights or building elevations
- Performing line-of-sight analysis, shadow modeling, or solar planning
- Urban planning tasks where the interaction between natural and built features matters
If you want to capture how a site appears from above, including man-made structures and vegetation, start with a DSM.
DTM: For understanding the ground
A DTM strips away all surface features and shows just the underlying terrain. It's your go-to when the shape of the earth matters most. Use a DTM when you need to:
- Model water flow, drainage, or flood risk
- Perform slope analysis for grading, stability, or construction planning
- Conduct cut-and-fill or volumetric calculations
- Understand terrain movement or erosion in mining and infrastructure projects
Because DTMs give you a clean representation of the ground, they’re especially important in environmental and engineering contexts where accuracy is key.
Why using the right model matters
Choosing the wrong elevation model can easily steer your analysis in the wrong direction. For instance, if you’re modelling water runoff with a DSM, the presence of trees and buildings can block natural flow paths and give you a distorted result. On the other hand, if you rely only on a DTM to calculate tree height, you’re missing half the picture — the elevation of the canopy itself.
In many workflows, the best approach is to use both models together. By subtracting the DTM from the DSM, you can isolate the height of surface features, which is especially useful when estimating the height of vegetation or buildings.
Can you generate both from drone data?
Yes. Most modern geospatial platforms, including Birdi, allow you to generate both DTMs and DSMs from a single drone capture. That means you can choose the best output for your workflow, or combine them for deeper insights.
For example:
- Use a DTM to calculate stockpile volumes
- Use a DSM to assess vegetation encroachment or roofline views
You can also visualize them side-by-side, layer them with basemaps, and export them for further analysis.
Which one should you use?
If your focus is on the natural shape of the land, use a DTM. If you need to see the full surface environment, including vegetation and structures, go with a DSM.
Still unsure? Ask yourself:
- Are you measuring terrain or surface features?
- Do you need accuracy for modeling or clarity for communication?
- Will this data be used by technical teams, or shared more broadly?
If you’re ever in doubt, starting with both can give you flexibility and a clearer picture of the site.
Want to see how DTMs and DSMs could fit into your workflow?
Book a quick demo and we’ll walk you through how Birdi makes it easy to work with both.