DTM vs DSM: What’s the difference and when should you use each?

When you're working with drone data or remote sensing outputs, you’ll often come across terms like DSM, DTM, and DEM. They all refer to elevation models, but they’re not all the same.

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Let’s clear it up:

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• DEM (Digital Elevation Model) is often used as a general term for any elevation dataset that models the Earth's surface in 3D.
• DSM (Digital Surface Model) is a type of DEM that includes all visible surface features, like buildings, trees, and terrain.
• DTM (Digital Terrain Model) is another type of DEM, but one that shows only the bare-earth ground surface, with all features removed.

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So, DSMs and DTMs are both specific types of DEMs, and the one you use depends on the job you’re trying to do.

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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.

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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:

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• 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

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If you want to capture how a site appears from above—including man-made structures and vegetation—start with a DSM.

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DTM: For understanding the ground

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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:

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• 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

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Because DTMs give you a clean representation of the ground, they’re especially important in environmental and engineering contexts where accuracy is key.

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Why using the right model matters

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Using a DSM instead of a DTM, or vice versa, can lead to the wrong conclusions. For example:

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• If you're modeling water runoff using a DSM, the trees and buildings will block natural flow paths, distorting the analysis
• If you're trying to calculate tree height using a DTM alone, you’ll miss the key part: the elevation of the tree canopy

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In many cases, using both together is ideal. Subtracting the DTM from the DSM gives you the height of surface features—helpful for estimating tree or building height.

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Can you generate both from drone data?

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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.

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For example:

• Use a DTM to calculate stockpile volumes
• Use a DSM to assess vegetation encroachment or roofline views

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You can also visualize them side-by-side, layer them with basemaps, and export them for further analysis.

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Which one should you use?

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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.

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Still unsure? Ask yourself:

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• 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?

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If you’re ever in doubt, starting with both can give you flexibility and a clearer picture of the site.

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Want to see how DTMs and DSMs could fit into your workflow?

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Book a quick demo and we’ll walk you through how Birdi makes it easy to work with both.

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