Real-Time Terrain Following vs. High-Resolution DEM

By Kristaps Brass, Product Owner, UgCS

Let’s talk about terrain following — not in theory, but in practice. As drones become more deeply integrated into professional data acquisition workflows, terrain awareness is no longer a “nice-to-have.” It’s mission-critical. But not all terrain following is created equal.

At UgCS, I work directly with drone pilots flying everything from LiDAR scanners to ground penetrating radar systems. And one of the most common questions I get is this: Should I rely on real-time terrain following, or is a preloaded high-resolution digital elevation model (DEM) enough?

The answer isn’t one or the other. It’s about using the right method for the right mission.

What We Mean by Terrain Following
Let’s start with the basics. Terrain following is the ability of a drone to maintain a consistent height above the ground, not above sea level, not a fixed altitude, but a fixed AGL (above ground level).

This matters because most sensors, from LiDAR to GPR, produce usable data only when flown at a specific range from the ground. Too high or too low, and you lose resolution, quality, or in some cases, the entire data set.

Terrain following can be handled in two ways:

1.    Flying according to a DEM.

2.    In real-time, using onboard sensors or altimeters to adapt dynamically during flight.

Each has its place — and choosing wrong can compromise your data. All depends on the sensor, terrain and desired flight altitude.

When Real-Time Terrain Following Is the Right Tool
Real-time terrain following is essential when you’re flying extremely low and can’t tolerate any error between the planned altitude and the real surface. This is typical when using:

●    Ground Penetrating Radars (GPR)

●    Metal detectors

●    Echosounders for shallow water

●    Any low-altitude sensor on a drone-integrated payload system

These sensors often operate below 5 meters AGL, and sometimes even closer. At that range, even the best DEM won’t save you if the terrain varies unexpectedly. Grass, small rocks, vegetation — they all matter. You need real-time correction.

We’ve seen this in the field with integrated GPR systems. One project in northern Europe involved scanning underneath glacial sediment — the sensor had to fly at 2–3 meters. Real-time terrain following was the only option. A pre-calculated elevation profile would have missed surface variation entirely, especially at that scale.

That’s why we support real-time terrain following in UgCS via systems like radar or laser altimeters. But it comes with tradeoffs — onboard terrain sensors can be affected by surface reflectivity, water, vegetation, or harsh light. Pilots need to test and calibrate carefully.

When a Good DEM Is All You Need
For most mapping, LiDAR, and photogrammetry missions, a quality DEM is more than sufficient. Especially if you’re flying at 30–120 meters AGL, the granularity of the elevation model is well within your safe margin.

UgCS comes out of the box with 30-meter global DEM data, which works well for large-area surveys, agriculture, and general terrain following. In the United States, we use 10-meter resolution DEMs, based on the USGS 1/3 arc-second dataset.

Even in LiDAR flights — where consistency of scan height is critical — a good DEM can handle the job as long as the terrain isn’t unusually complex.
The key here is scale. If you're flying at 60 meters, even a 10-meter DEM will keep you within 1–2 meters of your planned altitude, which is usually acceptable for topographic modeling.

When to Upgrade to High-Resolution DEM
Now, if you’re flying in very rugged terrain — steep cliffs, deep valleys, dense vegetation — even 10-meter DEMs can leave you exposed. The drone might lose AGL consistency or, worse, clip the terrain on a sharp drop or ridge.

This is where high-resolution DEMs (1 meter or better) come into play.

UgCS supports importing custom DEMs in GeoTIFF format. We’ve had customers integrate LiDAR-based DEMs, drone-generated photogrammetry surfaces, or publicly available 1-meter grids into the planning environment. The improvement is immediate — tighter AGL control, safer flights, and more consistent sensor altitude.

For instance, one operator in the Alps used a 1-meter resolution DEM derived from a previous photogrammetry survey to plan vertical façade inspections on a dam wall. The difference between flying with and without the high-res surface was the difference between confidence and guesswork.

My recommendation? If your drone is flying within 10–15 meters of the surface in terrain with fast vertical changes, or if your payload requires very consistent ground distances, you’ll want that higher-res DEM.

Final Thoughts: Know Your Mission, Choose the Right Tool
There’s no one-size-fits-all answer when it comes to terrain following. Anyone who tells you otherwise hasn’t flown enough real missions. The right choice depends on your altitude, sensor, terrain, and tolerance for error.

●    If you’re flying 3 meters off the ground with a metal detector, you need real-time terrain following.

●    If you’re flying 60 meters with a LiDAR scanner in gently rolling terrain, a 1 arc-second DEM will serve you just fine.

●    If you’re flying near cliffs, buildings, or sharp terrain transitions — bring a high-res DEM or exercise extreme caution when flying and be ready to stop the drone at any point.

UgCS gives you options because professional missions demand it. We’ve designed our terrain-following engine to adapt to how professionals actually work — not how drone marketing claims it works.

As always, the safest mission is the one you’ve planned with your specific equipment and terrain in mind. Start with what you know, and adjust from there.
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Kristaps Brass is an Engineer and Product Owner of UgCS at SPH Engineering. Having been with SPH Engineering since 2014, Kristaps has worked on countless field flight tests, lead customers training in Riga and around the world (from Brazil to Australia), and even participated in an expedition to Greenland in 2019 together with Alexey Dobrovolskiy, CTO. Kristaps graduated from Stockholm School of Economics in Riga and Tallinn University of Technology where he studied Integrated Engineering. He is currently heading the UgCS development and product team toward making UgCS flight planning software the leading choice for professional drone pilots.