Digital elevation model

Computers can make maps of the ground.

These maps show hills and valleys. Some maps show trees and buildings too.

Other maps show only the bare ground. This helps people study how water flows.

Computers use numbers to show height. They can turn these numbers into colors. Green might show low land. Red might show high land. These maps help us see our world.

Computers can make 3D models of the land. We call these digital elevation models, or DEMs.

These models use numbers to show height. They help us see mountains and valleys on Earth or even on Mars.

There are different types of models. A digital surface model, or DSM, shows everything on the ground. This includes rooftops and tree tops.

A digital terrain model, or DTM, shows only the bare ground. Scientists use special math to remove buildings from a DSM to make a DTM. This is called bare-earth extraction.

How do we get this data? We often use remote sensing. This means using tools from far away, like satellites or drones.

Some satellites use radar to measure the ground. Other tools use lasers. This is called laser altimetry.

These models are very useful. They help us plan roads or see how water flows during a flood. They even help us fly planes in a simulation.

A digital elevation model, or DEM, is a 3D computer version of land.

It uses height data to show the shape of mountains or valleys. These models can represent a whole planet, a moon, or even an asteroid.

Scientists use them in geographic information systems, which are computer tools for maps. They are the most common way to make digital relief maps. These maps help us see the texture of the world.

There are two main ways these models show the surface. A digital surface model, or DSM, shows everything on top of the ground. This includes things like tree tops or building roofs.

A digital terrain model, or DTM, shows only the bare ground. To make a DTM, scientists use math to filter out objects. This step is called bare-earth extraction.

Some people use DEM as a general name for both types. A DSM is great for looking at cities or forests. A DTM is better for studying how water flows or how floods happen.

We can build these models in many ways. Many people use remote sensing, which means collecting data from far away.

Satellites can use radar to measure the earth. Other tools use lasers, which is called laser altimetry.

Some models are made using a grid of squares. This is called a raster. Other models use a network of triangles. This is called a triangular irregular network, or TIN. You can also use drones or land surveying to get the numbers.

Space missions have given us many important datasets. The SPOT 1 satellite from 1986 provided the first large maps of land.

Later, the Shuttle Radar Topography Mission, or SRTM, sent data in 2000. The ASTER instrument on the Terra satellite also sent data in 2000.

We even have maps of other worlds. The MOLA tool mapped Mars, and the LOLA tool mapped the Moon.

The New Horizons mission even made maps of Pluto.

These models connect to many parts of our daily lives. They are used to help planes fly in simulations.

Engineers use them to design roads and bridges. They also help with satellite navigation, like GPS.

Farmers use them for precision farming in their fields. Even archaeologists use them to study old sites. These digital maps turn piles of numbers into a world we can see.

A digital elevation model, often called a DEM, is a 3D computer graphics representation of elevation data.

These models represent the shape of terrain or overlaying objects on a planet, moon, or asteroid. They serve as the primary basis for digitally produced relief maps. Scientists frequently use them within geographic information systems, or GIS, to study the Earth. Because they turn raw height measurements into visual shapes, they are essential for understanding the physical world.

There are specific ways these models define the surface being measured. A digital surface model, or DSM, represents the entire top layer of a landscape. This includes objects like building roofs or the canopy of a forest.

In contrast, a digital terrain model, or DTM, represents only the bare ground surface. To create a DTM, researchers use complex algorithms to remove objects like plants and buildings. This specific process is known as bare-earth extraction. While some scientists use these terms interchangeably, the distinction is vital for different types of research.

Data can be organized into different mathematical structures. One common method is the raster, which is a grid of squares known as a heightmap. In this format, each square contains a specific elevation value. Another method is the vector-based triangular irregular network, or TIN. A TIN uses a network of connected triangles to represent the surface. Because of these different structures, some researchers call a TIN a primary or measured DEM, while a raster is often called a secondary or computed DEM.

Creating these models requires various advanced collection techniques. Many DEMs are built using remote sensing, which is the collection of data from a distance. One powerful technique is interferometric synthetic aperture radar, or InSAR. This involves using radar satellites to collect data that can generate maps tens of kilometers wide. Another method uses stereoscopic pairs, where two optical images are taken from different angles. This can be done by an airplane or an Earth Observation Satellite.

Space exploration has provided some of our most significant elevation datasets. In 1986, the SPOT 1 satellite provided the first usable elevation data for a large portion of Earth's landmass. In the year 2000, two major projects provided even more data. The Shuttle Radar Topography Mission, or SRTM, used single-pass radar. At the same time, the ASTER instrument on the Terra satellite used double-pass stereo pairs. These missions allowed scientists to map much larger areas with high precision.

We also use these tools to map other worlds in our solar system. Scientists use orbital altimetry, which is the measurement of distance from an orbit, to map planets. This often involves laser altimetry, or using lasers to measure height. For example, the Mars Orbiter Laser Altimeter, known as MOLA, mapped the surface of Mars.

Similarly, the Lunar Orbital Laser Altimeter, or LOLA, mapped the Moon. Even distant bodies like Pluto have been mapped using stereo photogrammetry by the New Horizons mission.

To make these models useful for humans, the data must be rendered visually. A DEM is actually just a matrix of numbers, but we can turn it into a map. One way is through shading and false color assignment, also called pseudo-color. For instance, a map might use green for low elevations and red for higher ones.

Scientists sometimes use vertical exaggeration to make subtle changes in height more noticeable. However, some researchers object to this because it can make the landscape look misleading.

Digital elevation models connect to many modern technologies and fields. In engineering, they help with infrastructure design and analyzing how water flows during floods. They are also critical for satellite navigation systems like GPS and GLONASS. In transportation, they assist with flight simulations and intelligent transportation systems. Even in agriculture, they support precision farming. From archaeology to studying how landslides move, these models provide a digital window into the structure of our world.