DEM, DTM and DSM are all digital models of height, and mixing them up can lead to wrong volumes, levels and designs. Here is what each one means in practice.
The three models
- DSM (Digital Surface Model): the top of everything, including trees, buildings and towers.
- DTM (Digital Terrain Model): the bare ground with those objects removed, used for engineering.
- DEM (Digital Elevation Model): a general term for a height grid. Different people use it for either surface or terrain, so always ask which is meant.
Which one do you need?
| Use | Model |
|---|---|
| Road and rail alignment, drainage, contours | DTM |
| Earthwork volumes on cleared ground | DTM |
| Obstruction and line-of-sight studies | DSM |
| Tree heights | DSM minus DTM |
LiDAR or photogrammetry?
LiDAR sends laser pulses, and some pass through gaps in vegetation to reach the ground. This makes it the better choice for a DTM under tree cover. Photogrammetry builds height from photos, so it mainly sees the visible surface. It can work well on open, bare sites.
How a DTM is produced
- Establish GNSS ground control.
- Fly the drone mission and capture the point cloud.
- Classify points into ground, vegetation and buildings.
- Build the DTM and DSM from the classified points.
- Generate contours and cross-sections, and check against control.
See also: LiDAR drone survey vs total station.
FAQ
Is DEM the same as DTM?
Not always. DEM is a general term, while DTM clearly means bare ground. Confirm in your scope which one will be delivered.
Can contours be made from a DSM?
They can, but they would follow trees and buildings. Engineering contours should come from a DTM.
What file formats are delivered?
Commonly GeoTIFF for grids, LAS or LAZ for point clouds and DWG or DXF for contours.
Talk to our team
Need a DTM for your site? Call +91 98718 04288, email contact@geowingseng.com or see our LiDAR drone survey service.
