Elevation models are the backbone of nearly every engineering decision made from aerial data. Yet two of the most common products, the Digital Surface Model (DSM) and the Digital Terrain Model (DTM), are routinely confused, leading to design errors that surface late and cost dearly.
A DSM records the highest reflective surface at every location: rooftops, tree canopy, vehicles and the ground in between. It is ideal for line-of-sight studies, solar shading, and clash detection where everything above ground matters.
A DTM, by contrast, represents the bare earth. Above-ground features are classified out and the remaining ground points are interpolated into a continuous surface. This is what earthworks, hydrology and road design depend on.
The processing difference is significant. Producing a trustworthy DTM requires careful point classification, breakline enforcement along ridges and drainage, and quality control against ground control points. Skipping these steps produces a model that looks correct but misleads the designer.
Our rule of thumb: if your question is about water, earth, or grade, you want a DTM. If it is about objects, visibility, or clearance, you want a DSM. Most projects need both.