Orthomosaic, DSM & DTM Explained

What is an orthomosaic?

An orthomosaic is a single, seamless aerial image of your whole site, stitched from many photos and geometrically corrected so it's to scale and distortion-free. Unlike a normal photo — where things lean and scale changes across the frame — every point on an orthomosaic sits in its true position, so you can measure distances and areas directly on it. It's delivered as a georeferenced GeoTIFF (often a cloud-optimised COG).

What is a DSM (Digital Surface Model)?

A DSM records the elevation of the top surface of everything — ground, buildings, trees, stockpiles, machinery. Each pixel stores a height. DSMs are what you use for line-of-sight, canopy and stockpile work, and they're the basis for most volume calculations.

What is a DTM (Digital Terrain Model)?

A DTM (or DEM) is the bare earth — the ground surface with buildings, vegetation and objects removed. It's what civil engineers design against: grading, drainage, contours and cross-sections all come from the DTM. Deriving a good DTM from a DSM means filtering out everything that isn't ground.

DSM vs DTM — which do you need?

Simple rule: DSM = everything, DTM = ground only. Use the DSM for stockpile volumes, canopy height and anything on top of the ground; use the DTM for terrain design, earthworks, drainage and contours. Many projects need both, and Orthosite generates both from one flight.

Point cloud and 3D mesh

The point cloud (LAS/LAZ) is the raw 3D — millions of measured points you can classify, section and feed into CAD. The 3D mesh (OBJ) is a continuous, photo-textured surface built from the cloud, ideal for inspection and presentation. The orthomosaic and elevation models are, in effect, tidy 2.5D products derived from this same 3D reconstruction.

Derived products: contours, volumes, profiles

From these core outputs you get the day-to-day deliverables: contours (iso-height lines from the DTM/DSM), volumes (cut/fill from a surface), and cross-section profiles (a slice of elevation along a line, for roads and drains). Orthosite creates all of these in-browser and exports them in open formats in your coordinate system.