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Photogrammetry

DTM / DEM

Terrain and surface models with breakline capture and manual editing, not raw correlation output.

DTM / DEM — representative deliverable
Overview

DTM / DEM

Automated image correlation produces a dense surface quickly and gets terrain wrong in entirely predictable places: under vegetation, on water, at building edges, in shadow, and anywhere texture is low. Delivering raw correlation output as a terrain model is the most common shortcut in this field.

We generate the dense surface and then edit it. Vegetation and structures are removed to produce true bare-earth terrain. Water bodies are flattened and given hydrologically sensible levels. Breaklines are captured where the terrain has genuine discontinuities, so ridges, kerbs and banks survive into the final surface instead of being smoothed away.

Both DTM and DSM are available, and the distinction is maintained rigorously — a DSM that has had some vegetation removed is neither product and is useless for volumetrics or hydrology.

What you receive

Every item below is issued in your own template, with your layer conventions, title block and revision scheme.

  • Dense surface generation from stereo image correlation
  • Edited bare-earth DTM with vegetation and structures removed
  • DSM retaining canopy and built form where required
  • Breakline capture at genuine terrain discontinuities
  • Water body flattening with hydrologically consistent levels
  • Void filling with the method and extent documented
  • TIN and grid output at the specified resolution
  • Contour generation from the edited surface
  • Vertical accuracy report against independent check points
  • Hillshade and slope derivatives on request

Production detail

Typical turnaround2–5 weeks by area and edit intensity
Grid resolutions0.1 m to 30 m as specified
Vertical accuracyImagery-dependent; typically 0.3–1× GSD in open terrain
EditingManual bare-earth editing, not raw correlation output
Void handlingInterpolated with method and extent documented per void
Output formatsGeoTIFF, ASCII grid, LandXML TIN, DWG, LAS, XYZ
RevisionsTwo rounds included

Software and formats

We work in your toolchain. If something you use is not listed, ask — the list below is only what we use most.

Trimble Inpho / MATCH-TAgisoft MetashapeSOCET SETGlobal MapperArcGIS ProCivil 3DPython / GDAL

Frequently asked

Editing. Automated correlation cannot reliably distinguish ground from low vegetation, gets building edges wrong, and fails on water and in shadow. Our DTM has been reviewed and corrected in those areas, which is most of the cost and all of the difference in usability.

Yes, and UAV data gives excellent resolution over small areas. The constraint is vegetation — image-based methods cannot see ground under canopy at all, so for wooded sites we will tell you that LiDAR is the right tool rather than sell you a surface that guesses.

Flattened to a constant level per water body, with levels set hydrologically consistently so a lake does not sit above its inflow or below its outflow. Raw correlation over water is essentially noise and is replaced rather than smoothed.

Yes, and we keep the distinction clean. The DSM retains canopy and built form; the DTM is edited bare earth. A half-edited surface is neither and cannot be used for either volumetrics or hydrological modelling.
Planimetry Orthophoto Generation
Step 3 of 4 in Photogrammetry

Send one dtm / dem job and see how we work

Scope, price and programme come back in writing before anything starts. Most first projects are a single deliverable so you can judge us on output, not on a pitch.

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