Key takeaways
- An orthomosaic is a measurable map, not a photo — a point cloud is the 3D measurement, and the two answer different questions.
- DSM includes everything on the surface (trees, buildings, stockpiles); DTM is bare earth. Asking for the wrong one is the most common deliverable mistake.
- Agree the file formats before the flight — a beautiful deliverable your engineer's software cannot open has no value.
Most people booking a first drone survey know what they want to learn — a stockpile volume, a set of contours, a progress record. Fewer know what will actually land in their inbox afterwards, or which of those files their engineer, surveyor or accountant will end up using.
That gap causes real friction. A client receives a beautiful 3D mesh and discovers their civil team needed a bare-earth surface. Or a point cloud arrives in a format their software will not open. None of it is hard to avoid — it just has to be decided before the aircraft flies, not after.
Here is what each deliverable actually is, and who each one is for.
Orthomosaic — the measurable map
An orthomosaic is built from hundreds of overlapping photos, each geometrically corrected so that perspective distortion is removed, then stitched into one continuous image. The result looks like an aerial photo but behaves like a map: every pixel sits at a known ground position, so you can measure distances and areas directly on it.
That distinction matters. A single aerial photo has perspective — objects lean away from the centre and scale changes across the frame, so measuring on it produces wrong numbers. An orthomosaic does not.
Who it is for: anyone who needs a current, measurable plan view — site planning, area take-offs, progress records, permitting exhibits, marketing imagery.
Point cloud — the 3D measurement
A point cloud is millions of individual points, each with a coordinate and usually a colour. It is the raw three-dimensional record of the site, produced either from photogrammetry or from a LiDAR sensor.
Nearly every other 3D deliverable is derived from it. Surfaces, contours, volumes, cross-sections and CAD linework all start here, which is why it is worth receiving and keeping the point cloud even when it is not the file you work in day to day.
Who it is for: surveyors and engineers who will do their own analysis, and anyone who wants the option of asking new questions of the same flight later without re-flying.
DSM vs DTM — the one people get wrong
Both are surface models. The difference is what they include, and it is the single most common source of a disappointing deliverable.
- DSM (Digital Surface Model) — the top of everything. Tree canopy, buildings, equipment, stockpiles. If you want to measure a pile, this is the surface that has the pile in it.
- DTM (Digital Terrain Model) — bare earth, with vegetation and structures classified out. If you want to design a grade, a road or a drainage plan, this is the surface your engineer needs.
Producing a good DTM requires the survey to actually see the ground. In heavy vegetation, photogrammetry cannot see through canopy at all, which is one of the practical reasons LiDAR is chosen for some sites. If your deliverable list says DTM and the site is heavily vegetated, that is a conversation to have before the flight rather than after.
Contours and cross-sections
Contours are generated from a surface model at whatever interval you specify. The interval should be driven by what the drawing is for — a tight interval on a rough site produces a drawing nobody can read, and a coarse one hides the detail a designer needs.
Cross-sections along a defined alignment come from the same surface and are usually what a road, ditch or pad design actually consumes.
Volumetric report
For stockpile measurement, the deliverable that matters is the volume report: each pile identified, its volume, and — critically — a statement of the base surface the volume was calculated against.
That last part is what makes a number defensible. A pile volume is always measured relative to some base: a surveyed pad, a modelled base plane, or a previous survey's surface. Two honest surveys of the same pile can differ simply because they used different bases. A volume with no stated base is a number without a definition.
Who it is for: inventory reconciliation, year-end reporting, and anyone whose number will be reviewed by an auditor or a client.
3D mesh model
A mesh turns the point cloud into a continuous textured surface — the deliverable that looks impressive in a presentation and rotates smoothly in a viewer. It is genuinely useful for communication: showing a site to a board, a landowner or a public meeting.
It is generally not the file your technical team measures in. Treat it as the communication deliverable, not the measurement one.
Agree the formats before the flight
This is the practical part that saves the most trouble. Ask your engineer, surveyor or GIS person exactly what they want to receive, and confirm it in writing before the survey:
- Coordinate system and vertical datum. The single most important item on the list. Deliverables in the wrong projection are not a small fix.
- Point cloud format — and whether classified or unclassified.
- Raster deliverables for orthomosaic and surface models, and whether georeferencing sidecars are needed.
- CAD deliverables for contours and linework, and which layers are expected.
- Report format for volumetrics or inspection findings.
If nobody on your side can answer these, that is fine — it just means the conversation should happen with your provider rather than being assumed.
How UAV Imaging handles it
We scope deliverables before the flight, not after, because the deliverable list changes how the survey is flown — ground control, overlap, altitude and sensor choice all follow from what has to come out the other end.
If you tell us the downstream software and who is consuming the files, we will match the formats to it. And if a deliverable you have asked for is not achievable on your site — a true bare-earth model under heavy canopy, for instance — we would rather say so during scoping than hand you something that does not do the job.