Mapping & survey

Drone LiDAR for ground you cannot see

LiDAR measures distance with laser pulses, so it finds the ground between branches where a camera only sees leaves. Here is when it earns its place and when photos are enough.

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How it works

Laser pulses, multiple returns, a precise trajectory

A LiDAR sensor fires hundreds of thousands of laser pulses per second and times each one's return. Combine that range with the sensor's exact position and orientation, from GNSS and an inertial measurement unit, and every return becomes a point in 3D.

Many pulses hit a leaf, a branch and the ground in turn. The sensor records multiple returns from a single pulse, so some energy reaches the forest floor through gaps in the canopy. After flight, software classifies points into ground, vegetation, buildings and noise. The ground class becomes a bare-earth terrain model even on a treed lot.

LiDAR does not see through solid leaves; it sees through gaps. Dense evergreen stands, thick undergrowth and salal return fewer ground points, and the terrain there is interpolated. Leaf-off seasons help on deciduous sites. Accuracy depends on the trajectory, which is why the GNSS base, calibration and checkpoints matter as much as the sensor. See accuracy.

Point density is the number to agree before flying. Tens of points per square metre is plenty for terrain on open ground; mapping wires, small structures or ground under dense cover calls for more, which means lower, slower or overlapping flight lines. More density means larger files and longer processing, so ask for what the design actually uses. Classification standards follow the ASPRS LAS specification, so ground, vegetation and building classes mean the same thing in every package that opens the file.

Laser pulses, multiple returns, a precise trajectory: Illustration

Choosing the method

LiDAR or photogrammetry?

Situation	Photogrammetry	LiDAR
Open ground, gravel pads, stockpiles	Very good and usually the economical choice	Works, rarely needed
Forested or brushy lots	Maps the canopy, not the ground	Finds ground through gaps; the usual choice
Power lines, thin wires, poles	Often missed or broken	Captures wires as points
Visual record, orthomosaic, colour mesh	The strength of the method	Needs a camera alongside for colour
Low light, uniform surfaces	Struggles without texture and light	Less dependent on texture or daylight
Water	Unreliable	Also unreliable; most lasers used on drones do not map under water
Cost drivers	Lighter aircraft, simpler workflow	Heavier sensor, trajectory processing, classification time

Where LiDAR pays

Jobs that usually call for it

Treed residential and subdivision lots in coastal BC where the design team needs real ground under second growth. See land development.
Corridors: roads, trails, pipelines and power lines, including conductor positions and clearances. See telecom and utilities.
Steep, vegetated slopes for drainage, geotechnical review and retaining-wall layout.
Complex structures and as-builts where dense, even point coverage matters. See as-builts and digital twins.
Early-morning or low-contrast sites where photo texture is poor.

What goes wrong

LiDAR mistakes that cost a re-fly

Ground that is not ground

Automatic classification can call low shrubs, stumps or slash piles ground, lifting the terrain.

How we handle itClassification is reviewed by hand in problem areas and flagged in the report. →

Strips that do not line up

Poor trajectory or calibration shows as doubled roofs and stepped ground between flight lines.

How we handle itCross-strip checks and a GNSS base logged for the whole flight, with checkpoints on open ground. →

Too sparse under canopy

Flying too high or fast leaves few ground points in dense stands.

How we handle itLower, slower lines with more overlap over the densest areas, planned from the site walk. →

Point cloud nobody can open

Billions of points in one file choke a laptop.

How we handle itTiled LAZ, a thinned version for design, and derived surfaces and contours for people who do not need the cloud. →

The people around the job

Who uses a LiDAR dataset

Surveyor

They need from you: Raw and classified LAS, trajectory quality, control and checkpoint results.
You need from them: Site control and their standards for classification and density.
On the DroneLink record: All files in the site's project record, with version history if a class is revised.

Geotechnical or civil engineer

They need from you: A reliable bare-earth surface and breaklines on slopes.
You need from them: The areas of concern and the contour interval they design to.
On the DroneLink record: A LandXML or GeoTIFF surface plus contours, delivered by link.

Arborist or environmental consultant

They need from you: Canopy heights and tree locations near proposed works.
You need from them: Protected-tree and setback requirements that affect flight lines.
On the DroneLink record: Vegetation classes kept in the LAS, with a canopy height model on request.

The workflow

How a LiDAR job runs

Scope density and classes

Agree point density, classes needed and the surfaces to derive.

Set control and base

A GNSS base or correction service for the trajectory, plus checkpoints on hard, open ground.

Fly

Planned lines with overlap and cross-strips, at a height and speed matched to the vegetation.

Process and classify

Trajectory, strip alignment, classification, then manual review.

Deliver

LAS/LAZ, bare-earth and surface models, contours and a report of method and checks.

Questions

Can drone LiDAR see through trees?

It sees through the gaps between leaves and branches, not through solid foliage. Some pulses reach the ground and are classified as ground; in very dense evergreen stands there are fewer, and the surface is interpolated between them.

Is LiDAR more accurate than photogrammetry?

Not automatically. On open ground with good control, both can reach similar accuracy. LiDAR's advantage is seeing ground under vegetation and thin objects like wires; photogrammetry's is colour, texture and a detailed orthomosaic.

What file format is a LiDAR point cloud?

The standard is LAS, with LAZ as its compressed version. Both open in GIS, civil and point cloud software, including ArcGIS, QGIS and AutoCAD-based tools. Derived surfaces come as GeoTIFF or LandXML and contours as DXF.

Does drone LiDAR also produce an image?

The laser gives geometry and intensity, not a true colour photo. Most drone LiDAR systems carry a camera to colourize points, and we can fly a photo mission for an orthomosaic at the same visit.

Why is LiDAR more expensive than photogrammetry?

The sensor and aircraft are heavier and costlier, the trajectory needs careful GNSS work, and classification takes skilled review time. We explain cost drivers at scoping and quote each job; we do not publish prices.

Can LiDAR map water or under water?

Most drone LiDAR sensors do not map below the surface, and water returns are often weak or missing. Shorelines are captured; bathymetry needs other methods.

When is the best season for LiDAR?

Leaf-off months help on deciduous sites because more pulses reach the ground. Coastal evergreen forest changes little by season, so weather and schedule usually decide.

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