Laser scanning · Terminology
LiDAR or laser scanning? The same physics, a different job
The two words get used interchangeably and then a specification asks for one and gets the other. The distinction is not the instrument. It is where it is standing.
LiDAR means light detection and ranging: fire a laser pulse, time the return, calculate the distance. Terrestrial laser scanning does exactly that. So does the unit on a drone. So does the sensor in a survey aircraft. At the level of physics there is no distinction to draw, and anybody insisting the terms mean different things is usually defending a product rather than a method.
What differs, and differs enormously, is the platform — and the platform decides accuracy, coverage and what the data can be used for.
Where the instrument stands
| Platform | Typically called | What it suits | Trade-off |
|---|---|---|---|
| Tripod | Terrestrial laser scanning | Buildings, plant rooms, tunnels, interiors, anything becoming a BIM model | Highest accuracy; slow, and sees only what is in line of sight from each setup |
| Drone | UAV LiDAR | Acreage, corridors, vegetated and overgrown ground | Covers ground fast and reads through canopy; less precise than a tripod |
| Vehicle or aircraft | Mobile or airborne LiDAR | Long corridors, highways, large terrain | Enormous coverage; accuracy tied to the positioning system carrying it |
A static instrument knows exactly where it is. Everything else has to work that out continuously while moving, from GNSS and an inertial unit, and every error in that solution lands in the cloud. That is the whole reason a tripod scan is more accurate than a flown one, and it is why asking for "LiDAR" without saying from where is asking for an unknown tolerance.
The canopy question
The one capability that genuinely separates LiDAR from the obvious alternative is vegetation. A laser pulse fired into a wooded site produces several returns — the canopy, the understorey, and often the ground beneath. Keep the last return and a bare-earth terrain model can be built under trees.
Photogrammetry, which builds a surface from overlapping photographs, cannot do that. It reconstructs what the camera could see, and under a canopy the camera sees leaves. On a wooded or overgrown site that difference decides whether the deliverable is a terrain model or a picture of a treetop.
Point cloud is not a drawing
A registered cloud is a measurement, not a deliverable most people can use. Turning it into something a designer builds from — modelled geometry, a 2D set, a BIM model at a stated level of development — is separate work, and it is usually the larger part of the job.
Scope it explicitly. "Scan the building" and "give me a Revit model of the building" are different commissions with different prices, and a cloud delivered against the second expectation satisfies nobody.
Why it sits with the geophysics
Scanning answers what is above ground; geophysics answers what is below. Registered into one coordinate system, a buried duct bank and the plant room over it exist in the same model, which is the only arrangement in which a clash between them gets found before it is built rather than during.
On acreage it also saves a visit. A solar site flown for terrain can be flown at the same mobilization as the magnetic survey for abandoned wells.
What to specify
Say the platform, not the acronym. Say the tolerance you need and let that choose the platform if you would rather. Say whether vegetation has to be seen through. And say what you want at the end — cloud, drawings, or a model — because that decides most of the cost and almost none of the fieldwork.