What each method is actually built for
Terrestrial laser scanning (TLS) is the tripod-based, stop-and-set-up method: a phase-based scanner is placed at a series of fixed positions, each one capturing a dense, static sweep of everything in range before the crew moves to the next setup. It is slow in the sense that each position takes real time to occupy, and it is the tightest, most defensible measurement of the three. This is the method behind pipe rack tie-in verification, structural steel documentation, and any scan-to-BIM model that a design or fabrication team will actually build against.
Mobile mapping — the SLAM-based, wearable or cart-mounted systems in the NavVis class — trades some of that accuracy for speed and reach. A crew walks the space continuously while the system localizes itself against the geometry it has already seen, building a point cloud as it moves rather than stopping to occupy fixed positions. A warehouse, a multi-storey building, or a long campus corridor that would take a TLS crew days to cover setup by setup can be walked in hours.
Drone photogrammetry and LiDAR are the only methods on this list that see a roof, a yard, or a site the way nobody standing on the ground can. A drone flies a planned pattern over the area, capturing overlapping imagery or direct laser range measurements, and the result is processed into an orthomosaic, a surface model, or a point cloud covering ground nothing else on this list can reach without a lift, a harness, or a very long day.
The accuracy trade-off, honestly
This is the part a lot of marketing glosses over, and it is worth being direct about it: these three methods do not deliver the same accuracy, and no amount of processing afterward changes that. Terrestrial laser scanning holds the tightest tolerance of the three, because a scanner sitting still on a tripod, tied into a surveyed control network, measures range with none of the drift a moving system has to correct for as it goes.
Mobile mapping does not match that. A SLAM system is continuously estimating its own position from the geometry around it as the operator walks, and that estimate accumulates small errors over a long walk the way any dead-reckoning process does, even with loop closures and visual-inertial correction pulling it back toward consistency. The accuracy sits a tier looser than tripod scanning — genuinely useful for layout, asset location, orientation, and whole-building coverage, and not the tier a fabrication drawing should be built from. Pretending otherwise is the kind of claim a competent buyer checks against the registration report and catches immediately.
Drone-based accuracy runs on a different axis entirely: it is driven mainly by ground sample distance and by whether the flight is tied to surveyed ground control. Flown with control points and RTK or PPK positioning, results on hard, well-lit surfaces land in a comparable working tier to mobile mapping; flown without control, the result is noticeably looser and is really only defensible for visual and relative-quantity work rather than anything tied to a coordinate system. None of the three methods is "better" in the abstract — they sit on a real accuracy ladder, and the job is to put each one where its tier actually fits the decision being made.
Comparing the three methods
No single row in this table is the universal winner — each method is built for a different part of the job.
| Terrestrial (TLS) | Mobile mapping (SLAM) | Drone (photogrammetry/LiDAR) | |
|---|---|---|---|
| Best at | Tight-tolerance interior geometry: structure, pipe, equipment | Fast, complete coverage of large or multi-level interiors | Roofs, yards, site topography, anything only visible from above |
| Accuracy tier | Tightest of the three; the reference tier for fabrication work | A tier looser than TLS; accumulates over a long continuous walk | Depends on ground sample distance and ground control quality |
| Speed / coverage | Slowest per area; each position is a discrete setup | Fastest interior coverage; continuous walk, no fixed setups | Fastest for large open or elevated areas; limited by flight time |
| Works well indoors | Yes, standard use case | Yes — does not depend on GPS, only on visible geometry | No — not a practical indoor tool |
| Works well outdoors / aerial | Only for what a tripod can reach from the ground | Limited to where a person can walk | Its native environment |
| Typical deliverable role | The accuracy anchor a model or drawing set is built against | Whole-building coverage layer, asset location, orientation | Orthomosaic, surface model, or point cloud for roof/site scope |
How site conditions actually decide it
The right method for a given job is rarely a preference — it falls out of the site itself. An occupied building where a crew cannot hold a room for the time a full TLS setup sequence requires often points toward mobile mapping for the general coverage, with terrestrial scans reserved for the specific zones that actually drive a design or fabrication decision. A tenant space that has to be handed back to daily operations by a certain hour is not the place to schedule forty TLS setups if a SLAM walk can cover the same footprint between two escorted rounds.
Indoors, GPS is not available to any of these methods for direct positioning — that is precisely why mobile mapping relies on SLAM rather than satellite positioning: it localizes against the geometry it sees, which is what lets it work reliably deep inside a building where a GPS signal never reaches. Outdoors, the opposite constraint applies to drones: flight planning has to account for controlled airspace, and a drone captures nothing indoors at all, which is why a project split between an interior fit-out and a roof condition survey is never a one-method job.
Size and access matter as much as occupancy. A single mechanical room is a TLS job — the setup count is small, and the accuracy return is worth the time. A ten-building campus, a multi-storey office tower, or a warehouse the length of several football fields changes that calculation, because the number of TLS setups needed to cover it fully grows in a way that a continuous mobile mapping walk does not. And how long a space can be held matters independently of its size: a live production line that can only be accessed in short windows favors whichever method captures the most ground per minute of access, which is often mobile mapping for the general layout and short, targeted TLS setups only where the tolerance genuinely requires it.
One job, one registered dataset
On a real project these methods are not run as separate, disconnected efforts — they are tied into a single coordinate system through a shared control network, typically set and checked with survey-grade GNSS and total station equipment, so that a terrestrial scan of a process unit, a mobile mapping walk of the surrounding building, and a drone survey of the roof and yard all land in the same registered dataset. A designer or engineer opening the combined point cloud should not be able to tell where one capture method's data ends and another's begins, except by checking the density.
The planning question, in practice, is which method covers which part of the site, not which single method wins. A typical industrial project might use terrestrial scanning in the process areas and equipment rooms where a fabrication drawing or a clash check depends on the tightest tolerance available, a mobile mapping walk through corridors, mezzanines, and secondary spaces where complete coverage matters more than the last millimetre, and a drone flight over the roof and site where nothing at ground level can see. Each dataset carries its own registration report — residuals, control network, and any area that could not be reached — so the combined deliverable is honest about which parts of it were measured to which tolerance.
That honesty is the actual deliverable, more than any single point cloud. A buyer who understands that a mobile mapping layer exists for coverage and a terrestrial layer exists for tolerance can make a real decision about where to spend the field time that a project's budget and schedule actually allow — rather than assuming one instrument did all of it to the same standard, which is the assumption that causes problems downstream when a dimension pulled from the wrong layer turns out looser than the drawing needed.
A short, honest recommendation
If the deliverable is a fabrication drawing, a clash model, or anything an engineer will build against, specify terrestrial laser scanning for those zones and do not let a lower-tier method substitute for it because it is faster or cheaper to run. If the goal is complete, fast coverage of a large or multi-level interior where the priority is knowing what is there and roughly where — layout, asset location, space planning, a remote walkdown — mobile mapping is very often the better use of field time. If any part of the scope is a roof, a yard, a stockpile, or site topography, that scope is a drone job by default, because no ground-based method reaches it without extraordinary effort. Most real projects use more than one, and the right question during scoping is not "which technology," but "which zones need which tolerance, and which of these three methods gets there."