Mapping & survey

Record what was actually built

Drawings show what was designed. An as-built capture shows what is there: roofs, grades, services, site works and exterior geometry, measured and dated, as a base for BIM and facility records.

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The problem

The drawings stop being true on day one

Every project changes in the field. A drain moves to miss a footing, a parapet rises, a retaining wall follows the rock instead of the line. Some changes reach the record drawings. Many do not. Ten years later a facility manager plans a roof replacement or a new service connection from drawings that were never quite right.

An as-built capture measures the real thing. A drone flies the site and the building exterior, collecting overlapping photos for photogrammetry or laser returns for LiDAR. Processing, done in-house, produces a georeferenced point cloud, a textured 3D mesh, an orthomosaic and elevation models. Those are delivered by link as LAS or LAZ, OBJ, GeoTIFF and DXF, which open in CAD, GIS and BIM software.

A drone covers roofs, facades, grounds and site works well. It does not see inside walls or ceilings. Interiors are usually captured with terrestrial laser scanning or a 3D virtual tour camera, and the two datasets can be registered together.

The drawings stop being true on day one: Illustration

The vocabulary

As-built, point cloud, BIM, digital twin

Term	What it is	What it is not
As-built capture	Measured data of existing conditions on a date.	A drawing set. Someone still has to draft or model from it.
Point cloud	Millions of measured 3D points, often coloured, in LAS or LAZ.	A model with walls, doors and objects.
3D mesh	A textured surface that looks like the building.	Measurable to engineering tolerance everywhere; check the accuracy report.
BIM model	Objects with properties (a wall, a pump, a door) built in modelling software.	Something a drone produces automatically.
IFC	The open, vendor-neutral BIM exchange format published by buildingSMART and standardized as ISO 16739.	A capture format. Models are exported to IFC after modelling.
Digital twin	A model linked to live or regularly updated data about the asset.	A one-time scan, however detailed.

How the work is done

From flight to model

Define the use

Roof replacement, site services, facade retrofit, insurance record or handover? The use sets the accuracy, the level of detail and whether you need LiDAR.

Tie to control

Use the project's survey control or building grid so the capture lines up with drawings and future flights. See accuracy.

Capture

Nadir grids for roofs and site, oblique orbits and facade passes for walls and details. Near occupied buildings the flight plan respects people, privacy and the site's rules.

Process and check

Point cloud, mesh and ortho are produced and checked against independent points. The report states how they compare.

Model and hand over

Your BIM team or modelling consultant builds objects from the point cloud to the level of detail you specify, then exports to IFC or your native format for the owner.

What goes wrong

Where as-built projects fail

No stated level of detail

The owner expected every downspout; the modeller delivered walls and roof planes.

How we handle itWrite the level of detail and the object list into the scope before capture. →

Data in its own coordinate system

The capture floats in local coordinates and will not line up with the survey or the next flight.

How we handle itTie every capture to project control and record the datum on the project record. →

Files nobody can find

The scan was delivered on a drive that left with the contractor.

How we handle itFiles stay on the DroneLink project record with the flight date, method notes and reports, and the owner keeps access. →

Twin that goes stale

A model built once and never updated is out of date after the first renovation.

How we handle itPlan periodic re-capture of the parts that change: roofs, site works, additions. →

The people around the job

Who needs the as-built

Architect

They need from you: Existing conditions for a retrofit or addition.
You need from them: Their required level of detail and format.
On the DroneLink record: Point cloud and mesh as a base; they model what they need.

General contractor

They need from you: Proof of what was built for closeout and disputes.
You need from them: Access and the schedule of milestones to capture.
On the DroneLink record: Dated captures at milestones, kept on one project record.

Facility or property manager

They need from you: Roof areas, equipment locations, asset records.
You need from them: Their asset list and the systems they use.
On the DroneLink record: Measured roof plans, orthos and a model their team can query. See property managers.

Insurer

They need from you: A dated record of condition before a loss.
You need from them: What they will accept as evidence.
On the DroneLink record: Baseline capture stored with its date. See insurance claims.

Facility management

What owners use it for

Measured roof areas and slopes for replacement tenders.
Rooftop equipment locations and clearances.
Site services, paving, curbs and drainage as built.
Facade geometry for cladding, window and envelope work.
A baseline before renovation, and after, for records and insurance.
Handover data in open formats, so the owner is not tied to one vendor's software.

Questions

Can a drone create a BIM model?

A drone captures the data a BIM model is built from: point clouds, meshes and photos. The BIM objects themselves are modelled by people in BIM software, to a level of detail you specify.

What is scan to BIM?

Scan to BIM is modelling a building from point cloud data. The scan gives measured geometry; the modeller builds walls, roofs, openings and equipment as objects that match it.

What is the difference between a point cloud and a 3D model?

A point cloud is a set of measured points with no understanding of what they are. A 3D model, whether a mesh or a BIM model, is a surface or object built from that data.

Can a drone scan the inside of a building?

Small drones can fly indoors in some cases, but interiors are usually captured with terrestrial laser scanners or 3D tour cameras. Drones are best for roofs, facades and site.

What file format should I ask for in an as-built?

Ask for LAS or LAZ for point clouds, OBJ for meshes, GeoTIFF for orthos and DXF for linework. For finished BIM models, IFC is the open exchange standard alongside the native format.

How accurate is a drone as-built survey?

As general industry knowledge, captures with good control are typically accurate to a few centimetres on exposed surfaces, less so on glass, dark or shaded areas. The accuracy report shows how the capture compared to checkpoints.

Is a digital twin the same as a 3D scan?

No. A scan is a snapshot. A digital twin is a model linked to data that keeps it current, such as maintenance records, sensors or repeat captures.

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