Scan-to-Revit Workflow: Point Cloud to Model, Step by Step

Scan-to-Revit is the sequence that turns an existing building into a Revit model: the building is laser scanned, the scans are registered into one point cloud, the cloud is linked into Revit, and the model is built against it element by element, so a wall in the model stands where the wall stands in the building. This guide walks through that sequence step by step, from the first station to the delivered file, with what each step produces, where the accuracy is set and where it is lost, and what the design team gets at the end. It is written for the architect, the engineer and the owner who orders the model, and for the team that models from a cloud itself.

1. the scan
2. registration
3. the cloud goes into Revit
4. modeling to the cloud
5. the check and the delivery

Step 1: the scan

Everything in the model is traced from the cloud, so the scan sets the ceiling for the model’s accuracy, and nothing downstream raises it. The instrument is a terrestrial scanner of the Trimble X7 class, which by its datasheet measures up to 500,000 points a second with a 3D point accuracy of 2.4 mm at 10 m and 3.5 mm at 20 m (one standard deviation), levels itself to survey grade and calibrates itself in 25 seconds. Moved on a tripod from station to station, it spends a few minutes at each; its datasheet lists point spacings of 11, 5 and 4 mm at 10 m in the standard modes, and the spacing is picked for the project: finer where ornament or millwork has to be drawn, coarser where a massing model is the goal.

The scanner measures only what it sees from where it stands, so the station plan is the scope: every room, closet, shaft and stair that has to appear in the model needs a station with a view of it; a house takes a few dozen stations and a commercial floor more. Systems above a closed ceiling are recorded only where tiles are lifted or the ceiling is open, and the scope says which. The 3D laser scanning page covers the planning, and the site preparation guide what to settle before the visit.

Step 2: registration

Each station is a cloud in its own coordinates. Registration aligns them into one, and it is where the second part of the accuracy budget is spent. With a scanner of this class the stations are registered to each other in the field, scan to scan, with no targets on the walls, and the registration report described in the datasheet lists the average error of each station and the overlap between scans. The registration is checked before we leave the site, so a station that does not close, or a corner no station saw, is rescanned the same day rather than on a second visit. The report comes with the cloud, and it is what tells the modeler, and the owner, how well the cloud holds together; a cloud delivered without one is unverified until its overlap is checked again, which the guide to registered vs unregistered point clouds explains.

People, vehicles and stray points are removed, mirror reflections behind the mirror plane are removed, and the cloud is colored from the scanner’s cameras. The registered cloud is delivered in E57, the ASTM exchange format for 3D imaging data, which carries the points with their color and intensity and the station images, and in RCP/RCS for Revit.

Step 3: the cloud goes into Revit

Revit links a point cloud only as an indexed RCP or RCS file, by Autodesk’s own help, so a raw E57, LAS or PTS file is indexed first; we do it in Autodesk ReCap. The RCP is linked into the Revit project on shared coordinates, so the model and the scan stay aligned when the file goes to the design team, and the structural and MEP models line up with it when they use the same shared coordinates. When the project has survey control, the cloud is tied to the surveyor’s points first and the model sits in the project’s coordinate system; when it has none, the cloud is delivered in a local system with the origin and the orientation documented, which is all most renovations need.

In the model, the cloud is worked in thin slices. A slice a few hundred millimeters thick at wall height, set with the section box or the view range, shows the wall faces as bands of points that are traced in plan; a vertical slice through a facade shows the window heads and sills in section; the elevation of a floor is read from a slice at the slab. Coloring the cloud by elevation shows a floor’s slope at a glance, and coloring by intensity, the strength of each return, often separates surfaces that look alike in a photograph, which helps when a duct is traced against a cluttered plenum.

Step 4: modeling to the cloud

The model is built element by element against the points, at the level of development the scope names. Scan-to-BIM scopes usually cite the BIMForum Level of Development Specification: at LOD 200 an element is “generically and graphically represented within the Model with approximate quantity, size, shape, location, and orientation”; at LOD 300 it is represented “such that its quantity, size, shape, location, and orientation can be measured”; LOD 350 adds its “interfaces with adjacent or dependent Model Elements”, the level the specification intends for construction-level coordination. LOD 300 is the usual order, LOD 200 a massing or feasibility model, and LOD 350 the elements that new work has to meet. The ceiling and plenum guide shows the levels on real elements.

Walls are placed on the traced wall faces at their measured thickness, and openings are sized to the opening as measured in the cloud rather than to a nominal dimension; a door in an old building is rarely the size the schedule says. Floors are set at their measured elevation, and a floor that sags or a wall that leans is still modeled as one plane. Columns and beams are sized to their cloud cross-section; steel under spray fireproofing is measured at the outside of the coating, and the scope says whether the model carries that envelope. Ducts, pipes and conduit are traced along their centerlines at their measured diameters where the cloud resolves them; a small pipe in a tight bundle may not return enough separate points to measure, and it is marked in the model as unverified. Equipment is modeled as objects of the right size in the right place, from the manufacturer’s family where one exists and matches the cloud. The MEP BIM page covers the systems scope.

Step 5: the check and the delivery

Before delivery the model is checked against the cloud: the modeled surfaces are compared with the points they were built from, and elements that sit outside the Level of Accuracy named in the quote are corrected. The U.S. Institute of Building Documentation’s Level of Accuracy guide states each level as a standard deviation at the 95 percent confidence level (two sigma): LOA30 is a deviation between 15 mm and 5 mm, LOA40 between 5 mm and 1 mm. A typical scan-to-BIM model from us is represented at LOA30, and the quote names the level with the LOD; the level of development says how far an element is developed, the level of accuracy how close it is to the building, and a model needs both stated.

The delivery is the Revit file in the version your office works in, with the registered point cloud in E57 and RCP/RCS, the registration report and the station images. When the team does not use Revit, the model goes out as IFC, the open standard ISO 16739-1:2024, or as an ArchiCAD file. Plans, sections and elevations are cut from the model when drawings are needed as well. The scan-to-BIM page describes the whole scope.

Price and time

What a scan-to-Revit project costs depends on the floor area, the LOD and which parts of the building are modeled. Our typical ranges: a house or an apartment, scanned and modeled, $2,000 to $4,500; interiors with the facades and the site, $2,500 to $5,000; an office or a commercial floor, $3,000 to $9,000; large buildings from $12,000, quoted on their own. The point cloud alone starts at about $1,200, and a model built from a point cloud you already have is quoted on that cloud. The exact price comes in a quote within one business day of your sending the address, the LOD and the element categories you need; the guide to scan-to-BIM cost explains what moves it. The scan is scheduled as soon as the project needs it, often within days of the order, and usually takes a day for a house or a floor; the model usually follows in two to three weeks for a house and in four to eight weeks for a commercial floor or a whole building. We scan in all 50 states.

Sources

• Trimble X7 3D laser scanning system datasheet: scan speed, 3D point accuracy, self-leveling and calibration, point spacing, field registration and the registration report.
• Autodesk Revit help: linked point clouds require indexed RCP or RCS files
• BIMForum, Level of Development Specification 2023, Part I: the LOD 200, 300 and 350 definitions.
• USIBD Document C120, Level of Accuracy Specification Guide, version 2.0 (2016): the LOA levels and the measured and represented accuracy definitions.
• buildingSMART, Industry Foundation Classes (IFC): an introduction: ISO 16739-1:2024.
• ASTM E2807, Standard Specification for 3D Imaging Data Exchange: the E57 file format.