Many people interested in laser technology wonder what 3D scanning looks like in practice and how long it takes to capture a specific object such as a building or a factory floor and how much effort it takes to evaluate the data.
In this article, we explain the workflow from the initial scan preparation to the production of deliverables using the example of a 1,200 square meter hall in the attic of a factory from the beginning 20th century.
Usually you scan an object because you have a contract to do so. To be able to make an offer, the effort it will take must be estimated. You need to get an idea of the object, with the help of paper plans, photographs, 3D visualization or ideally through a visit of the scan site.
Picture 1: FARO Sales Engineer Dirk Fichtmüller scanning a factory hall.
The Scanner Looks Around – Defining Scanner Positions
The FARO Focus laser scanner produces three-dimensional, coloured, and geometrically accurate images that look like cloudy 3D photographs, so-called point clouds. To do this, it uses a laser beam to measure one million points per second, about others distance and relative position of the points to its own location. The device turns around its axis and scans ceilings, walls, floors, in short everything that is visible from its position. What is not visible from its location is not captured, such as sides and rears of columns, window reveals and lintels, or the room and the walls behind corners. To capture these objects, the scanner’s position needs to be changed.
Look around at a possible position and remember what is visible and consider from which position the invisible sides can be seen. It is useful to make a sketch of the place and to note down possible positions.
Capturing a 1,200qm Factory Floor in Two Hours
At the factory floor, 24 scanner positions were needed. Each scan took a little more than 4 minutes, then the scanner was moved to the new position. The scanner captured everything in the room, pillars, windows, lintels, pipes, the roof slopes that could only be reached conventionally with a scaffold, unevenness in the floor, holes in the wall and in the plaster, things that could only be captured with tape measures in weeks of work or even not at all.
Get the Job Done On-Site
With FARO Scanner and SCENE Software the job is done completely on-site. After two hours the entire object was documented in a fully registered scan project. With scanners from other companies, hours of work still must be done in the office, especially for a target-based registration.
Picture 2: Point cloud of the factory floor in FARO SCENE.
Cloud-to-Cloud or Target Based – The Registration Process
This alignment of single scans against each other is called registration. The registration is a necessary, time-consuming, and computationally intensive process that can take hours depending on the project size and number of scans. With FARO the registration is done on a laptop on-site parallel to the actual scanning process. The scanner measures the points relative to its own location. After scanning, there are a lot of single scans with e. g. only two sides of pillars and areas with no points at the places that the scanner couldn’t see from its primary actual position. These single scans must be assembled to one entire project to get an overall view of the object. It’s like mounting single photographs to a panoramic image. The fully registered project covers the entire hall. It’s possible to measure the total length and width without working in a puzzle of single scans.
Floating Around – Cloud-to-Cloud
The registration process is not easy. The scans must overlap, they must contain the same objects from different views. E.g. scans made from two different positions will have different densities, as the distance of the scanner to the wall differs. As a result, the two single scans will not include exactly the same points. So, it is not possible just to bring points of the two clouds to overlay. Therefore, one pushes the point clouds into each other until most of the points on overlapping objects are as close as possible to each other. Optically until it looks sharp. This method, “Cloud to Cloud” registration, has principally an inaccuracy of several millimeters. In projects with many scans, the error can add up to centimeters.
Better Having Targets
To align single scans we use targets. The 3D scan targets are very precisely worked balls. To register two scans the software must find at least the same three balls in both scans. It knows that they are perfect balls, knows their precise position because there are many measuring points on the balls, and knows their exact center point. As a result, the positions of the same three points are known in both scans. The point clouds can be tilted and moved until the three points overlap precisely.
Saving Time, Money with On-Site Registration
The advantage is not only the time saved in the office. Much more important, especially for inexperienced users, is that they can see the current state of the entire 3D project on-site while scanning. They can realize on-site when important parts of the object have not been captured or registration fails. It happens quite often that missing parts in scans are noticed in the office and the surveyor must go back to the object so using the FARO workflow prevents expensive revisits to the object.
The Job is done – The Job begins!
If the requested deliverable of the job is the 3D scan project the job is finished upon leaving the location. This is often the case when an object must be precisely documented. But in most cases, the scan data is needed for further processing.
The factory floor, in this example, is to be renovated and rebuilt. The pure scan project is now used in the search for a future project partner, click on the link below to view the factory floor on SCENE WebShare Cloud:
As soon as a partner is found, the rebuilding and renovation planning will begin in AutoCAD® Software or Autodesk® Revit®. FARO offers industry-specific workflows, from scanning to data evaluation in AutoCAD and Revit, for Architecture, Plant Engineering and Civil Engineering, for the Oil and Gas Industry, Cladding and Padding, Interior Fitting and many more. FARO also offers Software that uses 3D scanner data for object monitoring, quality control and design layout.
3D Scan Data – Raw Data that Must Be Evaluated
Point clouds consist of millions of single points. Planners use CAD and BIM programmes. For them, not coordinates of individual points are interesting, but the fact that millions of individual points form a wall or a complicated piping system. They should be available as BIM objects in Autodesk Revit, or as pipe-runs in AutoCAD Plant 3D, so that they can continue working with these objects in their planning tools.
They want to know whether planned objects collide with existing ones, whether scanned surfaces are flat, how large tank volumes are, how far real objects deviate from planned ones. For this information they need evaluations and FARO has the appropriate software and workflows, like FARO As-Built for AutoCAD Software and FARO As-Built for Autodesk Revit. With these plugin solutions, point clouds can be evaluated quickly and easily whenever they are needed, i.g. directly in AutoCAD and Revit.
Picture 3: Point cloud with planned drywall installations in Autodesk® Revit®, using clash detection functionality.
Picture 4: Evaluation of scan project data in AutoCAD® Software.
The Entire Scan Workflow is Crucial
Often, the software is neglected when deciding which 3D scan devices or solutions to choose. But one hour of on-site scanning is followed by days of evaluation in the office. The time required and the correlation between scanning and evaluation depends, for example, on the degree of detail with which the point clouds must be evaluated.
Is the representation of scanned pillars as cuboids accurate enough or are the beveled edges of the pillars needed? Does it have to be evaluated down to millimeters or are three centimeters sufficient enough, as is often the case in architecture and construction? The choice of the right workflow decides whether a BIM model is delivered after one or three days or even after weeks.
Before we started with scanning the factory hall we captured the 2D floor plan with a FARO ScanPlan 2D Mapper. The device dramatically speeds up the creation of floor plans. Capturing the floor plan and shooting 360-degree panoramic images took less than 15 minutes for 1200 square meter. The documentation with the ScanPlan avoids a visit of the prospective customers during the tendering of surveying orders, building orders etc…
Picture 5: Plan of the factory floor with scanner positions calculated by the Scan Assist functionality of the ScanPlan.