Tips & Tricks

Working with surveying and pointclouds...

BIM Equity and LE34 have jointly delivered registration, surveying and 3D modeling of the BIM project used or the renovation of Lindegaarden - a four-lined, thatched half-timbered farmhosue from 1789. The building is currently being renovated by architect Stein Hagen for the Bondebylauget (The Village Council) in Lyngby North of Copenhagen.

LE34 is Denmark's largest provider of surveying and land management services. They have combined traditional terrestrial laser scanners with hand-held scanners using the so-called SLAM technology, which makes it possible to create a giant cloud of measurement points (a "pointcloud") simply by walking around the building. SLAM technology is not as precise as terrestrial scanners, but results in a shorter survey time if you can accept tolerances of 4–8 centimeters.

In addition to laser scanning LE34 has also performed photogrammetry measurements by using drones, remote-controlled "helicopters", that take thousands of photos and convert them into measurement points in a pointcloud. This type of surveying has a tolerance of 1.50 centimeters and makes it possible to survey roofs, facades and entire urban areas that would otherwise be indescribably expensive with other surveying methods.

LE34 has provided 4 pointcloud files to the project: one drone survey of the entire local area, one section of the same survey which includes only the exterior of the building, a SLAM survey of the interior for modeling of room and roof constructions, and finally a very accurate terrestrial scan of parts of the raft construction where deflection was necessary document. Below is the pointcloud of the urban area inserted in ARCHICAD for modeling of surrounding buildings as volumes.

Pointclouds or a dot cloud is exactly what the name suggests: a wealth of small dots of the same color as the material they are targeting. It looks a bit like a 3D photo, but can have some holes if it hasn’t been possible to get all the way around the object being surveyed. Thus, a tree or a column can shadow for the underlying area, which is seen when the model is rotated. With SLAM technology there is no color on the points, which actually makes it considerably harder and slightly more expensive when the pointclouds are converted into 3D model and BIM objects.

Above is a floor plan that has the facade model's pointcloud mounted upong it. It’s very clear see how the house is located within a few centimeters tolerance precision. However, it’s important to understand that the pointcloud cannot separate what is trees, grass, cars, walls, roofs, windows and doors. It’s therefore necessary to create the 3D model with the right BIM elements to get the benefits of sketching and designing in BIM. It can only be done manually, and it has been BIM Equity's responsibility to model the entire building's exterior and interior in ARCHICAD.

This means that the architect doesn’t have to spend time mounting pointclouds in the BIM program and modeling after the registration is done, which is a more complex and time consuming task than one imagines. One of the challenges is that the 4 pointcloud files take up more than 5 GB in total, which of course makes the model very heavy to work with - no matter how powerful a computer you have. Below is an example of the 3D model in the BIM program, along with the pointcloud.

When the BIM project is delivered you can always "turn" the 4 pointclouds that are linked to the project on with Xref's in AutoCAD. This means that you can always find the necessary details later in the process if you, for example, want to detail something that is not in the delivered model. On newer surveys, LE34 use a special Navvis technology, which does indoor and outdoor measurements from a small wagon, which is pushed around the building or along the facade. The precision is higher than with SLAM technology, 2-3 cm and in colour. At the same time, you get a photo-viewer, which is confusingly reminiscent of Google Street View, but from within your building! - This makes it much easier to understand the details of the building which makes it suitable to use for BIM design.

The combination of LE34's expertise in surveying - across diverse methods and technologies - and BIM Equity's experience in 3D modeling and BIM, as well as in-depth and well-defined quality assurance methods, enables ready-made BIM projects to be delivered at a meaningful price virtually all renovation projects. We can deliver in both Revit, ARCHICAD and IFC files, and it pays to have a good basis for both sketching and design.

Pro tip: When the LE34 conduct the survey, they have the option of placing points or anchors on surrounding buildings, which can later be used to place new building parts very precisly according to the coordinates of the 3D model. The points can be established as references to building parts or as fixed pegs. It creates a real-world transition to 2D drawings, 3D models, volumes, bills, and information, and back to the real world.

With ongoing 3D scans during execution, invaluable "as built" material is ensured, which accurately reproduces what, where and how it’s being built. It’s a strong alternative to the "samples" from supervision, which the a majority of advisors base their "as built" drawings on today. A good "as-built" model is the perfect basis for a BIM-based operating system and the possibility to lend precise and correct material to the advisors on future renovations or remodeling projects. In this way, the circle closes.

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About Thomas Graabæk

Thomas Graabæk has been working 10 years as an architect, with a clear interest in the digital tools used for sketching and detailing, but also with 3D modeling and visualization. Since 2006 he has been working as a BIM Manager, and his main focus has been BIM in general and particularly OpenBIM, trying to bridge collaboration between disciplines and software platforms.
  • Denmark