Many AEC projects are on existing site-features or brownfield in nature. Projects beginning with inspection and documentation of on-site conditions consume more time, money and energy. While BIM can automate the new construction work, how can it be used for documenting existing buildings?
Scan to BIM process captures high-resolution 3D simulations of existing built and natural environments and converts them into workable models. Laser Scanning technology can be used to automate the conventional and tedious task of existing site documentation.
The scanners are placed at different positions to capture the physical forms on-site. The scans are then processed into 3D models called ‘Point Clouds’, which are later transformed into architectural drawings. How does this process work exactly?
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The scanner on site shoots laser beams at ‘points’
‘Points’ in a laser scanner are nothing but the recognition spots on the existing structure, made by the scanner. Scanners are capable of marking millions of such ‘points’, which are primarily data units. These units are stitched together to make a 3D visual. This is called the ‘Point Cloud’, signifying the collection of points as a 3D model.
The point cloud may look pixelated at parts, and only an x-ray version of the existing structure is formed. By using the option to colorize, the scanner captures the site as a realistic depiction. Finally, an as-built simulation model with accurate life-size dimensions are created.
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The point-cloud from the scanner is transferred as a file
3D files from the scanner are compatible only on point cloud software such as Trimble RealWorks. The point-cloud software allows us to slice the 3D model according to the kind of drawings we want- plans at different levels, sections, etc.
The point-cloud can later be imported into BIM software, where it is transformed into the final model with BIM objects like doors, windows, etc. We can detail out the objects in ways we want to. Having said these, here are some guidelines to be mindful of before documenting with the scanners:
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1. Be clear on the purpose of scanning
Higher resolution scans are usually for large scale sites to trace them accurately, in which case files become heavy and complex. Sometimes, smaller sites are better documented manually, as Scan to BIM may complicate the process incurring unnecessary charges.
Likewise, outline precisely the required areas to be scanned for efficient usage of the scanner and time. Don’t over scan. Pre-determining the LOD required, building parts and non-geometric attributes to scan gives a better direction.
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2. Scan quality and on-site positions
Depending upon how much the scanners can rotate, mark their positions on site in sequence. One scanner shot (line of sight) doesn’t capture the whole as-built and multiple scans need to be stitched. Ensure that required point-density, resolution and related properties in the scanner are set right.
3. Send the team prepared
The team should have awareness of the objectives and scanning methods, and avoid revisions. ‘Scan to BIM’ is primarily formulated to capture complex sites in a single visit.
4. Extracting the point clouds and construction of models
Make sure the point-clouds are saved in flash drives or shared on cloud servers for easy accessibility. The BIM team will then convert the point cloud into BIM models and detail them, completing the documentation.
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Benefits of scan to BIM:
- Saves time, energy and cost of documenting existing site conditions.
- Increases clarity of on-site structures and helps avoid clashes with the proposals.
- Provides transparent access to accurate data of on-site conditions for everyone.
- Provides in-built tools to make BIM objects like doors, walls, etc., within the point cloud.
- Scan to BIM is also used by contractors in new projects to scan as the construction takes place, to inform various stakeholders and avoid clashes.
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