The Importance of Architectural Experience for Scan to BIM Modeling
The benefits of Scan to BIM are widely acknowledged in the construction industry for improving transparency, communication and reliability while developing a BIM model for an existing building. Though the process of Scan to BIM, especially with Revit 3D modelling, makes project alterations easier and contributes to faster decision making and cuts cost, architectural experience and expertise are important to make it effective. To better understand the value of architectural experience, it is equally vital to understand what scan to BIM is and how it works. So, what is Scan to BIM? Essentially, Scan to BIM refers to the process of using data collected through 3D lasers scanning a physical space, building or site to develop that data into a point cloud with millions of data points. This information is subsequently converted into a Building Information Model (BIM) in Revit, a digital representation that can be used to design, assess progress or consider options in the project. Generally, existing buildings rarely have a pre-existing BIM model. Creating a BIM model, therefore, involves using as-built drawings and documents of operation and maintenance. These also may not be available. In such cases, a BIM model can be created by scanning the geometries of building elements with advanced laser scanners. The elements are equipped with information regarding their properties, and this information is used to create a BIM family object. The Scan to BIM workflow accurately and reliably automates this process, saving time and cost in creating the BIM model. How does this happen? The spatial details of a structure or space are scanned and point clouds are formed. Cameras and radio frequency identifications (RFID) can record the structure’s data, such as material and price. Point clouds are registered in a coordinate system and a single point cloud is created. This cloud is divided into sections and information is added to surfaces/volumes. More details are added, element attributes and relationships are endowed with increased detail and a BIM model is formed. The process can be related briefly as follows: o Revit is used to include point cloud data o Scanned data is converted into effective file formats o Scanned data is converted into point cloud files with Autodesk ReCap, during the indexing process o Scanned data is converted into .rcp (Reality Capture Project files) and .rcs (Reality Capture Scan files) file formats o After selecting point cloud files, relevant files are chosen to be linked A variety of techniques capture different types of data. With an image-based technique, colours of objects are captured spatially. The range-based technique collects spatial information based on reflection. Though expensive equipment is required and difficulties exist in accurately capturing transparent and reflective objects, the range-based technique is a current favourite. Using this technique, extra effort is required to acquire information, recognise them as BIM objects and convert them to the BIM family. The popularity of laser scanning led software providers to create software that recognises surfaces within the point cloud and converts them to BIM objects. Survey data and images use a range of software tools to create precise architectural models that portray the building’s current state. Information for a range of building elements, from wall surfaces, windows, pipes to HVAC equipment is captured by laser scanning. The LOD of captured data is improved to elevate the quality of the BIM model. Point cloud to BIM services create models with a high degree of accuracy for as-built purposes and retrofit, renovation and refurbishment projects. Alternate technology, such as radars, radiography, magnetic particle inspection, sonars or electromagnetic waves are being integrated to add data regarding invisible objects, such as structural elements, beams, columns, ceilings, internal walls and external landscape elements, to the BIM model. Once the data is captured, it is then processed. Data is processed to prepare it for further use based on requirements, such as segmenting of building elements, defining meshes or recognising an object to export it to the BIM family. What happens with the data: Registration – Captured data from different scanning stations are incorporated into a single coordinate system, using Trimble Realworks or Autodesk ReCap. Create Point Cloud – After registration, data is included in a single file, the point cloud. Integration of Data – Two captured, registered data are linked by choosing 3 common points from each station. This process is repeated to integrate files with stations and all stations into a single file. This process, though slow and labour intensive, is significantly accurate. Clean Point Cloud – Irrelevant captured data, called ‘noise’, is removed from the point cloud. Noise could involve people, passing or parked cars, reflections, etc. The Scan to BIM procedure builds accuracy and detail. It follows a basic 5-step process, which can be looked at in further detail: • Survey • Laser Scanning • Process • Model • Information Survey: A project manager collates information, manages access to the site, considers health and safety requirements and assigns a site team with appropriate equipment. Surveyors select where to place survey control, and while using a total station, control points are surveyed into a closed traverse. 3D survey control markers are coordinated on site. This sets scan tolerances, and accuracies are constantly tracked. Laser Scanning: Laser scanners can be attached to standard tripods. Most scanners, such as Trimble TX8 scanners, are lightweight and have conveniently portable cases. The scanners are integrated with 3D survey control markers and supported by robotic total station control networks to collect spatial data on site. Lasers rotate at high speeds, and as the laser beam falls on different objects, an individual position with relation to the scanner and other site elements is recorded as digital data, known as a ‘point’. Several points collected together begin to create an accurate 3D representation of the space scanned. Large collections of points are ‘point clouds’. Greater number of points collected lead to greater accuracy in the scan – or ‘resolution’ of the scan. Laser scans can collect data on a million separate points in one second, which means a 5-minute scan can create 300 million points. Thus, high volumes of data can be collected in short intervals of time. More scans can be conducted, and survey information can be delivered rapidly to project teams. Laser scanners pose no risk to people, animals or existing building materials, an important consideration while working on heritage sites. High-resolution cameras on scanners can take images of the site simultaneously with the laser scan. The images then enable the ‘colourising’ of scanned data, which allows realistic rendering. Process: Spatial data is downloaded at regular intervals, processed, cleaned and then collated and compared to survey control, thus ensuring precision and the highlighting of any clashes. Importing, adjusting and preparing raw scanned data for use by a project team requires special skills, and it is necessary to commission qualified personnel to execute this process. Model: After the data has been checked and confirmed, it is sent to the modelling team, where the models are reviewed. Parameters are set by the point data, which provides an accurate representation of the structure for the high-accuracy model to be created. A single unified point cloud is then converted to a compatible format for a 3D modelling software package, such as ArchiCAD and Autodesk Revit. Generally, the point cloud to Revit model conversion is more popular. Information: The model is supplied with data required by the client, from basic dimensional information to detailed data. Embedded information includes construction materials, conditions and cost. Changes in architectural drawings are depicted in the models. For example, false ceilings and other elements have attached data that enhance the available information. The Scan to BIM process thus caters to a physical 3D representation and generates meshed surfaces. These points can be a guide to model BIM components to replicate walls, doors and windows. The requisite training, experience and additional software tools are required to execute this process accurately. Why Use Scan to BIM? Mainly, the Scan to BIM process, with cloud point scan or 3D laser survey, is a boon to renovate or refurbish existing buildings. It is relatively easy to import cloud scan files to Revit or other BIM software, creating detailed BIM models. The dimensions are then imported directly, making the process of BIM modelling easier. Scan to BIM services have been significantly relevant in the renovation of old structures and have shown proven results in refurbished schools, colleges, hospitals, heritage sites and museums, among others. The Scan to BIM workflow remodels existing elements and enables the modelling of fresh elements along with existing ones. Several factors are taken into consideration, such as quantities, material use, time duration and manpower cost. As energy-efficient buildings are in greater demand, documentation must be gathered on existing construction sites. Designs for renovation of buildings that no longer meet energy requirements for improved energy performance or living comfort require this documentation. In most cases, such documentation is outdated or missing. Advanced scanning methods, such as BIM laser scanning, are needed to register and analyse the documentation that has been created. Making a precise 3D digital model of an existing structure in a short time empowers the project team to be well informed in order to develop new designs, monitor work and verify progress. Scan to BIM services are used by retailers, contractors and architects to analyse the differences between point cloud and Revit model geometry. As-built BIM models created through the process is also relevant for large-scale architectural projects, such as tunnels and bridges. Dealing with architectural projects means that architectural knowhow and experience is of paramount importance for Scan to BIM projects. Some of the skills required for Scan to BIM for architectural services are: o Expertise in creating Revit models o Experience with point cloud data or laser scanning o Experience with topographical surveys in Revit o Expertise in creating 2D CAD (Computer Aided Design) drawings from survey data o Experience in the overall development of BIM protocols and systems o Qualifications in construction-related disciplines, primarily architecture o Sound understanding of construction techniques, survey systems and methods Architectural professionals are responsible for working drawings, schedules and specifications, as well as working on site surveys, understanding and adhering to building codes for different regions, fire safety certification, planning applications, specification writing and CAD management. Architectural graphics and model-making are also areas of expertise that professionals in the architectural field specialise in and which are essential for the process of Scan to BIM. Architectural work experience equips practitioners with the architectural aptitude, ability to think in three dimensions and the ability to work to tight deadlines as part of a team so that projects are completed via appropriate software and collaboration. Architects, engineers and contractors need to work with effective planning, coordination and sharing of project information. Stakeholders in the project must have experience with architectural processes to use intelligent building models to perform simulations and assure compliance with energy requirements and other regulations. Although the Scan to BIM procedure allows significant flexibility, a constructive understanding of client expectations is also important. Revit survey models illustrate various levels of maturity that can best be understood by those with architectural experience. The levels represented are as follows: Level 1: o Structural walls o Partition walls o Structural floors o Structural soffits (undersides of architectural structures - arches, balconies, overhanging eaves) Level 2: o All of the Level 1 elements o Curtain walling o Ceilings o Windows o Doors o Stairs/ramps o Roofs Level 3: o Level 1 and 2 elements o Sanitary fittings o Sinks o Skylights Level 4: o Level 1, 2 and 3 elements o Surface finishes o Construction materials o Fixed furniture o External ground model The Revit environment for BIM models contains extensive data defined by the client. This information allows the quantification of any element, such as room areas or costs of materials. Architects provide full designs and specifications for a project, as well as acquire planning permissions and obtain statutory consents. A well-coordinated team of architects and certified scan technicians can effectively execute high-quality as-built surveys using Scan to BIM services by capturing and interpreting the 3D scan data. Ultimately, the value of architectural experience for Scan to BIM modelling is significant to delivering high quality service to clients. An architectural understanding of the importance of individual building elements and how they integrate on a wider scale ensures relevant alterations, more informed decision-making, lower costs and faster project execution.
