Point Cloud to 2D/3D As-built Models for Heritage Buildings

The ability to digitize construction drawings and visualize as in conditions of renovation buildings, has given as-built drawings increasing acceptance in the construction space. Understanding how to create accurate 2D/3D drawings from point cloud scans, holds the key to successful project execution.

Conventional techniques or 2D plans for surveying complex geometries of heritage buildings can be inaccurate and time-consuming. Renovating such structures which often miss out on construction documents, as built drawings or paperwork pose serious construction challenges. Creation of Point Cloud to 2D/3D as-built models is an ideal solution to overcome this challenge.

3D laser scans of renovation constructions accurately register non-parametric geometries. Architects, engineers, contractors and surveyors apply BIM tools to convert this scanned data to 3D models. This eases up the integration of existing structures into a point cloud to BIM landscape.

What are the common renovation challenges for heritage construction?

Surveying or recording complex geometries with various elements like pillars, walls and other objects.
Relocating costly and fragile objects in the building to initiate a survey.
Frequent site surveys to cover the entire structure.
Increased rework based on incomplete drawings or record-keeping of historical buildings.

As-built models address renovation challenges

As-built models deliver a host of benefits for project teams and stakeholders. For buildings that do not have prior construction drawings or documents, 3D laser scans converted to as-built drawings help stakeholders capture exact dimensions of the area, and thereby make informed decisions regarding installations or modifying an existing structure.

For contractors, as-built drawings provide a precise record of any changes in the pre-construction stages while helping them visualize the entire project at each stage of construction. This pre-construction visualization make it easier to identify and resolve any issues or problems arising due to any deviations from the original designs.

Our scan to BIM solutions save up to 15% on construction costs.

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5 steps to create 2D/3D as-built models for heritage buildings

Creating accurate as-built models requires skilled BIM experts. To create an accurate as-built model for heritage buildings, it is important to ensure and practice the following steps.

1. Generate accurate point cloud scans

As a first step to creating a 2D/3D as-built model, ensure that the building scans are accurate. The surveyor has to make sure that all the positions are registered as the scanner usually considers only the scanned objects in the line of sight. Terrestrial scanners, hand-held scanners and drones are effective scanning tools.

2. Converting point clouds to as-built models

The next step is developing a standardized workflow to convert a point cloud to a Revit model.

Multiple scans are joined together to create a single point cloud file
Targets or survey points can be used to join the scans or scans can be overlapped by identifying similar features
Selecting ground control points is important. A minimum of five ground control points needs to be captured for software references. Greater accuracy can be achieved with a higher number of ground control points. For better results, Ground Control Points need to be scattered, rather than clustered

3. Creating as-built 2D drawings

The final deliverables are built after the registration process is completed:

2D as-built drawings can include architectural surveys or topographical surveys and may vary in the site area, dimensions, contours, elevations, etc.
Point clouds are imported into software like AutoCAD® to create such drawings.
Drawings are finalized through tracing and careful viewing and navigation of the point cloud file.

4. Modeling geometries with as-built 3D models

Heritage or historical buildings require a 3D as-built textured point cloud to Revit model.

Understanding goals and objectives with the best tools and techniques are key to accomplish modeling complex geometries.
For architectural surveys, point cloud files are imported to software like Revit® to create a point cloud to BIM model.
A macro to micro approach can be utilized to prioritize elements like floors, walls, roofs, etc.
Fixing the point cloud within a project is key to make sure the project does not rotate or move.
Within BIM workflows, family libraries need to be identified to model quicker and better.
Revit helps modelers select parametric families to enhance productivity for heritage buildings.
Identifying elements and using parametric capabilities to set dimensions helps save modeling time.
Models are created to avoid clashes and conflicts between various construction members.

5. Quality check

After all the elements are created, they are checked for elevation, section and 3D view to make sure the elements are modeled correctly and complement the point cloud.

Parameters that need to be checked are:

Check the converted as-built model by separating horizontal and vertical sections of each element.
Check the deviation between model and point cloud scans for each element so that tolerance accuracy is ensured.
Ensure accuracy of categorization filters for properties such as work set, element category, material, element function, and phasing.
Check for presence and accuracy of all the elements in plan, elevation and section view.
Check clashes between various disciplines.
Clean all reference points and detailed lines from the model.

As-built models save renovation costs and time for a heritage building in UK

Point cloud to BIM LOD 400 for a Heritage Monument Building

A laser-scanning service provider needed a Point Cloud to BIM model with LOD 400 for renovation, maintenance, and facilities management of a 16th century heritage monument.

Hitech CADD Services helped the client save on renovation time and overall construction costs by providing:

Revit BIM model with LOD 400 as per existing conditions
Accurate quantities and workforce costs
High-quality Revit Families
Well-defined QA/QC processes
Detailed documentation of the 580,000 sq. ft. area

A best practices checklist to create as-built models from scanned data

1. Choose the right equipment and methodology for scanning

Every laser scanner has its own strengths and weaknesses. Whether it is terrestrial scanners or drones, it is crucial to understand the requirements of the project and choose one that is best aligned for the job.
It is advisable to do an initial run of model checking on a small section or area and then move across entire project. The same check can also be done perpendicularly.

2. Identify information requirements before conversion

Identify and gather all the necessary information such as the building elements to be modeled, required LOD and the required non-geometric attributed to create the BIM model. It is crucial to have a clear understanding of the client requirements and needs before entering the information from the scanned data into 3D BIM models.

3. Converting scanned data to 3D models

Scanned data when inserted into software tools like Revit, generate accurate and information rich 3D BIM models in .rcp format. While converting the scanned data to 3D BIM models, it is important to simultaneously compare a delimited area, with the use of plan view, section and 3D. This ensures that the information in the BIM model matches with the scanned data as per the required LOD.

One can use the visibility settings to see the point cloud of a single contrasting color and check discrepancies faster.

4. Maintain dimensional tolerance

The modeling accuracy of a BIM model is based on the dimensional tolerances of elements according to relevant codes and regulations.

For instance, if the allowed dimensional tolerance for a given modeled element is +/-10 mm, the deviation from scanned data to the modeled element cannot exceed +/-10 mm. If the deviation exceeds the specified dimensional tolerance, it should be non-graphically mentioned in the model.

5. Perform rigorous QA/QC

A thorough quality check needs to be done to ensure proper categorization of various planes of point cloud and building elements such as the wall, floor, ceiling, etc. It is important to be able to identify minute details in the geometry of various elements and ensure that all the elements are correctly read and modeled as per BIM elements.

For instance, a floor may be modeled as a BIM element but not as an extruded solid. It needs to be placed exactly where the scanned data showed its plan and geometry.

Point cloud to BIM model reduces construction costs

A building construction company needed a coordinated and clash-free BIM model for an educational institute in UK. With point cloud scans as input, Hitech CADD Services built a 100% accurate and clash-free scan-to-BIM model with architectural and structural details, which helped the client:

Reduce construction risks
Make informed construction decisions
Lower construction costs

Read full case study →

Automation and AI will drive the future of Point Cloud to BIM

Although the adoption rate and knowledge of point cloud to BIM may be limited at present, it will definitely increase in the future. Technology like Li-Dar, robots and drones are already being used globally, with high-resolution laser scanners, cameras as well as gyroscopic stabilizers. Stakeholders gain detailed information about hard to reach areas of an existing structure or building.

With improvement in technology, the future is all about automation and AI. When real time 3D models are combined with AR/VR, a user is able to visualize a structure at the pre-construction stage and interact with it virtually. With virtual walkthroughs, stakeholders are able to make smarter and informed decisions regarding renovation of their construction projects, while saving time and construction costs.

Finally, it may be concluded,

Point cloud to 2D/3D as-built BIM modeling techniques and tools have made a significant contribution to the field of renovation and restoration of heritage buildings. The capabilities of documenting the existing state of heritage buildings through quick, non-invasive and efficient techniques enable stakeholders to gain reliable recording for an as-is condition structure.

Point cloud to BIM modeling is truly a game changer for the construction industry as far as restoration and renovation of heritage buildings is concerned.

Get 3D Revit models at +-10mm accuracy from point cloud scans.

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Tags:
as-built 2D drawingsAs-built Modelsheritage constructionPoint Cloud to 2D/3D as-built modelsPoint cloud to BIMPointCloudBIMServicesrenovation challenges

Authored by:

Harika Singh is an academician and published writer. Her passion for engineering and technology reflects in the in-depth coverage she provides on technology trends. 20 years of work association with institutes of repute across India and the US positions her to provide valuable insights to business stakeholders on achieving scalability and operational efficiencies through digitalization.

How to Create As-built Models from Point Cloud for Heritage Buildings