Fundamentals of Building Information Modelling (BIM)

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Fundamentals of Building Information Modelling (BIM)


As a scan-to-BIM service provider, it is important we understand BIM as a whole. Hopefully this article can provide some insight into what BIM is and then in later articles we’ll explain what our services are and how they fit into the BIM process.

Building Information Modelling (BIM) is revolutionising the Architecture, Engineering and Construction industry (AEC). Construction design, collaboration, visualisation, construction interrogation, planning, costing, sustainability and more are all being streamlined by BIM methodology. Governments and stakeholders are demanding detailed BIM plans, BIM deliverables and BIM implementation throughout the life-cycle of an asset before development begins. But BIM is also used on small scale projects, for example modelling something as simple as floor tiles to check they fit, still counts as a BIM activity.

For those new to the term, BIM can be quite confusing, abstract and hard to conceptualise. Even after reading this article the reader may come away with more questions than before!. BIM is an expansive term and so working out what it actually is, does and what it’s useful for is an ongoing process even for experienced industry professionals. While this article won’t go into too much detail, it’ll try to link together the various segments that make up the activity and lay a foundation for deeper understanding in the future.

At the most basic level it’s a 3D representation of an asset with some information that goes beyond graphical geometry. 

Ultimately, BIM is constantly evolving and the use cases, benefits and potential benefits gained from implementing BIM are always changing. It’s important to keep analysing the value that BIM brings to projects and molding the BIM process to each project in a bespoke fashion. This helps to reduce under or over modelling, cost and more.

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Our scan to bim service delivers geometrically accurate models in both Revit and Archicad.

Where were we before BIM?

Traditionally, building and infrastructure designs were communicated across multiple 2D drawing sheets, documents and datasets. Engineers, architects and contractors would often work in separate data silos despite all contributing to one single product/asset. This limited collaboration and communication and resulted in inefficiencies, design errors and other inconsistencies. Any changes in one set of plans or documents may not be reflected in another set leading to clashes on a construction site, over or under supply of materials and ultimately higher costs.

An example of such a clash would be a ventilation engineer having a different set of drawings to perhaps an electrical engineer. It’s quite possible that a cable rack installed by the electrical engineer is in the way of the piping and ducting that the ventilation engineer is installing. In the past the way to check for clashes was to use tracing paper – it’s better with 2D CAD software but still problems remained.

Some of the difficulties before BIM:

  • Design and Documentation: Architects and engineers relied on 2D paper drawings or CAD (Computer-Aided Design) software for design and documentation. These drawings had to be meticulously coordinated across various disciplines, which was time-consuming and prone to errors.
  • Communication and Collaboration: Communication among project stakeholders was challenging due to the lack of a centralised platform. This often led to miscommunications, delays, and increased costs.
  • Visualisation: With 2D drawings, it was difficult for stakeholders to fully visualise a project, leading to potential misunderstandings and misinterpretations of the design intent.
  • Information Management: As projects progressed, managing and organising the vast amount of documentation and revisions became increasingly challenging, which could lead to confusion and potential errors.
  • Construction Planning: Contractors had to create detailed construction schedules and work plans based on 2D drawings, which made it difficult to identify and resolve constructability issues and conflicts between disciplines before construction began.
  • Cost Estimation: Cost estimations were primarily based on manual quantity take-offs and historical cost data, which could be time-consuming and imprecise.
  • Sustainability and Facility Management: Evaluating the environmental impact and energy efficiency of a building, as well as optimising its operations and maintenance, was challenging due to the fragmented nature of project data.

What is Building Information Modelling (BIM)?

BIM is a methodology and an activity. Effectively, BIM can be quantified as a set of processes, technologies and standards that help to manage, collaborate and visualise all of a building’s or infrastructure’s design, asset and project data at some point or throughout its lifecycle in a digital format. At the heart of this process is a 3D model in an opensource format meaning it can be shared across numerous software packages.

Crucial to the BIM process is the idea that all teams involved in the design, construction and management of buildings or infrastructure aim to work from a single source of truth where possible via a 3D geometrically accurate representation of the asset to be built or modified (single source of truth holy grail of BIM but in reality most projects are designed using a number of different 3D models).

ISO 19650 is the main document to be referred to when implementing BIM in a structured and well managed way. The definition of BIM according to ISO 19650:2019: ‘Use of a shared digital representation of a built asset to facilitate design, construction and operation processes to form a reliable basis for decisions ‘

It is not always possible or sensible to implement all of BIM’s processes, standards and technologies. This is why BIM has a number of levels (levels of BIM Maturity). These specify what level of BIM is being implemented.

How is BIM implemented?

BIM is a methodology that is made up of a number of components. Nearly all of these components can be divided up into what’s known as the ‘4 pillars of BIM’ . Without some of the key components then BIM loses value – which is fine if only a basic implementation of BIM is used. For BIM level 2 we need a comprehensive framework for managing and executing construction projects is needed.

  1. Technology: Software tools and platforms that facilitate the creating, sharing, and analysing of BIM data. This includes 3D modelling products like Revit, Archicad, BricsysBIM which can be expanded to include time (4D) and cost (5D) and facility management software such as archibus (6D).
  2. Process: Workflows and procedures used to create and manage BIM data throughout the project lifecycle. Processes for project management, quality control, and data validation. This pillar is essential for ensuring that all team members understand their roles and responsibilities which in turn ensures consistency in the quality of work and helps to reduce errors and rework, ultimately saving time and money.
  3. People: This involves skilled professionals who use BIM to design, construct and operate buildings. Also the training and education initiatives to promote adoption of BIM from a cultural point of view. Investing in people helps them to leverage BIM technology to its full potential.
  4. Policy: Standards, and guidelines that govern the use of BIM in the construction industry. This includes standards for data exchange, interoperability, and quality assurance. Data exchange will be discussed below as it’s a key component of BIM. This pillar is important as it promotes a common language and understanding of BIM principles

The number of components involved in a specific project very much depends on the size, complexity and budget of the project. For example, most small scale projects will potentially use software that facilitates BIM such as Revit, but won’t implement detailed standards and strategies regarding security and data management that will fall under the policy pillar. Large projects and all government contracts will likely ask for a BIM execution plans where roles and responsibilities are defined as per the standards ISO 19650 at the project outset.

ISO 19650 – Mainly applies to BIM level 2

ISO 19650 is the international standard that governs how BIM and all it’s components are to be implemented. It provides a framework to manage information and implement a unified approach across all BIM projects. It is based on the previous UK BIM standard document PAS 1192.

Section 3.3 from the UK bim framework guidance describes ISO 19650 as:

“The ISO 19650 series calls for transparent, collaborative cross-sector ways of working which requires mutual understanding and trust alongside appropriate/proportionate measures and processes to reduce the risk of loss, corruption or disclosure of information. This is important to maintain the safety and security of:

  • personnel and other occupants or users of the asset and its services;
  • the asset itself;
  • asset information; and/or
  • the benefits the asset exists to deliver.”

It applies mainly to BIM level 2. Ideally BIM level 2 projects apply ISO 19650 and adhere to the standardised way of working that it sets out.

Some of the work that project teams implementing BIM level 2 have to undertake and investigate:

  • OIR – Organisational information requirements
  • PIR – project information requirements
  • EIR – Exhchange information requirements
  • AIR – Asset information requirements
  • BEP – BIM execution plan
  • RM – Responsibility Matrix plan
  • MIDP – Master information delivery plans.

Not everything has to be implemented for BIM to take place and be realised. Project teams, contractors and designers are all still learning, including ourselves here at EOS Geomatics. BIM can be implemented on both a small and a large scale. You lose value if, for example, you don’t have all your contractors aligned with a BIM methodology – say, some sub contractors still design in 2D but, perhaps it doesn’t matter if it’s just a small project. This is why you have varying levels of BIM and Level of Detail (LOD). It depends on the project size, requirements and project lifecycle stage.

BIM Maturity levels and LOD Explained

BIM Maturity levels represent the level of collaboration, technology and standards to be implemented in a project. BIM level 3 isn’t currently feasible on most projects due to technology, software and workforce limitations. Level 1 is most commonly implemented and level 2 is the go to for all government contracts and other large projects. It will feature most of the components seen above in the ‘4 Pillars of BIM’.

CDE = Common data environment.

Model federation = A number of models combined into one complete federated model.

LOD – Level of detail and level of development

LOD can mean two things, level of detail and level of development. Level of detail is set out in the UK specification PAS 1192, which describes both level of detail and level of information.

Level of Development

Level of development is an American term which refers to a degree of suitability and completeness of a particular BIM element for a particular stage of the project. It takes into account both graphical and geometric accuracy as-well as information.

Level of Detail and Level of Information

Level of Detail refers a graphical representation of an element. It indicates the level of geometric complexity and detail an element has and is important for defining how accurately and intricately an object or building must be modelled/measured.

Definition according to BSI PAS 1192-2:2013:

A.77 Levels Of model Detail (LOD)
Description of graphical content of models at each of the
stages defined for example in the CIC Scope of Services.

A.78 Levels Of model Information (LOI)
Description of non-graphical content of models at each of the
stages defined for example in the CIC Scope of Services

In the later standard ISO 19650 – level of detail isn’t specified. Instead level of information needed is discussed. This is to limit the use of confusing acronyms and make sure that objects and elements aren’t over modelled just to meet an arbitrarily defined level of detail. A BIM model can have different LOD’s for different areas and over or under modelling should be prevented wherever possible.

In any case, it helps to know what Level of detail is as it allows both the client and the provider some level of clarity in terms of expectations of what a delivered product will look like.

LOD 1 – Mass model

LOD 2 – Core model

LOD 3 – Standard survey model

LOD 4 – Detailed survey model.

For example, in LOD 1 structure detail’s won’t be modelled. You’d just graphically represent the outer extents of a building. In LOD 2 you will show basic structural elements but won’t show building details such as gutters and down pipes.

A much more detailed explanation can be found here – scroll to the bottom to find useful downloadable documents.


Computers and BIM

Binary code and BIM

Because BIM revolves around digital software applications and virtual machines, all data is essentially a series of 0’s and 1’s, aka binary code. Computers have billions of transistors which can take electrical input turning them from ‘off’ to ‘on’– or from 0 to 1 (with 1 being on and 0 off).

This input is taken from electrons supplied via the power source. This is where the term binary code comes from – you have two digits to represent all digital data. We use these 2 digits to represent something based on numerical value. Because we only have 2 digits, it means that we use base 2 rather than base 10. I.E 00010 = 2 00100 = 4 and so on.

Via mapping or encoding we can assign a numerical value in binary code some meaning. I.E the letter ‘H’ will be given the value of 72 in binary code. An 8-bit ASCII file is one such form of encoding (each binary digit is one bit). A more modern one would be Unicode (16-bit or 149,000 potential characters) Because the file format for BIM interoperability was chosen in 1980’s the mapping/encoding system used is ASCII.

BIM, Computers and cross software compatibility.

One of the fundamental pillars of BIM Is cross software compatibility. A construction project will often require contractors to use at least 7 different suites of software from specialist MEP design software to generic BIM and CAD 3D modelling software. The ability to take data from all these different inputs and merge them into one BIM model is essential if BIM is to be truly collaborative.

This revolves around two file formats which sets rules on the way data is stored. STEP and IFC. Industry foundation classes (IFC) was based on the STEP file format. STEP is essentially a data model focusing on all disciplines of engineering. The IFC file format uses the same format as STEP but it’s entities are all focused and specific to AEC.

IFC Open source

Software companies usually create a proprietary data and file system for their product which can’t be used by other companies without difficulties such as data loss. This creates competitive advantage and reduces competition. But it means that data from one set of software isn’t compatible with another.

For BIM methodology to work, an open source system with all data and file format documentation being available to different companies was needed. This is why the IFC file format was created. It is known as an open data exchange format and can be used by any application independently of who developed it. Interoperable file formats allows:

  • Faster and more informed decision making
  • Better information flow
  • Less errors and therefore less problems on site
  • Limits data re-entry
  • Facilitates better communication
  • Allows for a single source of truth.

Overall, IFC plays a crucial role in BIM by facilitating interoperability, collaboration, and data exchange between different software applications. It enhances the efficiency, accuracy, and effectiveness of BIM processes, enabling better-informed decision-making and improved project outcomes.



BIM, at its core, is a digital representation of the physical and functional characteristics of a building. It goes beyond traditional 2D drawings by incorporating 3D models enriched with data and information. This information-rich environment enables stakeholders to make more informed decisions, streamline workflows, and improve overall project outcomes.

It’s a broad subject which can get bogged down in acronyms and obscure and loosely defined definitions. Hopefully this article can help to establish some basic knowledge on the subject.

For further reading these websites and articles will be useful:



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