In this guest post, Marzia Bolpagni (PhD Candidate, Politecnico di Milano, Italy) provides a comprehensive review of the 'LOD' term and its many nuances from across the world. I’m sure you’ll find her insights, comparative tables and detailed charts very informative:
All practitioner who use Building Information Modelling tools and workflows in their daily practice must have already faced the ‘information exchange dilemma’. That is, to effectively deliver a project, it is first essential to define what information is needed, from whom, and at what level of detail. To meet this challenge, several international specifications have been developed to address the definition of modelled objects and information embedded within them - these include: Model Progression Specification (MPS), Model Development Specification (MDP), Level of Development, and Level of Detail. Usually, these specifications are included within a BIM Execution Plan (BEP) or a similar document. However, much confusion still surrounds these concepts due to the large number of acronyms and definitions across countries and sometimes within the same market. Thus, this post will focus on clarifying the principles, surveying historical data, differentiating between different specifications, and reflecting upon a possible future scenario.
History of ‘LOD’
In 2004, Vico Software (now part of Trimble) introduced the Model Progression Specification (MPS) concept to facilitate the management of information within BIModels. The ‘LOD' acronym was thus used for the first time to indicate ‘Level of Detail’ and to establish the progressive reliability of information over a period of time. In 2008, a similar concept was adopted by the American Institute of Architects (AIA), California Council’s Integrated Project Delivery (IPD) Task Force, and later by the AIA National Documents Committee. The AIA introduced five ‘Levels of Development’ (LOD100-LOD500) in the E202™–2008. Building Information Modeling Protocol Exhibit, which was updated in 2013. Also in 2013, the BIMForum published the Level of Development Specification based on the AIA protocols. These documents then became the point of reference of several BIM Guidelines and documents in a number of countries – including Australia, Canada, Singapore, China, Taiwan, Germany and France. Other countries developed their own variant specification. For example, in New Zealand, the LOD specification follows the AIA (2013) but defines ‘Level of Development’ (LOD) as a sum of four different aspects: ‘Level of detail’ (LOd), ‘Level of accuracy’ (LOa), ‘Level of information’ (LOi) and ‘Level of coordination’ (LOc).
In 2007, Denmark developed a different classification system based on seven ‘Information Levels’ (0-6) covering geometric and non-geometric data within virtual building elements that different parties rely upon. This concept was then incorporated into the Australian CRC National BIM Guidelines document (2009) and the ‘Nederlandse BIM informatieniveaus’ (2014), although the US Levels of Development (LOD100-LOD500) were the dominant system used in both countries.
Following that, the Hong Kong BIM Project Specification (2011) incorporated several tables for defining the minimum ‘Level of Detail’ required with models but without providing a classification.
Figure 1: The History of ‘LOD’ (Updated July 22, 2016 - Full-size Image)
In 2009 the AEC(UK) released a BIM Protocol introducing a Model Development Methodology incorporating the Level of Detail/Grade within a classification dedicated purely to geometric aspects (G0-G3). In 2012, the same concept was adopted in Canada by AEC(CAN). However, in 2014, the second version of the BIM Protocol now only refers to the BIMForum LOD Specification released in 2013. In the UK, PAS1192-2, was then published in 2013 and introduced the ‘Level of Definition’, a new classification system with seven levels (1-7) representing both a ‘Level of Model Detail’ (LOD) (for graphic content) and ‘Level of Model Information’ (LOI) (for non-graphic content). This concept was later incorporated, in 2015, into both the NBS BIM Toolkit and the AEC(UK) BIM Technology Protocol, while the CIC BIM Protocol (2013) continues to refer only to Levels of Detail. The UK approach has influenced the last version of the BIMForum LOD Specification (2015) which for the first time includes both Element Geometry and Associated Attribute Information. A new version will be available by July 2016 for public comments.
Another classification deals with the Level of Accuracy (LOA) to represent and document existing conditions. The USIBD guideline (2016) uses different levels (LOA10-LOA50) and incorporates the validation process.
Finally, CityGML has developed five Levels of Detail (LOD0-LOD4) to define geometric details and semantic precision to link BIM with Geographic Information System (GIS) data.
Figure 2: ‘LoX’ relations and evolution (Updated July 22, 2016 - Full-size Image)
The above variations of the same concept have – understandably – caused a large degree of confusion. Below are a few examples:
- The original ‘Level of Detail’ index was intended to measure the reliability of both geometric and non-geometric data, it now focuses more on the geometric attributes;
- The same ‘LOD’ acronym is interchangeable used for both Level of Detail and Level of Development;
- Identical concepts are occasionally referred using different terms (e.g. ‘Level of Information’ and ‘Associate Attribute Information’);
- The Level of Development – while intended to be associated with Model Components – it is sometimes mistakenly associated with whole BIModels; and
- Many BIM documents that these classifications are based on are now out of date.
The below two tables summarize the many different classification systems, within the main BIM documents, intended to specify the level of detail, development or information embedded within Model Components.
Table 1: Comparison of the intended coverage of LoX systems (Updated July 22, 2016 - Full-size Image)
Several classifications (included in Table 2) are already established. However, it is important to underline that – while many share the same name/acronym – they do not necessarily carry the same connotations. For this reason, there is not a perfect coincidence between levels of different classifications and some of them are not well defined as recently discussed by fellow researcher Brian Renehan. In addition, US classifications tend to mainly cover the design and construction phases and focus to a lesser degree on the operation, management and maintenance phase.
Table 2: Comparison of classification systems within different LoX systems (Updated July 22, 2016 - Full-size Image)
To date, the many and increasing LoX concepts have been associated with the incremental progression of information definition within models. However, there are now voices who question whether these types of classification systems accurately represent reality. For example, in order to represent the iterative workflows within the design phase, Drobnik and Riegas (2015) suggest the introduction of Level of Development zero (LOD 0) as well as a negative one (LOD -100).
Also, there has been very little attention given to the link between LoX systems and Model uses as applicable in practice (even if some definitions mention ‘Authorized Uses’). In my opinion, for a LoX system to be applied more intuitively, it needs to be linked (i.e. change according to) targeted Model Uses at each project stage/phase.
An important part of the BIM Processes that is yet to attract ample attention is Verification and Validation. The manual, automatic and semi-automatic compliance checking of information requirements within BIModels is still to be adequately resolved. Current approaches to Model Validation focus on static entities rather than on performing dynamic validation. It is therefore important that future research takes into account - not only the discrete Level of Detail (dLOD) but – the continuous LOD (cLOD), the continuous Level of Information (cLOI), and link both to specific Model Uses as applicable at each project phase/stage.
Another important aspect to address is how to apply LoX systems to existing buildings, as most classifications tend to focus on new construction.
Based on the above, and in collaboration with a number of colleagues, I will be investing additional efforts in trying to resolve some of the issues identified above. I therefore invite all BIM researchers and practitioners to do the same.
The study is part of an ongoing research effort conduced in collaboration with Prof Angelo Luigi Camillo Ciribini (@Ciribini) of University of Brescia (Italy). To review the peer-reviewed paper upon which this post is based, please download ‘The Information Modeling and the Progression of Data-Driven Projects’, as presented at the CIB World Building Congress, Tampere Finland on June 3, 2016.
The topic is in constant flux: new definitions and approaches are being developed and existing definitions are constantly revised. If you discover any inaccuracies or would like to highlight missing information, please add a comment below or contact the author directly.
I would like to thank Bilal Succar for this opportunity to publish through BIM ThinkSpace. I am thankful to Brian Renehan for his comments on earlier works and for exchanging thoughts on different Model Progression Specifications. I would also like to acknowledge the assistance provided by graphic designer Fabiola Pizzuto. Prof. Angelo Ciribini, Amarnath Chegu Badrinath, Prof. Shang-Hsien Hsieh and Zhe Liu. Finally, special thanks to my grandfather for his constant support.
Architectural Engineer | PhD Candidate at Politecnico di Milano, Italy
Marzia Bolpagni is a PhD Candidate at Politecnico di Milano (Italy) where she is investigating ways to manage and control public works through innovative digital approaches. She has worked as BIM researcher at VTT (Finland), ITC-CNR (Italy) and Massachusetts Port Authority (US). She also worked with designers, contractors, public authorities and the Italian Standard Body (UNI) on implementing BIM-based processes. She has presented her work at both national and international fora. After serving as a member of the WBC16 International Scientific Programme Committee for the CIB World Building Congress 2016 and the BIM Roundtable at AIA BSA Foundation, she is currently a member of the VDC & MEP Committee Roundtable at Associated General Contractors of Massachusetts (AGC MA).