In this session, we are going to introduce LOD, which is commonly used but is often misused in the engineering society. So what is LOD? LOD stands for Level of Development? Or Level of Details? In the BIM world, LOD stands for Level of Development. But in other fields, such as the GIS (Geographic Information System) field, LOD stands for Level of Details. Therefore, a lot of time people mix the two in practice. But their definitions are not the same. It is better to clarify it whenever there is a doubt in communication. In AIA’s definition, LOD describes the level of completeness to which a Model Element is developed. A Model Element means an element in the BIM model. It can be just a very simple component or can be a system or assembly of components in the model. Here, we are talking about completeness, that means how complete the model element represents the corresponding real-world object(s). In BIM practice, LOD often refers to the stages that a BIM model (or elements within the model) is expected through the lifecycle of a construction project. Here, the keyword is the “stages”. And there are five levels, labeled from LOD 100 to LOD 500, originally defined in the AIA E202 document. In the AIA Document, LOD, along with Model Element Author (MEA), was needed by the Model Element Table. The purpose of the table is to set up, for each construction stage, the required development completeness for each model element and assign the responsible person for it. Once we have this table set up, both every participant’s responsibility on model element development and the progression of model element development throughout the construction stages become clear. In 2011, the BIMForum of the Associated General Contractors of America (AGC) initiated the development of its LOD Specification and formed a working group for the task. According to the BIMForum, the working group first interpreted the AIA’s basic LOD definitions for each building system and then compiled examples to illustrate the interpretations. The group decided not to address all BIM uses but, instead, the definitions were developed to address model element geometry, with three of the most common uses in mind – quantity take-off, 3D coordination and 3D control and planning. The group felt that in taking this approach the interpretations would be complete enough to support other uses. This slide shows the November 2017 version of the LOD Specification. You can download the specification freely from the AGC BIMForum website. According to the BIMForum, the Level of Development (LOD) Specification is a reference that enables practitioners in the AEC Industry to specify and articulate with a high level of clarity the content and reliability of Building Information Models at various stages in the design and construction process. This one shows how the AGC’s LOD Specification defines LOD. There are six levels of LOD in which LOD 350 does not exist in the original AIA documents and is a new one for representing how building elements interface with various systems and other building elements. Here I will quickly read through the definitions, so you can have some ideas on them. LOD 100: The Model Element may be graphically represented in the Model with a symbol or other generic representation, but does not satisfy the requirements for LOD 200. Information related to the Model Element (i.e. cost per square foot, the tonnage of HVAC, etc.) can be derived from other Model Elements. Elements in LOD 100 are usually developed in Concept Design stage. LOD 200: The Model Element is graphically represented within the Model as a generic system, object, or assembly with approximate quantities, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element. Elements in LOD 200 are usually developed in Schematic Design stage. LOD 300: The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of quantity, size, shape, location, and orientation. Non-graphic information may also be attached to the Model Element. Elements in LOD 300 are usually developed in Detailed Design stage. LOD 350: The Model Element is graphically represented within the Model as a specific system, object, or assembly in terms of quantity, size, shape, orientation, and interfaces with other building systems. Non-graphic information may also be attached to the Model Element. Elements in LOD 350 are usually developed in Construction Document stage. LOD 400: The Model Element is graphically represented within the Model as a specific system, object or assembly in terms of size, shape, location, quantity, and orientation with detailing, fabrication, assembly, and installation information. Non-graphic information may also be attached to the Model Element. Elements in LOD 400 are usually developed in Fabrication & Assembly stage. LOD 500: The Model Element is a field verified representation (i.e., as-built) in terms of size, shape, location, quantity, and orientation. Non-graphic information may also be attached to the Model Elements. Elements in LOD 500 are usually developed in As-Built stage. This slide shows one illustration in the LOD specification to provide graphical examples for different development levels of the steel framing columns. As you can see in the figure, more detailed and precise information is provided as the LOD develops from 100 to 400. The specification also offers some explanation on the difference between Level of Development and Level of Details. Level of Detail is essentially how much detail is included in the model element. It can be seen as a measure of the amount of information provided. Level of Development is the degree to which the element’s geometry and attached information have been thought through – the degree to which project team members may rely on the information when using the model. In essence, Level of Detail can be thought of as an input to the element, meaning how many details in the model you would like to have. While Level of Development is reliable output, meaning how much information in the model we can trust. Before we close this session, let us talk about the misuse of LOD. In practice, LOD is often oversimplified and misused to refer to the development of an entire facility. However, the original intended use of LOD is for indicating the development level of a model element. Furthermore, as mentioned earlier, people may mix the use of level of development and level of details. But they are two different things. Therefore, most people have a misunderstanding that all elements in a BIM model would necessarily become more complete and detailed along the construction lifecycle. However, when we go from the detailed Design Stage to, for example, the fabrication & assembly stage, all elements in the BIM model do not need to become more complete and detailed. Some elements may not be important during the Fabrication & Assembly stage, so they can stay at the lower level of development. This misunderstanding usually results in unneeded efforts and cost in modeling and unnecessary dispute on model delivery. I hope this session gives you a very clear understanding of LOD and its use in BIM applications.
