Levels of detail for information model elements (LODs) are one of the most important components of the BIM “language”, and the concept of LOD is one of the most discussed topics in the global BIM community today. To be convinced of this, just look at the variety of terms associated with levels of detail: “Level of Detail”, “Level of Development”, “Level of model Definition”, ”Depth of Detail”, etc.
We will consider the history of the concept of LOD and its interpretation according to some versions and specifications of various organizations, but first, we will determine the importance of this concept and its place in the context of the information modeling process.
BIM and the concept of LOD
In general, the level of detail (LOD) determines the completeness of an information model element. It determines how much graphic and non-graphic (attributive) information is required for a specific element of the information model at a certain stage of its development.
Obviously, the levels of detail should meet the specific needs of all project stakeholders at each stage. In this regard, the level of detail does not have to be a measure of the informational and graphical “saturation” of the element. So, for example, to prepare an estimate and to draw up a custom specification for an element of engineering equipment (for example, a pump), you do not need to know exactly how it looks, its exact dimensions, and technological characteristics.
But data on its label, manufacturer, catalog cost, weight, etc. are absolutely necessary. And vice versa, an engineer needs detailed geometry, dimensions, and technological parameters to implement 3D coordination and control of model elements (to identify “hard” and “soft” collisions).
Thus, the first place is given to the task of obtaining the minimum necessary, but sufficient information by each participant in the information modeling process to solve specific problems at a certain project stage.
As we can see, the concept of LOD is extremely important for planning the information modeling process. It answers the questions:
- what? (which element of the model)
- what information should this element contain?
- when? (at what point in time)
- from whom should this information be transferred?
- to whom should this information be transferred?
The use of LOD is also extremely important at the stage of the preparation of technical specifications for design and modeling.
When preparing a technical assignment for a design using BIM technologies, the technical customer formulates the goals and objectives of using information models. Depending on this, the required levels of detail for various elements of the model are pre-set.
For example, if it is necessary to use a model for assessing economic indicators or searching for interdisciplinary collisions, then it would be reasonable not to work out in detail the nodes of metal structures.
Another aspect that justifies the concept of using LOD for information modeling is related to the display of representations in traditional (2D) design and BIM. In drawings, as a rule, there are many dimension lines, tables, notes, annotations. Knowing them you can operate with the amount of information about the object represented in the drawings.
In an information model, elements of the same appearance can often contain very different amounts of information. Levels of detail, in this case, allow you to determine the differences between model elements without checking and comparing the properties (attributes) of each element separately.
In order to understand the concept of LOD, it is also important to consider that model elements progress at different speeds. This is primarily due to the fact that all sections of the project cannot begin to be developed at the same time. It follows that the concept of LOD can only be applied to individual elements of the model, but not to the model as a whole, and, accordingly, LOD cannot strictly correspond to a certain stage of the project.
In 2004, the “Level of Detail” concept was introduced by Vico Software, a company specializing in the production of software for managing construction projects and performing cost estimates. Vico Software at that time saw the main purpose of LOD in determining the cost of construction at various stages of the project. (In 2012, Vico Software was acquired by Trimble)
The initial interpretation of the term “Level of Detail” defined the level of detail as the degree of graphical and informational saturation of the model elements, but did not touch upon the issue of the minimum sufficiency of this information for use by other project participants.
The main goal was to determine the cost of a construction project at various stages: from estimating the approximate cost at the conceptual stage to determining the exact cost at release stages of working documentation and the production of construction and installation works.
In 2008, the American Institute of Architecture (AIA) developed the LOD concept in the form of AIA E202-2008, Building Information Modeling Protocol Exhibit (Typical Application Form to a BIM Project Contract). Today, there are improved versions of this protocol: AIA E203–2013 Building Information Modeling and Digital Data Exhibit and AIA Contract Document G202-2013 Building Information Modeling Protocol Form.
In these documents, the level of detail has been defined as the “Level of Development” of the model elements. This renaming of the term “Level of Detail” was reasonable, but nevertheless introduced some confusion in the general BIM terminology because the abbreviation remains the same – LOD.
According to the latest version of the protocol (E203–2013), LOD determines the minimum amount of geometric, spatial, quantitative, and other data of a model element, sufficient for basic implementations of using models corresponding to this type of detail.
To organize the planning of a BIM project, to implement 3D coordination and transfer the necessary information to solve the main design tasks, five basic levels of detail for the elements of information models were determined: LOD100, LOD200, LOD300, LOD400, and LOD500. You can learn more about levels of detail in this document: https://www.gsa.gov/level-of-detail
Levels in the LOD specification:
LOD 100 – low level of elaboration with a conditional representation of the component. A conditional object with the minimum detail required for identification.
LOD 200 is a conventional object with the minimum information processing required for making economic decisions.
LOD 300 – Design model with specific and precise values for shape, position, and key attributes.
LOD 400 – a high level of elaboration with the most detailed graphical presentation and filling with information in properties. In fact, it is LOD 300 + detailing of nodal connections, plus manufacturing, cost and installation data.
LOD 500 = LOD 400 + as-built documentation and performance specifications.