What is Lod & Everything About it in 3D Modelling

Professionals in the Architecture, Engineering and Construction (AEC) sector can create dependable and intelligible BIM workflows and models throughout various project life cycles by using LOD as a reference framework. LOD 100 through LOD 500 are the six stages of development that are discussed in the article. Each level corresponds to a continual increase in the geometric and informational detail of model pieces. We will also explore the various Levels of Development in 3D modelling.

What is LOD?

The “Level of Development (LOD) Specification” is a reference that enables professionals in the AEC Industry to develop reliable and understandable Building Information Models (BIMs) at different life cycles of their project.

Level of Detail (LOD) popularly refers to the representation of geometric information in a 3D model’s element. LOD specification allows professionals in the industry to clearly articulate how an element’s geometry and associated information have evolved throughout the entire process. It signifies the degree to which different members of the team can rely on information associated with an element.

There are six levels of development, namely, LOD 100, LOD 200, LOD 300, LOD 350, LOD 400, LOD 500. Here, LOD 100 means the model has lower geometric information compared to LOD 200.

Concept and History of LOD

A good overview of the history and evolution of LOD can be found in the article “Many Faces of LOD” by Marzia Bolpagni (MACE). Drawing from that article, the first instance of LOD usage can be traced back to 2004 by a construction analysis software company, Vico Software (now part of Trimble), where they used a LOD-like system to associate digital models with the cost of a project.

The term LOD was later introduced in 2008 by AIA (American Institute of Architects). It introduced five ‘Levels of Development’ (LOD 100 - LOD 500) in the Building Information Modeling Protocol Exhibit, which was further updated in 2013. These documents became the point of reference in several countries – including Australia, Canada, Singapore, China, Taiwan, Germany and France. Other countries developed their variant specification.

The Need for Standardising the “Level of D”

There was a pressing need to standardise the “Level of D” to avoid confusion as this process was very similar across countries and construction projects. For this, concepts such as “level of detail,” “model progression specification” and “level of development ” were established.

One widely-used specification for LOD can be found in the “Level of Development Specification,” which is published and updated yearly by BIMForum and is based on specifications by the American Institute of Architects (AIA).

Here are some of the most important concepts from the BIMForum specification:

• The level of development is stated at an object level, not at the model, since different objects can be at different levels of development across a single model.

• The use of “development” rather than “detail” is used to indicate the degree to which you can rely on the information and not by how much detail there is.

• Five main levels have been defined initially using a numerical label in steps of 100, theoretically allowing for intermediate levels if needed. The labels as such are rather arbitrary but represent the gradual evolution that is typically seen in a project. 

Currently three major LOD matrices are being used in the United States: AIA ,BIMForum, and U.S. Army Corps of Engineers (USACE). Each one has a slightly different approach, but all of them are based on the same concept.

Benefits of LOD

• It helps all the stakeholders involved in a project to work on the same page, so that there are no inconsistencies that hamper a project’s prospects. 
  When all the stakeholders are on the same page, communication and collaboration becomes easier and faster.
• With the help of standardised specifications and detailed information about all the elements, designers can provide guidelines and data for people working downstream to ensure zero lapses in execution and maintenance.
• LOD makes it easier for design managers to explain the requirements from a 3D model at various levels of the design process to the teams in a better manner.
• LOD also makes it easier to define a standard for contractors who must take care of BIM execution.

Why adopt LOD for BIM Model?

In BIM modeling, using Level of Development (LOD) guarantees precision, coherence and clarity throughout project phases. Teams can better grasp the amount of information and detail available at each stage by using it to define the dependability of model pieces. Standardisation increases decision-making, teamwork and mistake reduction, which eventually results in cost savings and effective project execution.

Difference Between Level of Detail and Level of Development

Level of Development vs Level of Detail

There is often a confusion between the two terms - Level of Development and Level of Detail. Let us understand the definitions of both to understand their differences.

1. Level of Development 

The level of development of a BIM model refers to the amount of information which is relevant to the concrete development of the project. It is the degree to which the element’s geometry and attached information has been thought through – the degree to which project team members may rely on the information when using the model.

2. Level of Detail

The level of detail designates the entire amount of information that the BIM element contains. It is essentially how much detail is included in the model element. If all this information is relevant to the setting-up of the construction project, the two concepts overlap.

3. Difference between Level of Detail and Level of Development 

To put simply, “Level of Detail” refers to the graphical representation of an object while “Level of Development” refers both to the graphical representation and to the information (properties) of the object.

Level of Detail is a measure of the amount of information provided to the model element. Because it is only a measure of quantity, the underlying assumption is that all provided information is relevant to the project and so can be relied upon with certainty.

Level of Development is the degree to which the element’s geometry and attached information have been thought through. In essence, Level of Detail can be thought of as input to the element, while Level of Development is reliable output.

Various Levels of Development in BIM

There are six levels of development, namely, LOD 100, LOD 200, LOD 300, LOD 350, LOD 400, LOD 500.

1. LOD 100 - Conceptual Design

At LOD 100, the model would consist of overall building massing and the downstream users are authorised to perform whole building types of analysis (volume, building orientation, cost per square foot, etc.)

2. LOD 200 - Schematic Design

Here, the model would consist of "generalised systems or assemblies with approximate quantities, size, shape, location and orientation." Authorised uses would include "analysis of selected systems by application of generalised performance criteria."

3. LOD 300 - Design Development

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.

4. LOD 350 - Construction Documentation

It includes model detail and elements that represent how building elements interface with various systems and other building elements with graphics and written definitions.

5. LOD 400 - Fabrication and Assembly

Model elements are modelled as specific assemblies, with complete fabrication, assembly, and detailing information in addition to precise quantity, size, shape, location, and orientation. Non-geometric information about the model elements can also be attached. 

6. LOD 500 - As-Built 

Elements are modelled as constructed assemblies for maintenance and operations. In addition to actual and accurate size, shape, location, quantity, and orientation, non-geometric information is attached to modelled elements.

To better understand this, let’s look at the process of detailing a structural kicker. This example has been taken from the book - “BIM and Construction Management” 2nd edition.

• A structural engineer could draw the beams and kickers at LOD 100 in plan view and another LOD 100 detail in elevation.
• The structural engineer could use a hybrid approach where he models the beams at LOD 200 or 300, but uses LOD 100 to annotate the locations of the kickers in plan view and the LO D 100 detail in elevation.
• The structural engineer could model both the beams and the kickers, but place the kickers in the correct location but at a general angle (LOD 200).
• The structural engineer could model both the beams and kickers at LOD 300 (or better) and use the parametric capabilities of BIM to automatically generate an elevation view equivalent.

Conclusion 

In conclusion, professionals working in the fields of architecture, engineering and construction must comprehend and use the Level of Development framework. Project teams may guarantee consistency, enhance stakeholder communication and enable effective project execution and maintenance by following defined LOD standards. In addition to making the evolution of model elements more understandable, the organised approach of LOD improves the general dependability and efficiency of BIM installations.

I hope this blog gave you the insight you needed to accelerate your career in the Architecture, Engineering and Construction (AEC) Industry by helping you understand the key concepts of BIM.

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