An Updated look at LoD

As BIM authors become more adept it quickly becomes apparent that a more hybrid understanding of 3D graphics is required.  This new level of modeling takes the technical drafter down the road closer toward a visualization or animator role.  Therefore a more specific description of Level of Detail/Development is required.  (Each RPF or BIM Implementation needs to have a section defining LoD as it’s specifics mean different things to different people.)

It it important to note that Level of Detail and Level of Development are different things… Level of Development outlines what a model is authorized to be used for while Level of Detail describes the model’s graphical properties and goes together with Level of Appearance Quality (LoAQ).

Level of Detail in General

LoD1: Buildings are represented by their footprint or the roof outline with a constant height value.  Inclusion of some density data or distances are possible.

LoD2: Buildings are represented by massing models.

LoD3: Buildings are represented by geometrically simplified exterior shell.  Analysis of the materials is possible leading to an estimated ‘R’ value of the wall assembly & energy conservation performance.

LoD4: Buildings are represented by geometrically exact exterior shells.

LoD5: Building interiors are included.

Geometric Level of Detail (GLoD)

GLoD1: Buildings are represented as 2D surfaces inserted into 3D space.

GLoD2: Buildings are represented as simple 3D geometry.

GLoD3: Buildings elements that are 15cm and larger are included.

GLoD4: Buildings elements that are 5cm and larger are included.

GLoD5: Buildings elements that are 1cm and larger are included.

Level of Appearance Quality (LoAQ)

LoAQ0: No minimum appearance quality is specified.

LoAQ2: Buildings are represented as “shaded with edges” and indicates true colour.  Includes shadows

LoAQ3: Building on the requirements of LoAQ2 but is expanded to include material mapping.

LoAQ4: Building on the requirements of LoAQ3 but is expanded to include full texture mapping (bump maps, transparency, luminance, reflectance…) to produce a photo real environment.

Level of Development

The AIA has produced document E202*, which addresses the issue of integrating BIM data into the contractual environment.  The key part of which is the definition of two fundamental concepts:

• Level of Development (LOD) and
• Model Element Author (MEA)

There are 5 basic Levels of Development which do not reflect specific modeling guidelines for any particular software, but rather a generic definition of model detail and, more importantly, authorized uses of the model component for the respective LOD:

*  The AIA Document E202 is a copyright of The American Institute of Architects and is protected by U.S. Copyright Law and International Treaties.

Authorized Use	Description
You should be able to Visualize it	LOD 100 conceptual design -overall conceptual massing -downstream users are authorized to perform overall types of analysis (volume, orientation, cost per square foot, etc.)
You should be able to Specify it	LOD 200 schematic design or design development -generalized systems or assemblies with approximate quantities, size, shape, location and orientation -authorized uses would include analysis of selected systems by application of generalized performance criteria.
You should be able to Buy it	LOD 300 construction documents -model elements are suitable for the generation of traditional CD’s & shop drawings -analysis and simulation is authorized for detailed elements and systems
You should be able to Build or Install it	LOD 400 fabrication and assembly The MEA for this LOD is most likely to be the trade contractor or fabricator as it is usually outside the scope of the designer’s services or would constitute severe risk exposure if such parties are not adequately insured
You should be able to Operate or Maintain it	LOD 500 as built The final level of development represents the element as it has been constructed. The model is suitable for maintenance and operations.

Note that the above descriptions are merely excerpts from the original AIA E202 document. Refer to the free sample available from AIA’s Contract Documents website for complete details.

Model Element Authors (MEA’s) are the parties responsible for developing the model content as specified in the Model Element Table. The Levels of Development are paired with an assigned MEA for each major building assembly as shown in a filled-out sample below:

According to the AIA E202 document, LOD is defined as “level of development”.  It does NOT mean “level of detail”:

• Level of detail is the amount of information and geometry provided by the content author. There can always be a higher level of detail in a project model than what is realistic to be used by others in a downstream workflow.
• Level of development is the maximum amount of information and geometry that is authorized for use by others.

It is important to separate the milestone deliverables from your thinking about LOD’s. Don’t think that schematic design = LOD100; design development = LOD200; and so on.  At any given project milestone, you will likely have a combination of LOD’s. For example, at the end of construction documents, the interior walls and doors might be at LOD300, furniture is at LOD200, and information about electrical fixtures is only supplied as an allowance per square foot; thus LOD100.